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Basic Hazard Awareness “This material was produced under the grant SH-20839-SHO from the Occupational Safety and Health Administration, U.S. Department of Labor. It does not necessarily reflect the views or policies of the U.S. Department of Labor, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.” Objectives By the end of this workshop, you will:   Identify how workplace injuries or illnesses can affect your everyday life. Identify common symptoms, aches/pains, illnesses and injuries that are associated with your work. Identify and recognize the exposures and hazards linked to work-related illnesses and injuries. Develop solutions and strategies to address these identified hazards. CHEMICAL & DUST HAZARDS (cleaning products, pesticides, asbestos, etc.) BIOLOGICAL HAZARDS (mold, insects/pests, communicable diseases, etc.) ERGONOMIC HAZARDS (repetition, lifting, awkward postures, etc.) WORK ORGANIZATION HAZARDS Things that cause STRESS! SAFETY HAZARDS (slips, trips and falls, faulty equipment, etc.) PHYSICAL HAZARDS (noise, temperature extremes, radiation, etc.) 3 Hierarchy of Controls Requires a physical change to the workplace Requires worker to wear something Elimination/Substitution Requires worker or employer to do something Most Effective Least Effective These are referred to as the hierarchy of controls, how you prevent or control a hazard: Elimination/Substitution: The main goal for any fix to a hazard or exposure is to eliminate it altogether or substitute a product or method of doing the work to a less hazardous alternative. (e.g. green cleaning products) 4 CONTROLS: Engineering CONTROL AT THE SOURCE! Limits the hazard but doesn’t entirely remove it. Local Exhaust Other Examples: Mechanical Guards Wet Methods for Dust Enclosures/Isolation Dilution Ventilation Proper equipment Re-designed Tools Image: by Kare_Products Image: by JohnRH4's photostream Image: by purpleslog’s photostream 5 The basic concept behind engineering controls is that, to the extent feasible, the work environment and the job itself should be designed to eliminate hazards or reduce exposure to hazards. While this approach is called engineering controls, it does not necessarily mean that an engineer is required to design the control. Engineering controls are the "first line of defense" against injury/illness, because they have the potential to completely eliminate a hazard, and do not rely on human behavior to be effective. For instance, rather than require employees to wear respiratory protection which must be monitored, inspected, trained, managed, it's much more effective to install a ventilation system that does not require any of those management activities or, better yet, find an alternative substitute that is less hazardous. Images from: Creative Commons: You are free: to Share — to copy, distribute and transmit the work to Remix — to adapt the work Under the following conditions: Attribution — You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work). Image: by Kare_Products Image: by JohnRH4's photostream Image: by purpleslog's photostream CONTROLS: Administrative Aimed at Reducing Employee Exposure to Hazards but Not Removing Them! Changes in work procedures such as: Written safety policies/rules Schedule changes, such as: Lengthened or Additional Rest Breaks Job Rotation Adjusting the Work Pace Training with the goal of reducing the duration, frequency and severity of exposure to hazards 6 Administrative controls (or work practice controls) are changes in work procedures such as written safety policies, rules, supervision, schedules, and training with the goal of reducing the duration, frequency, and severity of exposure to hazardous chemicals or situations. As with work practice controls, administrative controls normally are used in conjunction with other controls that more directly prevent or control exposure to hazard. Image: Powerpoint Clipart CONTROLS: PPE Personal Protective Equipment Control of LAST RESORT! Special Clothing Eye Protection Hearing Protection Respiratory Protection 7 CONTROL IS AT THE WORKER! 7 Personal protective equipment (PPE): A method that prevents a worker from being exposed to the hazard by something the worker wears (e.g., gloves, hardhat, of safety glasses). PPE is considered the method of last resort because PPE does nothing to reduce or eliminate the hazard. If the PPE fails, immediate exposure is the result. Examples of PPE include:   a.   Special clothing: like gloves, aprons, boots, coveralls, etc.   b.   Eye protection: like safety glasses or face shields   c.   Hearing protection Respiratory protection: for emergency or short-term protection. Images: all from OSHA website Hierarchy of Controls Requires a physical change to the workplace Requires worker to wear something Elimination/Substitution Requires worker or employer to do something Most Effective Least Effective 8 OSHA STATE PLAN STATES This map shows that our public employee members in 27 states enjoy the same OSHA rights as all workers in the private sector. They have a legal right to a safe and healthy workplace.   All public employers in the 27 OSHA states are required to follow OSHA standards. When they are not in compliance, workers and their unions have the right to file a complaint and receive an inspection if they feel that their working conditions are unsafe.   But, the map also shows that there are millions of public workers in the rest of the states that have no OSHA protection. Unfortunately, any type of protection for public employees in non-OSHA state plan states are spotty at best.   Even with OSHA coverage … many of the hazards we are exposed to everyday don’t have standards that address them. Image: Pamela Wolfe, AFT 9 OSHA Asbestos Standard Applies in all 50 states for school employees Provides protection for custodians and maintenance workers who must remove or handle asbestos as part of their duties. OSHA also protects any school employee in any state who is harassed or discriminated against for complaining about asbestos exposure. Image: by Beige Alert's photostream Image: by Beige Alert's photostream 10 Valuable resource for information on all types of hazard exposures Can conduct Health Hazard Evaluations (HHE) if requested by union or members The National Institute for Occupational Safety and Health (NIOSH), the research arm of OSHA is another valuable resource for information on hazard exposures. They can also come into workplaces and do Health Hazard Evaluation (HHE) if requested by the union or members in response to a hazard exposure. Images: NIOSH 11 OSHA 300 Log of Injuries and Illnesses Employer must post all work-related injuries and illnesses that result in a day or more away from work. You have a right to request copies and/or see log. Employer must post a summary of these logs each year from February 1 – April 30. Required in the 27 state plan states that cover public employees. This is a model for what should be required for all workplaces. Image: OSHA PDF 12
1 Course Learning Outcomes for Unit VII Upon completion of this unit, students should be able to: 7. Evaluate types of hazard controls. 7.1 Discuss the use of elimination/substitution for controlling occupational hazards. 7.2 Discuss the use of engineering controls for occupational hazards. 7.3 Discuss the use of administrative controls for occupational hazards. Reading Assignment To access the following resources, click on the links below: Occupational Safety and Health Administration. (n.d.). Chemical hazards and toxic substances: Controlling exposures. Retrieved from https://www.osha.gov/SLTC/hazardoustoxicsubstances/control.html Occupational Safety and Health Administration. (n.d.). Basic hazard awareness [PowerPoint slides]. Retrieved from https://www.osha.gov/sites/default/files/2018-11/fy10_sh-20839- 10_basic_hazard_awareness.pptx Occupational Safety and Health Administration. (n.d.). OSHA technical manual—Section III: Chapter 3 Ventilation Investigation. Retrieved from https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html Unit Lesson The last of the four tenets of industrial hygiene that we will study is control. The first three tenets— anticipation, recognition, and evaluation—identify hazards and the level of risk for each hazard. Controls then are used to reduce the risk associated with the hazards to an acceptable level. Risk assessment is a valuable tool in prioritizing expenditures for control methods. Controls will be implemented first for hazards with the highest level of risk. The Occupational Safety and Health Administration (OSHA) established a hierarchy of controls for occupational hazards. It illustrates OSHA’s preferred approach for hazard control. As summarized in the diagram below, the Hierarchy of Controls includes elimination/substitution, engineering controls, administrative controls (including work practices), and personal protective equipment (PPE). In looking at protection from occupational hazards, the most effective method is to prevent an exposure from occurring in the first place; however, this is not always possible in occupational settings. Therefore, the next Course/Unit Learning Outcomes Learning Activity 7.1 Unit VII Lesson Article: “Basic hazard awareness [PowerPoint slides]” Unit VII Assessment 7.2 Unit VII Lesson Unit VII Assessment 7.3 Unit VII Lesson Article: “Basic hazard awareness [PowerPoint slides]” Unit VII Assessment UNIT VII STUDY GUIDE Hazard Controls https://www.osha.gov/SLTC/hazardoustoxicsubstances/control.html https://www.osha.gov/sites/default/files/2018-11/fy10_sh-20839-10_basic_hazard_awareness.pptx https://www.osha.gov/sites/default/files/2018-11/fy10_sh-20839-10_basic_hazard_awareness.pptx https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html 2 UNIT x STUDY GUIDE Title priority is to prevent harm to exposed individuals. Finally, if harm occurs, the priority is to limit the harm as much as possible. OSHA’s Hierarchy of Controls is designed to meet these priorities. The first control method in OSHA’s Hierarchy of Controls is elimination/substitution. This control method is always the most effective and preferred method because it prevents the exposure from occurring in the first place. If you remove a specific hazard completely from a workplace, no one can be exposed to that hazard. For example, if a facility is using a solution containing styrene to clean parts, there is a health risk from exposure to the styrene, both through inhalation and dermal exposure. If the facility determined that the cleaning could be performed using only water, the exposure to styrene would be completely eliminated for that particular task. This approach sounds simple but is much more complicated in practice. If, for example, a solvent solution is needed to clean a part, water would not be effective. Therefore, this approach would change to evaluating other chemicals effective in performing the same task and choosing one that would produce the lowest risk to employees. In the example above, some employers have changed from a solvent like styrene to a solvent like acetone. Acetone has a lower toxicity than styrene, so health risks will be reduced. Nevertheless, reducing a health risk may increase other risks. Acetone is more flammable than styrene, so substituting acetone may reduce health risks but increase the risk of a fire. Of course, there may be situations where specifications require the use of a