Respiratory Protection

Scope and Application

(Who Has to Use Respirators)

The OSHA respirator standard applies to all occupational airborne exposures to contaminated air where the employee is:

• Exposed to a hazardous level of an airborne contaminant; or
• Required by the employer to wear respirators; or
• Permitted to wear respirators.

Four major duties are imposed by each of these standards. These duties are:

• Use engineering controls where feasible to control the hazard;
• Provide an appropriate respirator;
• Ensure the use of an appropriate respirator; and
• Institute a respiratory protection program that complies with the rest of the standard.

References

• 29 CFR 1910 Subpart I, Personal protective equipment. OSHA Standard.
• 1910.134, Respiratory protection
• 1910.134(a), Permissible practice

Respiratory Protection Frequently Asked Questions

Q: What is a respirator?

A: A respirator is a protective facepiece, hood or helmet that is designed to protect the wearer against a variety of harmful airborne agents.

Q: When is the use of respirators required?

A: OSHA's respirator standard, 29 CFR 1910.134, requires the use of respirators to protect employees from breathing contaminated and/or oxygen-deficient air when effective engineering controls are not feasible, or while they are being instituted. Several other OSHA regulations also require the use of respirators.

Q: Can any respirator be used?

A: No, respirators shall be selected on the basis of hazards to which the worker is exposed (i.e., particulates, vapors, oxygen-deficiency, or combination). Also, OSHA requires the use of certified respirators.

Q: Who certifies respirators?

A: The National Institute for Occupational Safety and Health (NIOSH).

Q: How can a certified respirator be recognized?

A: On July 10, 1995, 30 CFR Part 11 certification procedures were replaced by 42 CFR Part 84 procedures. Under the 30 CFR Part 11 approval system, manufacturers were required to mark cartridges and filters with an abbreviated label that included a NIOSH/MSHA approval number ("TC number"). Under the 40 CFR Part 84 approval system, cartridges and filters are no longer marked with a "TC number". Instead, they are marked with "NIOSH", the manufacturer's name and part number, and an abbreviation to indicate the cartridge (e.g., OV, CL) or filter (e.g., N95, P100) type.

All cartridges and filters are to be supplied with a matrix approval label, usually as an insert in the box. This label shows the NIOSH approved configurations and includes the "TC number", component parts, and cautions and use limitations.

Nonpowered particulate respirators that were approved under 30 CFR Part 11 and use the "old" labeling were allowed to be manufactured and sold until July 10, 1998. Distributors were able to sell them and end-users were able to use them until their inventories were depleted.

NIOSH established the 42 CFR Part 84 test criteria to simulate worst-case respirator use. NIOSH encourages users to discontinue the use of particulate respirators certified under 30 CFR Part 11 and switch to particulate respirators certified under 42 CFR Part 84.

Samples of approval labels are shown on the following two pages.

PART 84 MATRIX APPROVAL LABEL

FPR P100 FILTER

DEF MANUFACTURING COMPANY ANYWHERE, USA 1-800-555-1234

2. CAUTIONS AND LIMITATIONS

• A- Not for use in atmospheres containing less than 19.5% oxygen.
• B- Not for use in atmospheres immediately dangerous to life or health.
• C- Do not exceed maximum use concentrations established by regulatory standards.
• J- Failure to use and maintain this product properly could result in injury or death.
• M- All approved respirators shall be selected, fitted, used and maintained in accordance with MSHA, OSHA, and other applicable regulations.
• N- Never substitute, modify, and, or omit parts. Use only exact replacement parts in the configuration specified by the manufacturer.
• O- Refer to user instruction and/or maintenance manuals for information about use and maintenance of these respirators.

Q: Which class of Part 84 respirator should be used where a particular OSHA standard requires the use of a respirator with HEPA filtration?

A: Where workers are exposed to a hazard that would require the use of a respirator with HEPA filtration, the appropriate class of respirator under the 42 CFR Part 84 certification is the Type 100 (N100, R100, or P100).

Q: Why is a formal respirator program needed?

A: A respirator program increases the chances of using a respirator correctly. A respirator will only protect if it is used correctly. Also, OSHA requires a number of written elements for all respiratory protection programs.

Q: Who is in charge of the respirator program?

A: The program must be administered by a trained program administrator who is qualified and knowledgeable in respiratory protection to run all aspects of the program.

Q: What do employees need to know about the respirator program?

A: Employers must establish and implement a written respiratory protection program with worksite-specific procedures and elements for required respirator use. The provisions of the program include procedures for selection, medical evaluation, fit testing, training, use and care of respirators.

Q: How is the proper respirator size determined?

A: Proper respirator size is determined through a fit test. Employees using negative or positive pressure tight-fitting facepiece respirators must pass an appropriate fit test using the procedures detailed in OSHA's respirator standard.

Q: Can employees check the fit of their own respirator?

A: Yes, employees using tight-fitting facepiece respirators are required to perform a user seal check each time they put on the respirator. They must use the procedures in Appendix B-1 of 29 CFR 1910.134 or procedures recommended by the respirator manufacturer that the employer demonstrates are as effective as OSHA's procedures. Note that a fit test is a method used to select the right size respirator for the user. A user seal check is a method to verify that the user has correctly put on the respirator and adjusted it to fit properly, as illustrated below.

Q: When is respirator fit testing required?

A: Fit testing of all negative or positive pressure tight-fitting facepiece respirators is required prior to initial use, whenever a different respirator facepiece is used, and at least annually thereafter. An additional fit test is required whenever there are changes in the user's physical condition that could affect respirator fit (e.g., facial scarring, dental changes, cosmetic surgery, or an obvious change in body weight). The employer must be fit tested with the same make, model, style, and size of respirator that will be used.

Q: What can be done if an employee has a very small face and has trouble being fit tested for a respirator?

A: Manufacturers make several different sizes. Respirators may also vary in size from manufacturer to manufacturer. Users may be able to get a better fit by trying a respirator made by another manufacturer. In some cases, the use of powered air-purifying respirators may be appropriate. Employers must help employees find a suitable respirator.

Q: Must employees see a doctor before they use a respirator?

A: The employer must provide a medical evaluation to determine the employee's ability to use a respirator before the employee is fit tested or required to use the respirator in the workplace. Not all workers must be examined by a doctor. A physician or other licensed health care professional must perform the medical evaluation using the medical questionnaire contained in Appendix C of 29 CFR 1910.134 or an initial medical examination that obtains the same information.

Q: What maintenance and care is required for respirators?

A: The employer must provide for the cleaning and disinfecting, storage, inspection, and repair of respirators used by employees according to the procedures in 29 CFR 1910.134.

Q: Can a respirator be used by more than one person?

How often should it be cleaned and disinfected?

A: Disposable respirators cannot be disinfected, and are therefore assigned to only one person. Disposable respirators must be discarded if they are soiled, physically damaged, or reach the end of their service life. Replaceable filter respirators may be shared, but must be thoroughly cleaned and disinfected after each use before being worn by a different person, using the procedures in Appendix B-2 of 29 CFR 1910.134, or equally effective procedures recommended by the manufacturer.

Q: How long can a particulate respirator be used before it must be discarded?

A: Respirators with replaceable filters are reusable, and a respirator classified as disposable may be reused by the same worker as long as it functions properly. All filters must be replaced whenever they are damaged, soiled, or causing noticeably increased breathing resistance (e.g., causing discomfort to the wearer). Before each use, the outside of the filter material should be inspected. If the filter material is physically damaged or soiled, the filter should be changed (in the case of respirators with replaceable filters) or the respirator discarded (in the case of disposable respirators). Always follow the respirator filter manufacturer's service-time-limit recommendations.

Employers must develop standard operating procedures for storing, reusing, and disposing of respirators that have been designated as disposable and for disposing of replaceable filter elements.

Q: What is the proper way to store a respirator that is used routinely?

A: Respirators must be stored to protect them from damage, contamination, dust, sunlight, extreme temperatures, excessive moisture, and damaging chemicals. They must also be packed or stored to prevent deformation of the facepiece and exhalation valve. A good method is to place them in individual storage bins. Keep in mind that respirator facepieces will become distorted and the straps will lose their elasticity if hung on a peg for a long time. Check for these problems before each use.

Storing the respirator in a plastic sealable bag after use is not considered a good practice. The respirator may be damp after use and sealing prevents drying and encourages microbial growth. If plastic bags are used, respirators must be allowed to dry before storage.

Q: Are there any additional requirements for the storage of emergency respirators?

A: Yes, emergency respirators must be kept accessible to the work area and stored in compartments or in covers that are clearly marked as containing emergency respirators, and stored in accordance with any applicable manufacturer instructions.

Q: What are the employer's obligations when respiratory protection is not required but employees wear respirators on their own accord?