specific chemical and thus the use of elimination/substitution is untenable. If the hazard cannot be eliminated from the workplace, residual risks will remain. Additional controls will be designed to reduce the risk associated with the hazard. In evaluating the use of control methods, one must always ask what level of residual risk will be acceptable. Once the acceptable level of residual risk has been determined, the rest of the controls in OSHA’s Hierarchy of Controls can be applied, in order of preference, until the residual risk has been lowered to the acceptable level. The acceptable level of residual risk is a debated topic. Certainly, for exposures to chemical and physical hazards that industrial hygienists evaluate, the established OSHA permissible exposure limits (PELs) represent what should be accepted as residual risks. One would think exposures below the OSHA PELs are either safe or at least below a level where the residual risk would be significant, but this is not always true. OSHA should consider technological and economic feasibility in addition to risk assessments when they establish PELs. In some instances, exposures at the established PELs continue to carry significant risks of morbidity and mortality, even by OSHA’s definition of significant risk. OSHA has historically used a residual risk of 1 in 1,000 as being significant; this is based on a Supreme Court decision in 1980. Any residual risk exceeding that level is considered significant by OSHA. In many cases, OSHA has estimated the residual risk to exceed this level for lifetime exposures at new PELs. For example, OSHA recently released new PELs for crystalline silica. Under the old PELs, OSHA estimated the risk of death from silicosis to be 11:1,000 in general industry and 17:1,000 in the construction industry. For exposures at the newly published PEL, OSHA estimates the risk of death from silicosis at 7:1,000 for both general industry and construction. At the new action level, OSHA estimates the risk of death from silicosis at 4:1,000 for both general industry and construction. Significant residual risk of death is also present for exposures at the PEL for both asbestos and hexavalent chromium. For this reason, many employers may choose to use more stringent control methods than those required by OSHA. Basic hazard awareness diagram (Occupational Safety and Health Administration [OSHA], n.d.) 3 UNIT x STUDY GUIDE Title The next preferred control method in the Hierarchy of Controls is engineering controls. Because it may be difficult to eliminate a hazard or substitute a less hazardous chemical for a process, engineering controls are the most commonly used control method for occupational settings. Many different engineering controls are used. In some cases, the process can be isolated or enclosed to separate the worker from the hazard. An example would be to place a machining process inside an enclosure with a lid that opens and closes and to provide automatic sprayers that apply metalworking fluids. The employee opens the door to the machine, removes the part, and places another part inside the machine. The metalworking fluid is not applied, and the machining process will not start until the door is closed. Industrial hygiene evaluations have shown that exposures to metalworking fluids still occur because the hazard is still present, but the exposures are lower than they would be with an open process. Engineering controls can also address noise hazards, for example, in using enclosure and isolation methods to reduce noise hazard risk. The enclosures, however, will require the use of specific materials. As discussed in Unit VI, noise propagates through air as a wave, and noise hazards from a single source can be present at different frequencies. Noise-deadening materials are typically effective at reducing dB levels based on frequencies. The use of the octave band filter with a sound level meter, as discussed in Unit VI, can provide the information necessary to choose materials for a noise enclosure that will be effective in reducing noise levels from a specific source. Another engineering control involves wet methods. These methods are specified in some regulations such as OSHA’s asbestos in construction regulation. Because significant residual risk remains for exposures at the PEL, OSHA has specified wet methods (and respiratory protection) for some tasks involving asbestos removal, even if exposures have been shown to be below the PEL. Wet methods are designed to reduce, but not completely eliminate, the concentration of an aerosol hazard in the air. Ventilation is one of the most common engineering controls. Two types of ventilation can reduce exposure to hazards: general dilution ventilation and local exhaust ventilation (LEV) systems. The nature of a hazard and the risk associated with that hazard, will help determine the ventilation system with the best protection. General dilution ventilation systems merely blow fresh air into a work area to dilute the concentration of an air hazard. A typical dilution ventilation system in a workplace consists of a fan or fans in the ceiling or through an exterior wall. The fans blow either fresh air into the work area or move air from inside the work area to outside the building. Fresh air in the latter case will come through other openings in the building. The use of portable fans placed in the work area can also be considered dilution ventilation, though they are not typically as effective. An example using the metalworking operation would be to place large fans in the ceiling above the machines and blow fresh air through the area, reducing the employees’ exposure to metalworking fluids. In many cases, the use of dilution ventilation is adequate to reduce exposures to an acceptable risk level. LEV systems collect the air at the source and move it somewhere else through duct systems. Where the contaminated air is moved depends on how it will be treated. Sometimes the air is simply discharged to the outside air. Other contaminants require some type of treatment, such as filtration or disintegration. Whether the air can be released directly to the outside air or needs some type of collection or treatment will depend on the specific compound. Some chemicals are too toxic to release into the outside air directly, and some states have regulations controlling the release of specific chemicals from a facility. An example using the metalworking fluid operation is to place an LEV above or near the machine to collect and filter out aerosols associated with the fluids. This type of LEV is commonly called a smog hog by industry. Another example of using an LEV would be laboratory fume hoods commonly found in laboratory settings. Although called fume hoods, they typically are used for gases and vapors, not fumes. The next level of controls on OSHA’s Hierarchy of Controls is administrative and work practice controls. These do not provide the level of controls that engineering controls can, but may further reduce residual risk if the engineering controls cannot reduce the residual risk to an acceptable level. Administrative controls can reduce risk by limiting the amount of time an employee spends in a certain area. Let’s say a certain task requires work near a machine that produces constant noise levels exceeding 100 dBA. The first approach would be to apply some type of sound barrier to reduce the exposure. If this was not possible, employees could be rotated into and out of the area to limit their total exposure to a point below the OSHA PEL and action level. Work practice controls could also be used to evaluate the standard operating procedures used by employees, and then work practices could be changed to reduce exposures. For example, if a job has been performed 4 UNIT x STUDY GUIDE Title during the first work shift, and there is an unacceptable risk of heat illness in the summer, the work could be moved to the third shift during periods of lower temperatures to reduce the risk. Reference Occupational Safety and Health Administration. (n.d.). Basic hazard awareness [PowerPoint slides]. Retrieved from https://www.osha.gov/dte/grant_materials/fy10/sh-20839- 10/basic_hazard_awareness.pptx Suggested Reading To access the following resources, click on the links below: Implementing engineering controls for some occupational noise sources may prove difficult. The following article evaluates the use of a fairly simple engineering control method for reducing noise during tire manufacturing operations. Cockrell, W. T., Jr., Balanay, J. A. G., & Dawkins, W. (2015). Engineering case reports: Engineering control of noise from 4-roll calender operations in tire manufacturing. Journal of Occupational and Environmental Hygiene, 12(9), D193–D200. Retrieved from https://libraryresources.waldorf.edu/login?auth=CAS&url=http://search.ebscohost.com.libraryresource s.waldorf.edu/login.aspx?direct=true&db=aph&AN=109017162&site=ehost-live&scope=site The construction industry sometimes presents unique problems for ventilation systems. There are some commercially available LEV systems for tools used in the construction industry. The following article evaluates a commercially available LEV used for cutting roof tiles containing crystalline silica. Garcia, A., Jones, E., Echt, A. S., & Hall, R. M. (2014). Case study: An evaluation of an aftermarket local exhaust ventilation device for suppressing respirable dust and respirable crystalline silica dust from powered saws. Journal of Occupational and Environmental Hygiene, 11(11), D200–D207. Retrieved from https://libraryresources.waldorf.edu/login?url=https://doi.org/10.1080/15459624.2014.955182 Diacetyl is a chemical that has received much press coverage because of serious health effects in workers at microwave popcorn factories. Sometimes when new manufacturing processes and health hazards are discovered, new engineering controls have to be invented. The article below discusses engineering controls developed by researchers at NIOSH for diacetyl operations at a microwave popcorn manufacturing facility. Hirst, D. V. L., Dunn, K. H., Shulman, S. A., Hammond, D. R., & Sestito, N. (2014). Evaluation of engineering controls for the mixing of flavorings containing diacetyl and other volatile ingredients. Journal of Occupational and Environmental Hygiene, 11(10), 680–687. Retrieved from https://libraryresources.waldorf.edu/login?auth=CAS&url=http://search.ebscohost.com.libraryresource s.waldorf.edu/login.aspx?direct=true&db=bxh&AN=BACD201400496422&site=ehost-live&scope=site OSHA sometimes publishes requirements for ventilation in regulations. The following document contains links to several regulations discussing ventilation requirements. Occupational Safety and Health Administration. (n.d.). Ventilation: Possible solutions. Retrieved from https://www.osha.gov/SLTC/ventilation/solutions.html The following OSHA document contains a summary of control methods for noise hazards. It also contains links to other web sites with information about noise controls and some case studies. Occupational Safety and Health Administration. (n.d.). Occupational noise exposure: Exposure and controls. Retrieved from https://www.osha.gov/SLTC/noisehearingconservation/evaluation.html https://online.waldorf.edu/CSU_Content/Waldorf_Content/ZULU/EmergencyServices/OSH/OSH4301/W16Gc/UnitVIIReading1.pdf https://online.waldorf.edu/CSU_Content/Waldorf_Content/ZULU/EmergencyServices/OSH/OSH4301/W16Gc/UnitVIIReading1.pdf https://libraryresources.waldorf.edu/login?url=https://doi.org/10.1080/15459624.2014.955182 https://online.waldorf.edu/CSU_Content/Waldorf_Content/ZULU/EmergencyServices/OSH/OSH4301/W16Gc/UnitVIIReading2.pdf https://online.waldorf.edu/CSU_Content/Waldorf_Content/ZULU/EmergencyServices/OSH/OSH4301/W16Gc/UnitVIIReading2.pdf https://www.osha.gov/SLTC/ventilation/solutions.html https://www.osha.gov/SLTC/noisehearingconservation/evaluation.html 5 UNIT x STUDY GUIDE Title Learning Activities (Nongraded) Non-graded Learning Activities are provided to aid students in their course of study. You do not have to submit them. If you have questions, contact your instructor for further guidance and information. There are several free sound level meter applications (apps) for smartphones available on the Internet. Download one of the apps, and use it to measure the sound levels, in dBA, of some noise sources around your home and workplace. Do any of the readings surprise you? Which sources were high enough that you would be concerned about hearing loss?