A: The employer must implement those elements of the written respiratory protection program necessary to ensure that any employee using a respirator voluntarily is medically able to use that respirator, and that the respirator is cleaned, stored, and maintained so its use does not present a health hazard to the user. Also, employers must provide the voluntary respirator users with the information contained in Appendix D of 29 CFR 1910.134.

Employers are not required to include in a written respiratory program those employees whose only use of respirators involves the voluntary use of filtering facepieces (dust masks

Q: Is training required before a respirator is used?

A: Yes, training must be provided to employees who are required to use respirators. The training must be comprehensive, understandable, and recur annually, and more often if necessary. This training should include at a minimum: Why the respirator is necessary and how improper fit, use, or maintenance can compromise its protective effect

• Limitations and capabilities of the respirator
• Effective use in emergency situations
• How to inspect, put on and remove, use and check the seals
• Maintenance and storage
• Recognition of medical signs and symptoms that may limit or prevent effective use
• General requirements of OSHA's respirator standard, 29 CFR 1910.134

Q: What can be done if employees find it difficult to talk with co-workers when wearing a respirator?

A: Some respirators may interfere with speech more than others. Devices that enhance speech communication are available. Ask your program administrator if there are alternatives.

Q: If employees have a beard or moustache, is their respirator still effective?

A: Tight-fitting facepiece respirators must not be worn by employees who have facial hair that comes between the sealing surface of the facepiece and the face or that interferes with valve function. Respirators that do not rely on a tight face seal, such as hoods or helmets, may be used by bearded individuals.

Q: Can employees wear glasses while wearing a respirator?

A: Yes, but if an employee wears corrective glasses or goggles or other personal protective equipment, the employer must ensure that such equipment is worn in a manner that does not interfere with the seal of the facepiece to the face of the user. Kits are available from all respirator manufacturers that allow the mounting of prescription lenses inside the respirator.

Contact lenses can be worn with any type of respirator, but their use is not recommended in dusty atmospheres while wearing a half-mask facepiece.

Q: If employees get a rash when they wear a respirator with a latex seal, how can this be prevented?

A: Users might have an allergy or sensitivity to the latex or its additives used in the manufacture of some respirators. Changing to a respirator using a silicone-based compound for the face seal, or a respirator that doesn't have a face seal (like a hooded PAPR) may solve the problem. Employers must help employees find a respirator that does not cause this problem.

Respirator Users

Almost all elements of the respiratory protection program affect respirator users and their knowledge of the principles of respiratory protection is integral to an effective program. Elements that have a more direct impact on the user include knowledge of selection criteria, medical evaluations, procedures for proper use, fit-testing, and maintenance procedures. Proper selection and, if appropriate, fit testing of tight fitting face pieces will assure that the respirator will provide adequate protection against the contaminants that affect use. Medical evaluations are necessary to determine whether the user is fit to wear a respirator without adverse health effects. Training on procedures for proper use and maintenance will assure the wearer that the wearer is using the respirator in a safe and healthful manner.

References

• 29 CFR 1910 Subpart I, Personal protective equipment. OSHA Standard.

• 1910.134, Respiratory protection

• 1910.134(d), Selection of respirators
• 1910.134(e), Medical evaluation
• 1910.134(f), Fit-testing
• 1910.134(g), Use of respirators
• 1910.134(h), Maintenance and care of respirators
• 1910.134(i), Breathing air quality and use
• 1910.134(k),Training and information
• Appendix B-1, User seal check procedures (Mandatory)

Medical Requirements

Employees need to be medically cleared to wear respirators before commencing use. All respirators generally place a burden on the employee. Negative pressure respirators restrict breathing, some respirators can cause claustrophobia and self-contained breathing apparatuses are heavy. Each of these conditions may adversely affect the health of some employees who wear respirators. A physician or other licensed health care professional operating within the scope of his/her practice needs to medically evaluate employees to determine under what conditions they can safely wear respirators.

References

• 29 CFR 1910 Subpart I, Personal protective equipment. OSHA Standard.

• 1910.134, Respiratory protection

• 1910.134(e), Medical evaluation
• Appendix C, OSHA respirator medical evaluation questionnaire (Mandatory)

Maintenance and Care of Respirators

The proper functioning of respirators and ensuring that the devices themselves do not pose a hazard to the user require a regular maintenance and cleaning schedule. In general, respirators should be inspected for basic function prior to each use and cleaned as often as necessary to prevent the occurrence of unsanitary conditions.