1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 1 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html UNITED STATES DEPARTMENT OF LABOR ! " # $ % & Section III: Chapter 3 Ventilation Investigation Table of Contents: I. Introduction II. Health Effects III. Standards and Codes IV. Investigation Guidelines V. Prevention and Control VI. Bibliography List of Appendices: Appendix III:3-1. Ventilation Primer Appendix III:3-2. Glossary Appendix III:3-3. OSHA and Consensus Standards Appendix III:3-4. Troubleshooting an Exhaust System--Some Helpful Hints For problems with accessibility in using figures and illustrations in this document, please contact the Office of Science and Technology Assessment at (202) 693-2095. I. Introduction Industrial ventilation generally involves the use of supply and exhaust ventilation to control emissions, exposures, and chemical hazards in the workplace. Traditionally, nonindustrial ventilation systems commonly known as heating, ventilating, and air-conditioning (HVAC) systems were built to control temperature, humidity, and odors. A. Ventilation may be deficient in: confined spaces; facilities failing to provide adequate maintenance of ventilation equipment; facilities operated to maximize energy conservation; windowless areas; and areas with high occupant densities. Any ventilation deficiency must be verified by measurement. B. There are five basic types of ventilation systems: 1. dilution and removal by general exhaust; 2. local exhaust (see Figure III:3-1); Occupational Safety and Health Administration CONTACT US FAQ A TO Z INDEX ENGLISH ESPAÑOL OSHA STANDARDS TOPICS HELP AND RESOURCES https://www.dol.gov/ https://www.facebook.com/departmentoflabor https://twitter.com/OSHA_DOL https://www.instagram.com/USDOL/ https://www.osha.gov/rss/ https://www.osha.gov/quicktakes%23subscribe https://www.youtube.com/user/USDepartmentofLabor/ https://www.osha.gov/ https://www.osha.gov/contactus https://www.osha.gov/faq https://www.osha.gov/a-z javascript:doGTranslate('en%7Cen') javascript:doGTranslate('en%7Ces') https://www.osha.gov/aboutosha https://www.osha.gov/laws-regs https://www.osha.gov/SLTC/ https://www.osha.gov/news 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 2 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html Figure III:3-1. Components of a Local Exhaust System 3. makeup air (or replacement); 4. HVAC (primarily for comfort); and 5. recirculation systems. C. Ventilation systems generally involve a combination of these types of systems. For example, a large local exhaust system may also serve as a dilution system, and the HVAC system may serve as a makeup air system (see Appendix III:3-1 for a primer and Appendix III:3-2 for an explanation of these terms). II. Health Effects Inadequate or improper ventilation is the cause of about half of all indoor air quality (IAQ) problems in nonindustrial workplaces (see Section III, Chapter 2, Indoor Air Quality). This section of the manual addresses ventilation in commercial buildings and industrial facilities. A. Indoor Air Contaminants Indoor Air Contaminants include but are not limited to particulates, pollen, microbial agents, and organic toxins. These can be transported by the ventilation system or originate in the following parts of the ventilation system: wet filters; wet insulation; wet undercoil pans; cooling towers; and evaporative humidifiers. People exposed to these agents may develop signs and symptoms related to "humidifier fever," "humidifier lung," or "air conditioner lung." In some cases, indoor air quality contaminants cause clinically identifiable conditions such as occupational asthma, reversible airway disease, and hypersensitivity pneumonitis. B. Volatile Organic and Reactive Chemicals Volatile Organic and Reactive Chemicals (for example, formaldehyde) often contribute to indoor air contamination. The facility's ventilation system may transport reactive chemicals from a source area to other parts of the building. Tobacco smoke contains a number of organic and reactive chemicals and is often carried this way. In some instances the contaminant source may be the outside air. Outside air for ventilation or makeup air for exhaust systems may bring contaminants into the workplace (e.g., vehicle exhaust, fugitive emissions from a neighboring smelter). See Section III, Chapter 2, Indoor Air Quality, for a discussion of common indoor-air contaminants and their biological effects. III. Standards and Codes A. Consensus Standards Appendix III:3-3 is a compilation of OSHA and industry consensus standards. Foremost are those recommended by the Air Movement and Control Association (AMCA), the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), the American National Standards Institute (ANSI), the Sheet Metal and Air Conditioning Contractors National Association (SMACNA), the National Fire Protection Association (NFPA), and the American Conference of Governmental Industrial Hygienists (ACGIH). AMCA is a trade association that has developed standards and testing procedures for fans. ASHRAE is a society of heating and air conditioning engineers that has produced, through consensus, a number of standards related to indoor air quality, filter performance and testing, and HVAC systems. ANSI has produced several important standards on ventilation, including ventilation for paintspray booths, grinding exhaust hoods, and open- surface tank exhausts. Four ANSI standards were adopted by OSHA in 1971 and are codified in 29 CFR 1910.94; these standards continue to be important as guides to design. ANSI has recently published a new standard for laboratory ventilation (ANSI Z9.5). SMACNA is an association representing sheet metal contractors and suppliers. It sets standards for ducts and duct installation. NFPA has produced a number of recommendations (which become requirements when adopted by local fire agencies), e.g., NFPA 45 lists a number of ventilation requirements for laboratory fume hood use. The ACGIH has published widely used guidelines for industrial ventilation. B. OSHA Regulations https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9734 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 3 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html Table III:3-1. Common Ventilation Conditions and Causes Condition Possible cause(s) Worker complaints, improper use of system, nonuse of system, alteration of system by employees. The hood interferes with work The hood provides poor control of contaminants. Excessive employee exposures although flow volumes and capture velocities are at design levels. Employee work practices need improvement. The ventilation system interferes with work or worker productivity and leads workers to bypass the system. Employee training is not adequate. Design of system is poor. Constant plugging of duct. Plugged ducts occur when transport velocity is inadequate or when vapor condenses in the duct, wets particles, and causes a build-up of materials. These problems are caused by poor design, open access doors close to the fan, fan problems, or other problems. Reduced capture velocities or excessive fugitive emissions. The cause of these conditions is usually reduced flow rate, unless the process itself has changed. Reduced flow rate occurs in the following situations: plugged or dented ducts slipping fan belts open access doors holes in ducts, elbows closed blast gate to branch, or opened blast gates to other branches, or corroded and stuck blast gates fan turning in reverse direction (This can occur when lead wires are reversed and cause the motor and fan to turn backwards. Centrifugal fans turning backwards may deliver up to only 50% of rated capacity.) worn out fan blades additional branches or hoods added to system since initial installation, or clogged air cleaner. Table III:3-2. Problem Characterization Emission source Where are all emission sources or potential emission sources located? Which emission sources actually contribute to exposure? What is the relative contribution of each source to exposure? Characterization of each contributor: chemical composition Ventilation criteria or standards are included in OSHA regulatory codes for job- or task-specific worker protection (see Appendix III:3-3). In addition, many OSHA health standards include ventilation requirements. The four standards in 29 CFR 1910.94 deal with local exhaust systems, and OSHA's construction standards (29 CFR 1926) contain ventilation standards for welding. OSHA's compliance policy regarding violation of ventilation standards is set forth in the Field Inspection Reference Manual. IV. Investigation Guidelines A. Investigation Phases Workplace investigations of ventilation systems may be initiated by worker complaints of possible overexposures to air contaminants, possible risk of fire or explosion from flammable gas or vapor levels at or near the lower explosive limit (LEL), or indoor air quality complaints. The second phase of the investigation involves an examination of the ventilation system's physical and operating characteristics. B. Faulty Ventilation Conditions and Causes Common faulty ventilation conditions and their probable causes are listed in Table III:3-1. Specific points to consider during any investigation of a ventilation system include emission source, air behavior, and employee involvement. Points that should be included in a review of operational efficacy are shown in Table III:3- 2. Appendix III:3-4 contains information on points to be checked in a troublesome exhaust system. https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9734 https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10593 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 4 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html temperature rate of emission direction of emission initial emission velocity pattern of emission (continuous or intermittent) time intervals of emission mass of emitted material Air behavior Air temperature Air movement (direction, velocity) Mixing potential Supply and return flow conditions, to include pressure differences between space and surrounding areas Sources of tempered and untempered make-up air Air changes per hour Influence of existing HVAC systems Effects of wind speed and direction Effects of weather and season Employee Worker interaction with emission source Worker exposure levels Worker location Worker education, training, cooperation C. Basic Testing Equipment Basic testing equipment might include: smoke tubes velometers, anemometers: swinging vane anemometer thermal or hot-wire anemometer pressure-sensing devices: U-tube or electronic manometers Pitot tube thermal (thermal and swinging vane instruments measure static pressure indirectly) aneroid ("bellows") gauges noise-monitoring equipment measuring tapes other: rags, flashlight, mirror, tachometer combustible gas meter or oxygen meter tubes for CO, CO , formaldehyde, etc. D. Documentation The characteristics of the ventilation system that must be documented during an investigation include equipment operability, physical measurements of the system, and use practices. E. Equipment Operability Before taking velocity or pressure measurements, note and record the operating status of the equipment. For example, are filters loaded or clean? Are variable- flow devices like dampers, variable-frequency drives, or inlet vanes in use? Are make-up units operating? Are system blueprints available? F. Measurements 1. Duct diameters are measured to calculate duct areas. Inside duct diameter is the most important measurement, but an outside measurement is often sufficient for a sheet metal duct. To measure the duct, the tape should be thrown around the duct to obtain the duct circumference, and the number should be divided by (3.142) to obtain the diameter of the duct. 2. Hood and duct dimensions can be estimated from plans, drawings, and specifications. Measurements can be made with measuring tape. If a duct is constructed of 2½ or 4-foot sections, the sections can be counted (elbows and tees should be included in the length). 2 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 5 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html Figure III:3-2. Use of Smoke to Demonstrate Air Flow Velocity = Distance/Time, or V = D/T Figure III:3-3. Use of Static Pressure Tap Into Duct to Measure Hood Static Pressure 3. Hood-face velocities outside the hood or at the hood face can be estimated with velometers, smoke tubes, and swinging-vane anemometers, all of which are portable, reliable, and require no batteries. a. The minimum velocity that can be read by an anemometer is 50 feet per minute (fpm). The meter should always be read in the upright position, and only the tubing supplied with the equipment should be used. b. Anemometers often cannot be used if the duct contains dust or mist because air must actually pass through the instrument for it to work. The instrument requires periodic cleaning and calibration at least once per year. Hot-wire anemometers should not be used in airstreams containing aerosols. c. Hood-face velocity measurement involves the following steps: mark off imaginary areas; measure velocity at center of each area; and average all measured velocities. d. Smoke is useful for measuring face velocity (see Figure III:3-2) because it is visible. Nothing convinces management and employees more quickly that the ventilation is not functioning properly than to show smoke drifting away from the hood, escaping the hood, or traveling into the worker's breathing zone. Smoke can be used to provide a rough estimate of face velocity: Squeeze off a quick burst of smoke. Time the smoke plume's travel over a two-foot distance. Calculate the velocity in feet per minute. For example, if it takes two seconds for the smoke to travel two feet, the velocity is 60 fpm. 4. Hood static pressures (SPH) should be measured about 4-6 duct diameters downstream in a straight section of the hood take-off duct. The measurement can be made with a pitot tube or by a static pressure tap into the duct sheet metal (see Figure III:3-3) a. Pressure gauges come in a number of varieties, the simplest being the U-tube manometer. b. Inclined manometers offer greater accuracy and greater sensitivity at low pressures than U-tube manometers. However, manometers rarely can be used for velocities less than 800 fpm (i.e. velocity pressures less than 0.05" w.g.). Aneroid-type manometers use a calibrated bellows to measure pressures. They are easy to read and portable but require regular calibration and maintenance. 5. Duct velocity measurements may be made directly (with velometers and anemometers) or indirectly (with manometers and pitot tubes) using duct velocity pressure. a. Air flow in industrial ventilation ducts is almost always turbulent, with a small, nonmoving boundary layer at the surface of the duct. b. Because velocity varies with distance from the edge of the duct, a single measurement may not be sufficient. However, if the measurement is taken in a straight length of round duct, 4-6 diameters downstream and 2-3 diameters upstream from obstructions or directional changes, then the average velocity can be estimated at 90% of the centerline velocity. (The average velocity pressure is about 81% of centerline velocity pressure.) c. A more accurate method is the traverse method, which involves taking six or ten measurements on each of two or three passes across the duct, 90° or 60° opposed. Measurements are made in the center of concentric circles of equal area. d. Density corrections (e.g., temperature) for instrument use should be made in accordance with the manufacturer's instrument instruction manual and calculation/correction formulas. 6. Air cleaner and fan condition measurements can be made with a pitot tube and manometer. G. Good Practices 1. Hood placement must be close to the emission source to be effective. Maximum distance from the emission source should not exceed 1.5 duct diameters. a. The approximate relationship of capture velocity (V ) to duct velocity (V ) for a simple plain or narrow flanged hood is illustrated in Figure III:3-4. For example, if an emission source is one duct diameter in front of the hood and the duct velocity (V ) = 3,000 feet per minute (fpm), then the expected capture velocity (V ) is 300 fpm. At two duct diameters from the hood opening, capture velocity decreases by a factor of 10, to 30 fpm. c d d c 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 6 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html Figure III:3-4. Relationship of Capture Velocity (V ) to Duct Velocity (V ) Figure III:3-5. Rule of Thumb for Simple Capture Hoods: Maximum Capture Distance Should Not Be More Than 1.5 Times the Duct Diameter Figure III:3-6. Effective Flange Width (W) Figure III:3-7. An Illustration of the Six-and-Three Rule Figure III:3-8. Minimum Stack Height in Relation to Immediate Roof Line or Center of Any Air Intake on the Same Roof b. Figure III:3-5 shows a rule of thumb that can be used with simple capture hoods. If the duct diameter (D) is 6 inches, then the maximum distance of the emission source from the hood should not exceed 9 in. Similarly, the minimum capture velocity should not be less than 50 fpm. c. Figure III:3-6 provides a guide for determining an effective flange width. 2. System effect loss, which occurs at the fan, can be avoided if the necessary ductwork is in place. a. Use of the six-and-three rule ensures better design by providing for a minimum loss at six diameters of straight duct at the fan inlet and a minimum loss at three diameters of straight duct at the fan outlet (Figure II:3-7). b. System effect loss is significant if any elbows are connected to the fan at inlet or outlet. For each 2½ diameters of straight duct between the fan inlet and any elbow, CFM loss will be 20%. 3. Stack height should be 10 ft higher than any roof line or air intake located within 50 ft of the stack (Figure III:3-8). For example, a stack placed 30 ft away from an air intake should be at least 10 ft higher than the center of the intake. c d 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 7 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html Table III:3-3. Good Practices For Reviewing Plans and Specifications Investigate the background and objectives of the project. Understand the scope of the project. What is to be included and why? Look for conciseness and precision. Mark ambiguous phrases, "legalese," and repetition. Do the specifications spell out exactly what is wanted? What is expected? Do plans and specifications adhere to appropriate codes, standards, requirements,policies, and do they recommend good practice as established by the industry? Will the designer be able to design, or the contractor to build, the system from the plans and specifications? Will the project meet OSHA requirements if it is built as proposed? PUT IT ON PAPER 4. Ventilation system drawings and specifications usually follow standard forms and symbols, e.g., as described in the Uniform Construction Index (UCI). a. Plan sections include electrical, plumbing, structural, or mechanical drawings (UCI, Section 15). The drawings come in several views: plan (top), elevation (side and front), isometric, or section. b. Elevations (side and front views) give the most detail. An isometric drawing is one that illustrates the system in three dimensions. A sectional drawing provides duct or component detail by showing a cross-section of the component. c. Drawings are usually drawn to scale. (Check dimensions and lengths with a ruler or a scale to be sure that this is the case. For example, ⅛ inch on the sheet may represent one foot on the ground.) Good practices to follow when reviewing plans and specifications are listed in Table III:3-3. V. Prevention and Control A well-designed system and a continuing preventive maintenance program are key elements in the prevention and control of ventilation system problems. A. Elements of a Good Maintenance Program 1. Establish a safe place to file drawings, specifications, fan curves, operating instructions, and other papers generated during design, construction, and testing. 2. Establish a program of periodic inspection a. The types and frequencies of inspections depend on the operation of the system and other factors. Daily: Visual inspection of hoods, ductwork, access and clean-out doors, blast gate positions, hood static pressure, pressure drop across air cleaner, and verbal contact with users. ("How is the system performing today?") Weekly: Air cleaner capacity, fan housing, pulley belts. Monthly: Air cleaner components. b. A quick way to check for settled material in a duct is to take a broomstick and tap the underside of all horizontal ducts. If the tapping produces a "clean" sheet metal sound, the duct is clear. If the tapping produces heavy, thudding sounds and no sheet metal vibration, liquids or settled dust may be in the duct. 3. Establish a preventive maintenance program. Certain elements of any ventilation system should be checked on a regular schedule and replaced if found to be defective. 4. Provide worker training. Workers need to be trained in the purpose and functions of the ventilation system. For example, they need to know how to work safely and how best to utilize the ventilation system. Exhaust hoods do little good if the welder does not know that the hood must be positioned close to the work. 5. Keep written records. Maintain written documentation not only of original installations but also of all modifications as well as problems and their resolution. B. Dealing With Micro-Organisms 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 8 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html Table III:3-4. Preventive Measures for Reducing Microbial Problems in Buildings Prevent buildup of moisture in occupied spaces (relative humidity of 60% or less). Prevent moisture collection in HVAC components. Remove stagnant water and slime from mechanical equipment. Use steam for humidifying. Avoid use of water sprays in HVAC systems. Use filters with a 50-70% collection efficiency rating. Find and discard microbe-damaged furnishings and equipment. Provide regular preventive maintenance. If you suspect microbial agents, check for stagnant water in the ventilation system. The presence of mold or slime is a possible sign of trouble. Table III:3-4 lists preventive measures for controlling microbial problems in ventilation systems. C. Volatile Organic or Reactive Chemicals If an organic or reactive chemical (e.g., formaldehyde) is believed to be the primary agent in an IAQ problem, potential controls to consider include additional dilution ventilation, removal or isolation of the offending material, and the transfer of sensitized employees. D. Tobacco Smoke in Air OSHA has published a proposed rule for IAQ (including tobacco smoke in the workplace), and this rulemaking is likely to be completed in the near future. Smoking policies should include provisions for dedicated smoking areas. Dedicated smoking areas should be configured so that migration of smoke into nonsmoking areas will not occur. Such areas should: have floor-to-ceiling walls of tight construction; be under negative pressure relative to adjacent areas; AND be exhausted outside the building and not recirculated. For more information on investigation of complaints, CSHO's should consult the NIOSH Guidance for Indoor Air Quality Investigation and the EPA guide Building Air Quality (1991). VI. Bibliography American Conference of Governmental Industrial Hygienists (ACGIH). 1988. Industrial Ventilation, a Manual of Recommended Practice. 20th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists. Air Movement and Control Association (AMCA). 1988. AMCA Publication One. Arlington Heights, IL: Air Movement and Control Association. American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). Handbooks and Standards. Atlanta, GA: American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Sheet Metal and Air Conditioning Contractors National Association (SMACNA). SMACNA Publications. Arlington, VA: Sheet Metal and Air Conditioning Contractors National Association. American National Standards Institute (ANSI) Standards: Z9.1 - Open Surface Tanks Operation Z9.2 - Fundamentals Covering the Design and Operation of Local Exhaust Systems Z9.3 - Design, Construction, and Ventilation of Spray Finishing Operations Z9.4 - Ventilation and Safe Practice of Abrasive Blasting Operations Z9.5 - Laboratory Ventilation. Fairfax, VA: American Industrial Hygiene Association. Burgess, W. A. et al. 1989. Ventilation and Control of the Work Environment. New York: Wiley Interscience. Burton, D. J. 1989. Industrial Ventilation Workbook. Salt Lake City, UT: IVE, Inc. Burton, D. J. 1990. Indoor Air Quality Workbook. Salt Lake City, UT: IVE, Inc. Jorgensen, R. et al. 1983. Fan Engineering. 8th ed. Buffalo, NY: Buffalo Forge Co. Homeon, W. C. L. 1963. Plant and Process Ventilation. New York: Industrial Press. National Institute for Occupational Safety and Health (NIOSH). 1987. Guidance for Indoor Air Quality Investigations. Cincinnati: NIOSH. OSHA Field Operations Manual. 1992. OSHA Instruction CPL 2.45B. Washington, D.C.: U.S. Government Printing Office. U.S. Environmental Protection Agency (EPA). 1991. Building Air Quality. Appendix III:3-1. Ventilation Primer 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 9 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html Table III:3-5. Selection Criteria for General and Local Exhaust Systems General exhaust ventilation (dilution ventilation) is appropriate when: Emission sources contain materials of relatively low hazard. (The degree of hazard is related to toxicity, dose rate, and individual susceptibility); Emission sources are primarily vapors or gases, or small, respirable-size aerosols (those not likely to settle); Emissions occur uniformly; Emissions are widely dispersed; Moderate climatic conditions prevail; Heat is to be removed from the space by flushing it with outside air; Concentrations of vapors are to be reduced in an enclosure; and Portable or mobile emission sources are to be controlled. Local exhaust ventilating is appropriate when: Emission sources contain materials of relatively high hazard; Emitted materials are primarily larger-diameter particulates (likely to settle); Emissions vary over time; Emission sources consist of point sources; Employees work in the immediate vicinity of the emission source; The plant is located in a severe climate; and Minimizing air turnover is necessary. where: q = evaporation rate in acfm 387 = volume in cubic feet formed by the evaporation of one lb-mole of a substance, e.g., a solvent MW = molecular weight of emitted material lbs = lbs of material evaporated min = time of evaporation d = density correction factor where: Q = volume flow rate of air, in acfm q = evaporation rate, in acfm K = mixing factor to account for poor or random mixing (NOTE: K = 2 to 5; K = 2 is optimum) C = acceptable airborne concentration of the material (typically half of the PEL). Selection Before an appropriate ventilation system can be selected, the employer should study emission sources, worker behavior, and air movement in the area. In some cases the employer may wish to seek the services of an experienced professional ventilation engineer to assist in the data gathering. Table III:3-5 shows factors to consider when selecting a ventilation system. Combinations of controls are often employed for HVAC purposes. General Exhaust (Dilution) Ventilation Systems General exhaust ventilation, also called dilution ventilation, is different from local exhaust ventilation because instead of capturing emissions at their source and removing them from the air, general exhaust ventilation allows the contaminant to be emitted into the workplace air and then dilutes the concentration of the contaminant to an acceptable level (e.g., to the PEL or below). Dilution systems are often used to control evaporated liquids. To determine the correct volume flow rate for dilution (Q ), it is necessary to estimate the evaporation rate of the contaminant (q ) according to the following equation: q = [(387)(lbs)]/[(MW)(min)(d)] The appropriate dilution volume flow rate for toxics is: Q = [(q )(K )(10 )]/C The number of air changes per hour is the number of times one volume of air is replaced in the space per hour. In practice, replacement depends on mixing efficiency. When using dilution ventilation: position exhausts as close to emission sources as possible; use auxiliary fans for mixing; d d d d d d m 6 a d d m m m a 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 10 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html where: K = loss factor VP = velocity pressure in duct |SP | = absolute static pressure about 5 duct diameters down the duct from the hood. C =Q =√VP =√1 Q SP 1 + K where: K = loss factor VP = velocity pressure in duct SP = absolute static pressure about 5 duct diameters down the duct from the hood. make sure employees are upwind of the dilution zone; and add make-up air where it will be most effective. Local Exhaust Ventilation Systems A typical local exhaust ventilation system is composed of five parts: fans, hoods, ducts, air cleaners, and stacks. Local exhaust ventilation is designed to capture an emitted contaminant at or near its source, before the contaminant has a chance to disperse into the workplace air. Fan Selection. To choose the proper fan for a ventilation system, this information must be known: air volume to be moved; fan static pressure; type and concentration of contaminants in the air (because this affects the fan type and materials of construction); and the importance of noise as a limiting factor. Once this information is available, the type of fan best suited for the system can be chosen. Many different fans are available, although they all fall into one of two classes: axial flow fans and centrifugal fans. For a detailed explanation of fans, see the ACGIH Industrial Ventilation Manual. Hoods. The hood captures, contains, or receives contaminants generated at an emission source. The hood converts duct static pressure to velocity pressure and hood entry losses (e.g., slot and duct entry losses). Hood entry loss (H ) is calculated according to the following equation: H = (K)(VP) = |SP | = VP A hood's ability to convert static pressure to velocity pressure is given by the coefficient of entry (C ), as follows: To minimize air-flow requirements, the operation should be enclosed as much as possible, either with a ventilated enclosure, side baffles, or curtains. This helps both to contain the material and to minimize the effect of room air. When using a capture or receiving hood, the hood should be located as close to the contaminant source as possible. Reducing the amount of contaminants generated or released from the process reduces ventilation requirements. The hood should be designed to achieve good air distribution into the hood openings so that all the air drawn into the hood helps to control contaminants. Avoid designs that require that the velocities through some openings be very high in order to develop the minimum acceptable velocity through other openings or parts of the hood. The purpose of most ventilation systems is to prevent worker inhalation of contaminants. For this reason, the hood should be located so that contaminants are not drawn through the worker's breathing zone. This is especially important where workers lean over an operation such as an open-surface tank or welding bench. Hoods must meet the design criteria in the ACGIH Industrial Ventilation Manual or applicable OSHA standards. Most hood design recommendations account for cross-drafts that interfere with hood operation. Strong cross-drafts can easily reduce a hood's effectiveness by 75%. Standard hood designs may not be adequate to contain highly toxic materials. The hood should be designed to cause minimum interference with the performance of work. Positioning access doors inside an enclosure that must be opened and closed often means that in practice the doors will be left open, and locating capture hoods too close to the process for the worker's convenience often means that the hood will be disassembled and removed. Hoods should never increase the likelihood of mechanical injury by interfering with a worker's freedom to move around machinery. Two common misconceptions about hoods that are a part of local exhaust systems are: Hoods draw air from a significant distance away from the hood opening, and therefore they can control contaminants released some distance away. It is easy to confuse a fan's ability to blow a jet of air with its ability to draw air into a hood. Hoods must be close to the source of contamination to be effective. e e h h e e ideal actual h h 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 11 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html Heavier-than-air vapors tend to settle to the workroom floor and therefore can be collected by a hood located there. A small amount of contaminant in the air (1,000 ppm means 1,000 parts of contaminant plus 999,000 parts of air) has a resulting density close to that of air, and random air currents will disperse the material throughout the room. Ducts. Air flows turbulently through ducts at between 2,000-6,000 feet per minute (fpm). Ducts can be made of galvanized metal, fiberglass, plastic, and concrete. Friction losses vary according to ductwork type, length of duct, velocity of air, duct area, density of air, and duct diameter. Air Cleaners. The design of the air cleaner depends on the degree of cleaning required. Regular maintenance of air cleaners increases their efficiency and minimizes worker exposure. Different types of air cleaners are made to remove particulates (e.g., precipitators, cyclones, etc.) and gases and vapors (e.g., scrubbers). Stacks. Stacks disperse exhaust air into the ambient environment. The amount of reentrainment depends on exhaust volume, wind speed and direction, temperature, location of intakes and exhausts, etc. When installing stacks: Provide ample stack height (a minimum of 10 ft above adjacent rooflines or air intakes); Place stack downwind of air intakes; Provide a stack velocity of a minimum of 1.4 times the wind velocity; Place the stack as far from the intake as possible (50 ft is recommended); Place the stack at least 10 ft high on most roofs to avoid recirculation; and Avoid rain caps if the air intake is within 50 ft of the stack. Make-up Air Systems Exhaust ventilation systems require the replacement of exhausted air. Replacement air is often called make-up air. Replacement air can be supplied naturally by atmospheric pressure through open doors, windows, wall louvers, and adjacent spaces (acceptable), as well as through cracks in walls and windows, beneath doors, and through roof vents (unacceptable). Make-up air can also be provided through dedicated replacement air systems. Generally, exhaust systems are interlocked with a dedicated make-up air system. Other reasons for designing and providing dedicated make-up air systems are that they: Avoid high-velocity drafts through cracks in walls, under doors, and through windows; Avoid differential pressures on doors, exits, and windows; and Provide an opportunity to temper the replacement air. If make-up air is not provided, a slight negative pressure will be created in the room and air flow through the exhaust system will be reduced. HVAC HVAC (heating, ventilating, and air-conditioning) is a common term that can also include cooling, humidifying or dehumidifying, or otherwise conditioning air for comfort and health. HVAC also is used for odor control and the maintenance of acceptable concentrations of carbon dioxide. Air-conditioning has come to include any process that modifies the air for a work or living space: heating or cooling, humidity control, and air cleaning. Historically, air-conditioning has been used in industry to improve or protect machinery, products, and processes. The conditioning of air for humans has become normal and expected. Although the initial costs of air conditioning are high, annual costs may account only for about 1% to 5% of total annual operating expenses. Improved human productivity, lower absenteeism, better health, and reduced housekeeping and maintenance almost always make air-conditioning cost effective. Mechanical air-handling systems can range from simple to complex. All distribute air in a manner designed to meet ventilation, temperature, humidity, and air- quality requirements established by the user. Individual units may be installed in the space they serve, or central units can serve multiple areas. HVAC engineers refer to the areas served by an air handling system as zones. The smaller the zone, the greater the likelihood that good control will be achieved; however, equipment and maintenance costs are directly related to the number of zones. Some systems are designed to provide individual control of rooms in a multiple-zone system. Both the provision and distribution of make-up air are important to the proper functioning of the system. The correct amount of air should be supplied to the space. Supply registers should be positioned to avoid disruption of emission and exposure controls and to aid dilution efforts. Considerations in designing an air-handling system include volume flow rate, temperature, humidity, and air quality. Equipment selected must be properly sized and may include: outdoor air plenums or ducts filters supply fans and supply air systems heating and cooling coils humidity control equipment supply ducts distribution ducts, boxes, plenums, and registers dampers return air plenums 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 12 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html Table III:3-6. Recirculation Criteria Protection of employees must be the primary design consideration. The system should remove as much of the contaminant as can economically be separated from exhaust air. The system should not be designed simply to achieve PEL levels of exposure. The system should never allow recirculation to significantly increase existing exposures. Recirculation should not be used if a carcinogen is present. The system should have fail-safe features, e.g., warning devices on critical parts, back-up systems. Cleaning and filtering devices that ensure continuous and reliable collection of the contaminant should be used. The system should provide a by-pass or auxiliary exhaust system for use during system failure. The system should include feedback devices that monitor system performance, e.g., static pressure taps, particulate counters, amperage monitors. The system should be designed not to recirculate air during equipment malfunction. The employer should train employees in the use and operation of the system. acfm Actual cubic feet per minute of gas flowing at existing temperature and pressure. (See also scfm.) ACH, AC/H (air changes per hour) The number of times air is replaced in an hour. Air Density The weight of air in lbs per cubic foot. Dry standard air at T=68° F (20° C) and BP = 29.92 in Hg (760 mm Hg) has a density of 0.075 lb/cu ft. Anemometer A device that measures the velocity of air. Common types include the swinging vane and the hot-wire anemometer. Area (A) The cross-sectional area through which air moves. Area may refer to the cross-sectional area of a duct, a window, a door, or any space through which air moves. Atmospheric Pressure The pressure exerted in all directions by the atmosphere. At sea level, mean atmospheric pressure is 29.92 in Hg, 14.7 psi, 407 in w.g., or 760 mm Hg. Brake Horsepower (bhp) The actual horsepower required to move air through a ventilation system against a fixed total pressure plus the losses in the fan. bhp=ahp x 1/eff, where eff is fan mechanical efficiency. Branch In a junction of two ducts, the branch is the duct with the lowest volume flow rate. The branch usually enters the main at an angle of less than 90. Canopy Hood (Receiving Hood) A one- or two-sided overhead hood that receives rising hot air or gas. Capture Velocity in. w.g. (inches of water) A unit of pressure. One inch of water is equal to 0.0735 in. of mercury, or 0.036 psi. Atmospheric pressure at standard conditions is 407 in. w.g. Industrial Ventilation (IV) The equipment or operation associated with the supply or exhaust of air by natural or mechanical means to control occupational hazards in the industrial setting. Laminar Flow (also Streamline Flow) Air flow in which air molecules travel parallel to all other molecules; laminar flow is characterized by the absence of turbulence. Local Exhaust Ventilation An industrial ventilation system that captures and removes emitted contaminants before dilution into the ambient air of the workplace. Loss Usually refers to the conversion of static pressure to heat in components of the ventilation system, e.g., "the hood entry loss." Make-Up Air See Replacement and Compensating Air. Manometer A device that measures pressure difference; usually a U-shaped glass tube containing water or mercury. Minimum Transport Velocity (MTV) The minimum velocity that will transport particles in a duct with little settling; MTV varies with air density, particulate loading, and other factors. Outdoor Air (OA) Outdoor air is the "fresh" air mixed with return air (RA) to dilute contaminants in the supply air. Pitot Tube exhaust air provisions return fans controls and instrumentation Recirculation Although not generally recommended, recirculation is an alternative to air exchanging. Where used, recirculation should incorporate air cleaners, a by-pass or auxiliary exhaust system, regular maintenance and inspection, and devices to monitor system performance. Key points to consider in the use of recirculation are shown in Table III:3-6. Appendix III:3-2. Glossary 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 13 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html The velocity of air induced by a hood to capture emitted contaminants external to the hood. Coefficient of Entry (C ) A measure of the efficiency of a hood's ability to convert static pressure to velocity pressure; the ratio of actual flow to ideal flow. Density Correction Factor A factor applied to correct or convert dry air density of any temperature to velocity pressure; the ratio of actual flow to ideal flow. Dilution Ventilation (General Exhaust Ventilation) A form of exposure control that involves providing enough air in the workplace to dilute the concentration of airborne contaminants to acceptable levels. Entry Loss See Hood Entry Loss or Branch Entry Loss. Evase (pronounced eh-va-say) A cone-shaped exhaust stack that recaptures static pressure from velocity pressure. Fan A mechanical device that moves air and creates static pressure. Fan Laws Relationships that describe theoretical, mutual performance changes in pressure, flow rate, rpm of the fan, horsepower, density of air, fan size, and sound power. Fan Curve A curve relating pressure and volume flow rate of a given fan at a fixed fan speed (rpm). Friction Loss The static pressure loss in a system caused by friction between moving air and the duct wall, expressed as in w.g./100 ft, or fractions of VP per 100 ft of duct (mm w.g./m; Kpa/m). Gauge Pressure The difference between two absolute pressures, one of which is usually atmospheric pressure. General Exhaust See Dilution Ventilation. Head Pressure, e.g. "The head is 1 in w.g." Hood A device that encloses, captures, or receives emitted contaminants. Hood Entry Loss (H ) The static pressure lost (in inches of water) when air enters a duct through a hood. The majority of the loss usually is associated with a vena contracta formed in the duct. Hood Static Pressure (SP ) The sum of the duct velocity pressure and the hood entry loss; hood static pressure is the static pressure required to accelerate air at rest outside the hood into the duct at velocity. HVAC (Heating, Ventilation, and Air Conditioning) Systems Ventilating systems designed primarily to control temperature, humidity, odors, and air quality. Indoor Air Quality (IAQ), Sick-Building Syndrome, Tight-Building Syndrome The study, examination, and control of air quality related to temperature, humidity, and airborne contaminants. A device used to measure total and static pressures in an airstream. Plenum A low-velocity chamber used to distribute static pressure throughout its interior. Pressure Drop The loss of static pressure across a point; for example, "the pressure drop across an orifice is 2.0 in. w.g." Replacement Air (also, Compensating Air, Make-Up Air) Air supplied to a space to replace exhausted air. Return Air Air that is returned from the primary space to the fan for recirculation. scfm Standard cubic feet per minute. A measure of air flow at standard conditions, i.e., dry air at 29.92 in. Hg (760 mm Hg) (gauge), 68° F (20° C). Slot Velocity The average velocity of air through a slot. Slot velocity is calculated by dividing the total volume flow rate by the slot area (usually, Vs = 2,000 fpm). Stack A device on the end of a ventilation system that disperses exhaust contaminants for dilution by the atmosphere. Standard Air, Standard Conditions Dry air at 68° F (20° C), 29.92 in Hg (760 mm Hg). Static Pressure (SP) The pressure developed in a duct by a fan; the force in inches of water measured perpendicular to flow at the wall of the duct; the difference in pressure between atmospheric pressure and the absolute pressure inside a duct, cleaner, or other equipment; SP exerts influence in all directions. Suction Pressure (See Static Pressure.) An archaic term that refers to static pressure on the upstream side of the fan. Total Pressure The pressure exerted in a duct, i.e., the sum of the static pressure and the velocity pressure; also called Impact Pressure, Dynamic Pressure. Transport Velocity See Minimum Transport Velocity. Turbulent Flow Air flow characterized by transverse velocity components as well as velocity in the primary direction of flow in a duct; mixing velocities. Velocity (V) The time rate of movement of air; usually expressed as feet per minute. Velocity Pressure (VP) The pressure attributed to the velocity of air. Volume Flow Rate (Q) Quantity of air flow in cfm, scfm, or acfm. Appendix III:3-3. OSHA and Consensus Standards e e h 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 14 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html 29 CFR 1910.94(a) Abrasive blasting 29 CFR 1910.94(b) Grinding, polishing, and buffing operations 29 CFR 1910.94(d) Open surface tanks 29 CFR 1910.252(c)(2)(i)(a) and (b); (c)(2)(ii) Ventilation for general welding and cutting--General 29 CFR 1910.252(c)(3) Local exhaust hoods and booths 29 CFR 1910.252(c)(5)(ii) Fluorine compounds--Maximum allowable concentration 29 CFR 1910.252(c)(12) Cutting of stainless steels 29 CFR 1910.1003 to .1016 Carcinogens 29 CFR 1910.1025(e)(5) Lead 29 CFR 1910.1027(f)(3) Cadmium 29 CFR 1926.27(a) Ventilation--General 29 CFR 1926.62(e)(3) Lead 29 CFR 1926.63(f)(4) Cadmium 29 CFR 1926.154(a)(1) Temporary heating devices--Ventilation 29 CFR 1926.353(e)(1) Ventilation and protection in welding, cutting and h eating-- Gal welding, cutting, and heating 29 CFR 1915.32(a)(2) Toxic cleaning solvents 29 CFR 1915.51(f)(1) Ventilation and protection in welding, cutting, and heating-- General welding, cutting, and heating 29 CFR 1918.93(a)(1)(iii) Ventilation and atmospheric conditions 29 CFR 1910.94(a)(3)(i)(d) Abrasive blasting--Blasting cleaning 29 CFR 1910.94(a)(5) Abrasive blasting--Personal protective equipment 29 CFR 1910.94(a)(6) Abrasive blasting--Air supply and air compressors 29 CFR 1910.94(a)(7) Abrasive blasting--Operational procedures and general safety I. OSHA Standards A. Health-Related Ventilation Standards. This list includes some, but not necessarily all, OSHA standards that address the control of employee exposure to recognized contaminants.) General Industry Construction Maritime B. Health-Related Ventilation Standards Other Than Airflow. This list includes some, but not necessarily all, OSHA standards that do not contain airflow requirements but are located in the health-related ventilation standards. General Industry 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 15 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html 29 CFR 1910.94(d)(9) Open surface tanks--Personal protection 29 CFR 1910.94(d)(10) Open surface tanks--Special precautions for cyanide 29 CFR 1910.94(d)(11) Open surface tanks--Inspection, installation and maintenance 29 CFR 1910.94(d)(12) Open surface tanks--Vapor degreasing tanks 29 CFR 1910.94(c) Ventilation--Spray finishing operations 29 CFR 1910.103(b)(3)(ii)(b) Hydrogen--Gaseous hydrogen systems--Separate buildings 29 CFR 1910.103(b)(3)(iii)(b) Hydrogen--Gaseous hydrogen systems--Special rooms 29 CFR 1910.103(c)(3)(ii)(b) Hydrogen--Liquid hydrogen systems--Separate buildings 29 CFR 1910.103(c)(3)(iii)(b) Hydrogen--Liquid hydrogen systems--Special rooms 29 CFR 1910.104(b)(3)(xii) Oxygen--Bulk oxygen systems--Ventilation 29 CFR 1910.104(b)(8)(vii) Oxygen--Bulk oxygen systems--Venting 29 CFR 1910.106(d)(4)(iv) Flammable and combustible liquids--Container and portable tank storage--Design and construction of inside storage room- -Ventilation 29 CFR 1910.106(e)(3)(v) Flammable and combustible liquids--Industrial plants--Unit physical operations--Ventilation 29 CFR 1910.106(f)(2)(iii)(a) Flammable and combustible liquids--Bulk plants--Building-- Ventilation 29 CFR 1910.106(h)(3)(iii) Flammable and combustible liquids--Processing plants-- Processing building--Ventilation 29 CFR 1910.107(b)(5)(i) Spray finishing using flammable and combustible materials-- Spray booths--Dry type overspray collectors 29 CFR 1910.107(d)(1) and (2) Spray finishing using flammable and combustible materials-- Ventilation--Conformance--General 29 CFR 1910.107(i)(9) Spray finishing using flammable and combustible materials-- Electrostatic hand spraying equipment--Ventilation 29 CFR 1910.108(b)(1) and (2) Dip tanks containing flammable combustible liquids-- Ventilation--Ventilation combined with drying 29 CFR 1910.307 Hazardous (classified) locations 29 CFR 1915.12(a)(2) Precautions before entering--Flammable atmospheres and residues 29 CFR 1915.13(a)(2) Cleaning and other cold work (flammable vapors) C. Fire and Explosion-Related Ventilation Standards. This list includes some, but not necessarily all, OSHA standards that are intended to prevent fire and explosions. General Industry D. Exceptions to 25% of the LEL for Fire and Explosion-Related Standards. This list includes but is not limited to OSHA standards that allow concentrations of flammable materials no greater than 10% of the LEL. Maritime 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 16 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html 29 CFR 1915.35(b)(1), (2), (3) Painting--Paints and tanks coatings dissolved in highly volatile, toxic and/or flammable solvents 29 CFR 1915.36(a)(2) Flammable liquids ventilation 29 CFR 1926.803(i)(2) Compressed Air--Ventilation and air quality--(Tunnels) 29 CFR 1910.252(c)(2)(i)(c) Welding, cutting and brazing--Health protection and ventilating--Ventilation for general welding and cutting-- General 29 CFR 1910.252(c)(4) Welding, cutting and brazing--Health protection and ventilating--Ventilation in confined spaces 29 CFR 1910.252(c)(5)(i) Welding, cutting and brazing--Fluorine compounds 29 CFR 1910.252(c)(6)(i) Welding, cutting and brazing--Zinc--Confined spaces 29 CFR 1910.252(c)(7)(i) Welding, cutting and brazing--Lead--Confined spaces 29 CFR 1910.252(c)(8) Welding, cutting and brazing--Beryllium 29 CFR 1910.252(c)(9) Welding, cutting and brazing--Cadmium 29 CFR 1910.252(c)(10) Welding, cutting and brazing--Mercury 29 CFR 1926.154(a)(2) Temporary heating devices--Ventilation 29 CFR 1926.353(b)(1) Ventilation and protection in welding, cutting and heating-- Welding, cutting and heating in confined spaces 29 CFR 1926.353(c)(1) and (2) Ventilation and protection in welding, cutting and heating-- Welding, cutting or heating of metals of toxic significance 29 CFR 1926.800(k) Tunnels and shafts--Air quality and ventilation 29 CFR 1915.12(b)(2) Precautions before entering--Toxic atmospheres and residues 29 CFR 1915.12(c)(2) Precautions before entering--Oxygen deficient atmospheres 29 CFR 1915.12(d) Precautions before entering--Exceptions 29 CFR 1915.34(a)(4) Mechanical paint removers--Power tools--(paint dust) 29 CFR 1915.51(c)(3) Ventilation and protection in welding, cutting and heating-- Welding, cutting and heating confined spaces 29 CFR 1915.51(d)(1) and (2) Ventilation and protection in welding, cutting and heating-- cutting or heating of metals of toxic significance. Standard Source Title Construction E. Special Conditions Standards. This list includes some but not necessarily all OSHA standards that involve confined space operations and/or high- hazard contaminants specifically designated in the standard. General Industry Construction Maritime II. Consensus Standards 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 17 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html Air filters ASHRAE 52-76 ASHRAE Methods of Testing Air-Cleaning Devices Used in General Ventilation for Removing Particulate Matter Exhaust systems ANSI Z33.1- 1982 NFPA 91-1983 NFPA Installation of Blower and Exhaust Systems for Dust, Stock, Vapor Removal or Conveying (1983) ANSI Z9.2- 1979 AIHA Fundamentals Governing the Design and Operation of Local Exhaust Systems ANSI Z9.1- 1977 AIHA ASHRAE Practices for Ventilation and Operation of Open-Surface Tanks ANSI Z9.3- 1964 ANSI Safety Code for Design, Construction, and Ventilation of Spray Finishing Operations (reaffirmed 1971) ANSI Z9.4- 1979 ANSI Z9.4A- 1981 ANSI Ventilation and Safe Practices of Abrasives Blasting Operations ANSI Z9.5- 1992 AIHA Laboratory Ventilation Fans AMCA 99-83 ANSI/UL 507- 1976 AMCA UL Standards Handbook Electric Fans (1977) ASHRAE 51-75 AMCA 210-74 ASHRAE Laboratory Methods of Testing Fans for Rating ANSI/ASHRAE 87.7-1983 ASHRAE Methods of Testing Dynamic Characteristics of Propeller Fans-- Aerodynamically Excited Fan Vibrations and Critical Speeds AMCA 210-74 AMCA Laboratory Methods of Testing Fans for Rating Purposes AMCA 99- 2404-78 AMCA Drive Arrangement for Centrifugal Fans AMCA 99- 2406-83 AMCA Designation for Rotation and Discharge of Centrifugal Fans AMCA 99- 2407-66 AMCA Motor Positions for Belt or Chain Drive Centrifugal Fans AMCA 99- 2410-82 AMCA Drive Arrangement for Tubular Centrifugal Fans Industrial Duct SMACNA SMACNA Round Industrial Duct Construction SMACNA SMACNA Rectangular Industrial Duct Construction Venting NFPA 68 NFPA Guide for Explosion Venting NFPA 204M NFPA Guide for Smoke and Heat Venting SMACNA SMACNA Guide for Steel Stack Design and Construction (1983) Ventilation NFPA 96 NFPA Vapor Removal from Cooking Equipment (1984) 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 18 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html NFPA-88A, 88B NFPA Parking Structures (1979); Repair Garages (1979) ASHRAE 62- 1989 ASHARAE Ventilation for Acceptable Indoor Air Quality ACGIH ACGIH Industrial Ventilation Source Organization ACGIH American Conference of Governmental Industrial Hygienists 6500 Glenway Ave., Bldg. D-5 Cincinnati, OH 45211 AIHA American Industrial Hygiene Association 2700 Prosperity Ave., Suite 250 Fairfax, VA 22031-4319 AMCA Air Movement and Control Association 30 W. University Dr. Arlington Heights, IL 60004 ANSI American National Standards Institute 1430 Broadway New York, NY 10018 ASHRAE American Society of Heating, Refrigeration and Air-Conditioning Engineers, Inc. 1791 Tullie Circle, N.E., Atlanta, GA 30329 NFPA National Fire Protection Association Batterymarch Park Quincy, MA 02269 SMACNA Sheet Metal and Air Conditioning Contractors' National Association 8224 Old Courthouse Rd. Vienna, VA 22180 UL Underwriters Laboratories Inc. 333 Pfingsten Rd. Northbrook, IL 60062 III. Sources of Consensus Standards Copies of the consensus standards are published and available directly from the organization issuing the standard. A minimal fee is often required. Appendix III:3-4. Troubleshooting an Exhaust System--Some Helpful Hints Most of the following checks can be made by visual observation and do not require extensive measurements. If air flow is low in hoods, check: Fan rotation (reversed polarity will cause fan to run backwards; a backward-running centrifugal fan delivers only 30-50% of rated flow); Fan RPM; Slipping belt; Clogged or corroded fan wheel and casing; Clogged ductwork (high hood static pressure and low air flow may indicate restricted ducts; open clean-out doors and inspect inside ducts); Closed dampers in ductwork; Clogged collector or air cleaning devices; Weather cap too close to discharge stack (a ¾ duct- diameter gap should exist between cap and stack; weather caps are not recommended); Poorly designed ductwork (short radius elbows); (branch entries enter main duct at sharp angles); (ductwork diameter too small for the air-flow needed; and Lack of make-up air (high negative pressures affect propeller fan system output; lack of supplied make-up air causes high airflow velocities at doors and windows). If air flow is satisfactory in a hood but contaminant control is poor, check: 1/20/20, 12:20 PMOSHA Technical Manual (OTM) | Section III: Chapter 3: Ventilation Investigation | Occupational Safety and Health Administration Page 19 of 19https://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_3.html UNITED STATES DEPARTMENT OF LABOR Occupational Safety and Health Administration 200 Constitution Ave NW Washington, DC 20210 ' 800-321-6742 (OSHA) TTY www.OSHA.gov FEDERAL GOVERNMENT White House Severe Storm and Flood Recovery Assistance Disaster Recovery Assistance DisasterAssistance.gov USA.gov No Fear Act Data U.S. Office of Special Counsel OCCUPATIONAL SAFETY AND HEALTH Frequently Asked Questions A - Z Index Freedom of Information Act Read the OSHA Newsletter Subscribe to the OSHA Newsletter OSHA Publications Office of Inspector General ABOUT THE SITE Freedom of Information Act Privacy & Security Statement Disclaimers Important Website Notices Plug-Ins Used by DOL Accessibility Statement Crossdrafts (from process air movements); (worker-cooling fans and air-supply systems); (open doors and windows); Capture velocity (work operation too far from hood opening); Hood enclosure: (door, baffles, or sides may be open or removed); and Hood type: (canopy hoods are inappropriate for toxic materials). tel:800-321-6742 https://www.dol.gov/general/contact-phone-call-center%23tty https://www.osha.gov/ https://www.whitehouse.gov/ https://www.dol.gov/general/stormrecovery https://www.dol.gov/general/disasterrecovery https://www.disasterassistance.gov/ https://www.usa.gov/ https://www.dol.gov/agencies/oasam/civil-rights-center/resports/notification-and-federal-employee-antidiscrimination-retaliation-act-of-2002 https://osc.gov/ https://www.osha.gov/faq https://www.osha.gov/a-z https://www.osha.gov/foia https://www.osha.gov/quicktakes https://www.osha.gov/quicktakes/%23subscribe https://www.osha.gov/pls/publications/publication.html https://www.oig.dol.gov/ https://www.dol.gov/general/foia https://www.dol.gov/general/privacynotice https://www.dol.gov/general/disclaim https://www.dol.gov/general/aboutdol/website-policies https://www.dol.gov/general/aboutdol/file-formats https://www.dol.gov/general/aboutdol/accessibility
1/20/20, 12:19 PMSafety and Health Topics | Chemical Hazards and Toxic Substances - Controlling Exposure | Occupational Safety and Health Administration Page 1 of 2https://www.osha.gov/SLTC/hazardoustoxicsubstances/control.html UNITED STATES DEPARTMENT OF LABOR ! " # $ % & Controlling Exposure The following references aid in controlling workplace hazards associated with chemical hazards and toxic substances. Overview of Controls Controlling exposures to chemical hazards and toxic substances is the fundamental method of protecting workers. A hierarchy of controls is used as a means of determining how to implement feasible and effective controls. OSHA’s longstanding policy is that engineering and work practice controls must be the primary means used to reduce employee exposure to toxic chemicals, as far as feasible, and that respiratory protection is required to be used when engineering or work practice controls are infeasible or while they are being implemented. Where possible, elimination or substitution is the most desirable followed by engineering controls. Administrative or work practice controls may be appropriate in some cases where engineering controls cannot be implemented or when different procedures are needed after implementation of the new engineering controls. Personal protection equipment is the least desirable but may still be effective. Type of Control Examples Elimination/Substitution Substitute with safer alternatives. [See Transitioning to Safer Chemicals: A Toolkit for Employers and Workers] Engineering Controls (implement physical change to the workplace, which eliminates/reduces the hazard on the job/task) Change process to minimize contact with hazardous chemicals. Isolate or enclose the process. Use of wet methods to reduce generation of dusts or other particulates. General dilution ventilation. Use fume hoods. Administrative and Work Practice Controls (establish efficient processes or procedures) Rotate job assignments. Adjust work schedules so that workers are not overexposed to a hazardous chemical. Personal Protective Equipment (use protection to reduce exposure to risk factors) Use chemical protective clothing. Wear respiratory protection. [See the Respiratory Safety and Health Topics / Chemical Hazards and Toxic Substances Chemical Hazards and Toxic Substances Occupational Safety and Health Administration CONTACT US FAQ A TO Z INDEX ENGLISH ESPAÑOL OSHA STANDARDS TOPICS HELP AND RESOURCES https://www.dol.gov/ https://www.facebook.com/departmentoflabor https://twitter.com/OSHA_DOL https://www.instagram.com/USDOL/ https://www.osha.gov/rss/ https://www.osha.gov/quicktakes%23subscribe https://www.youtube.com/user/USDepartmentofLabor/ https://www.osha.gov/dsg/safer_chemicals/index.html https://www.osha.gov/SLTC/respiratoryprotection/index.html https://www.osha.gov/SLTC/text_index.html https://www.osha.gov/ https://www.osha.gov/contactus https://www.osha.gov/faq https://www.osha.gov/a-z javascript:doGTranslate('en%7Cen') javascript:doGTranslate('en%7Ces') https://www.osha.gov/aboutosha https://www.osha.gov/laws-regs https://www.osha.gov/SLTC/ https://www.osha.gov/news 1/20/20, 12:19 PMSafety and Health Topics | Chemical Hazards and Toxic Substances - Controlling Exposure | Occupational Safety and Health Administration Page 2 of 2https://www.osha.gov/SLTC/hazardoustoxicsubstances/control.html Protection Safety and Health Topics page] Use gloves. Wear eye protection. Additional Information Permissible Exposure Limits - Annotated Tables. OSHA, (2013). OSHA has annotated the existing Z-Tables with other selected occupational exposure limits. OSHA has chosen to present a side-by-side table with the Cal/OSHA PELs, the NIOSH Recommended Exposure Limits (RELs) and the ACGIH® TLVs®s which provides employers, workers, and other interested parties a list of alternate occupational exposure limits that may serve to better protect workers. Hazard Communication. OSHA Safety and Health Topics Page. Provides example HazCom programs, many training resources, as well as links to the proposed Globally Harmonized System of Classification and Labeling of Chemicals (GHS). Hazard Communication: Small Entity Compliance Guide for Employers That Use Hazardous Chemicals. OSHA Publication 3695, (2014). Process Safety Management. OSHA Safety and Health Topics Page. Contains requirements for the management of hazards associated with processes using highly hazardous chemicals included in the Process Safety Management of Highly Hazardous Chemicals Standard (29 CFR 1910.119). Sampling and Analysis. OSHA Safety and Health Topics Page. Describes chemical sampling and analysis used by occupational and safety professionals to assess workplace contaminants and associated worker exposures. Chemical Safety. National Institute for Occupational Safety and Health (NIOSH) Workplace Safety and Health Topic. Provides information on many hazardous chemicals and chemical concerns. Recommendations for Chemical Protective Clothing: A Companion to the NIOSH Pocket Guide to Chemical Hazards. National Institute for Occupational Safety and Health (NIOSH). Identifies protective clothing materials appropriate for chemicals listed in this pocket guide. A Guide for Evaluating the Performance of Chemical Protective Clothing. U.S. Department of Health and Human Services (DHHS), National Institute for Occupational Safety and Health (NIOSH) Publication No. 90-109, (June 1990). Includes selection and evaluation guidelines for protective clothing. Report To Congress On Workers' Home Contamination Study Conducted Under The Workers' Family Protection Act (29 U.S.C. 671a). U.S. Department of Health and Human Services (DHHS), National Institute for Occupational Safety and Health (NIOSH), (September 1995). Summarizes the hazards to which a worker's family may be exposed. UNITED STATES DEPARTMENT OF LABOR Occupational Safety and Health Administration 200 Constitution Ave NW Washington, DC 20210 ' 800-321-6742 (OSHA) TTY www.OSHA.gov FEDERAL GOVERNMENT White House Severe Storm and Flood Recovery Assistance Disaster Recovery Assistance DisasterAssistance.gov USA.gov No Fear Act Data U.S. Office of Special Counsel OCCUPATIONAL SAFETY AND HEALTH Frequently Asked Questions A - Z Index Freedom of Information Act Read the OSHA Newsletter Subscribe to the OSHA Newsletter OSHA Publications Office of Inspector General ABOUT THE SITE Freedom of Information Act Privacy & Security Statement Disclaimers Important Website Notices Plug-Ins Used by DOL Accessibility Statement https://www.osha.gov/SLTC/respiratoryprotection/index.html https://www.osha.gov/dsg/annotated-pels/index.html https://www.osha.gov/dsg/hazcom/index2.html https://www.osha.gov/Publications/OSHA3695.pdf https://www.osha.gov/SLTC/processsafetymanagement/index.html https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.119 https://www.osha.gov/SLTC/samplinganalysis/index.html https://www.cdc.gov/niosh/topics/chemical-safety/default.html https://www.cdc.gov/niosh/ncpc/ https://www.cdc.gov/niosh/docs/90-109/ https://www.cdc.gov/niosh/docs/95-123/ tel:800-321-6742 https://www.dol.gov/general/contact-phone-call-center%23tty https://www.osha.gov/ https://www.whitehouse.gov/ https://www.dol.gov/general/stormrecovery https://www.dol.gov/general/disasterrecovery https://www.disasterassistance.gov/ https://www.usa.gov/ https://www.dol.gov/agencies/oasam/civil-rights-center/resports/notification-and-federal-employee-antidiscrimination-retaliation-act-of-2002 https://osc.gov/ https://www.osha.gov/faq https://www.osha.gov/a-z https://www.osha.gov/foia https://www.osha.gov/quicktakes https://www.osha.gov/quicktakes/%23subscribe https://www.osha.gov/pls/publications/publication.html https://www.oig.dol.gov/ https://www.dol.gov/general/foia https://www.dol.gov/general/privacynotice https://www.dol.gov/general/disclaim https://www.dol.gov/general/aboutdol/website-policies https://www.dol.gov/general/aboutdol/file-formats https://www.dol.gov/general/aboutdol/accessibility

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