References

• 29 CFR 1910 Subpart I, Personal protective equipment. OSHA Standard.

• 1910.134, Respiratory protection

• 1910.134(h), Maintenance and care of respirators
• Appendix B-2, Respirator cleaning procedures (Mandatory)

Fit Testing

All respirators that rely on a mask-to-face seal need to be annually checked with either qualitative or quantitative methods to determine whether the mask provides an acceptable fit to a wearer. The qualitative fit test procedures rely on a subjective sensation (taste, irritation, smell) of the respirator wearer to a particular test agent while the quantitative use measuring instruments to measure face seal leakage. The relative workplace exposure level determines what constitutes an acceptable fit and which fit test procedure is required. For negative pressure air purifying respirators, users may rely on either a qualitative or a quantitative fit test procedure for exposure levels less than 10 times the occupational exposure limit. Exposure levels greater than 10 times the occupational exposure limit must utilize a quantitative fit test procedure for these respirators. Fit testing of tight-fitting atmosphere-supplying respirators and tight-fitting powered air-purifying respirators shall be accomplished by performing quantitative or qualitative fit testing in the negative pressure mode.

References

• 29 CFR 1910 Subpart I, Personal protective equipment. OSHA Standard.

• 1910.134, Respiratory protection

• 1910.134(f), Fit testing
• Appendix A, Fit testing procedures (Mandatory)

Written Program

The requirement for a respirator program to be in writing entails a great deal of pre-planning of the implementation steps for the program. These steps include selection, medical fitness, maintenance, training, fit testing, use, program evaluation, etc. This pre-planning is by design and intended to ensure the respirator wearer is safely using the proper respirator. The program evaluation facet allows for continuous improvements or changes to be made, as necessary, to maintain a protective program.

References

• 29 CFR 1910 Subpart I, Personal protective equipment. OSHA Standard.

• 1910.134, Respiratory protection

• 1910.134(c), Respiratory protection program
• 1910.134(l), Program evaluation
• 1910.134(m), Recordkeeping

Employee Voluntary Use of Respirators

Employers who allow their employees to wear respirators on a voluntary basis when not required by OSHA or the employer must implement limited provisions of a respiratory protection program. When a filtering face piece respirator is all that is used, the employee must be provided a copy of Appendix D. For all other voluntary users, an additional written respirator program that covers medical fitness and proper maintenance procedures must be implemented.

References

• 29 CFR 1910 Subpart I, Personal protective equipment. OSHA Standard.

• 1910.134, Respiratory protection

• 1910.134(c)(2), Where respirator use is not required
• Appendix D, (Mandatory) Information for employees using respirators when not required under standard

Respirator Change Schedules

Respirator cartridges don't last forever!

A change schedule is the part of the written respirator program which says how often cartridges should be replaced and what information was relied upon to make this judgment. A cartridge's useful service life is how long it provides adequate protection from harmful chemicals in the air. The service life of a cartridge depends upon many factors, including environmental conditions, breathing rate, cartridge filtering capacity, and the amount of contaminants in the air. It is suggested that employers apply a safety factor to the service life estimate to assure that the change schedule is a conservative estimate.

If you know what the chemical is and how much of it you are exposed to, then you are ready to estimate out how long your respirator cartridges will work and apply the safety factor.

3 valid ways for you to estimate a cartridge's service life

1. Conduct Experimental Tests

• Can save money by providing a more accurate service life value instead of relying on conservative assumptions made by other methods
• Most reliable method, especially for multiple contaminants
• Can be used to validate an existing change schedule
• Will likely take time and money to perform the tests

2. Use the Manufacturer's Recommendation

• Can result in a more accurate estimate for your particular brand of respirator
• Relies on the manufacturer's broad knowledge and expertise
• May not be possible if the manufacturer is unable to provide a recommendation
• May not account for all workplace and user factors adequately

3. Use a Math Model

• Inexpensive and takes little time
• Requires no math calculations if you use the Advisor Genius
• Not as accurate as experimental testing. May result in a service life estimate that is shorter than it needs to be due to conservative assumptions
• Generally limited to single contaminant situations

Keep In Mind

• You may not rely on odor thresholds and other warning properties as the primary basis for determining the service life of gas and vapor cartridges and canisters.
• You should account for environmental and user factors and use a conservative approach when evaluating service life testing data.
• You should apply a safety factor to any estimate to account for uncertainty.
• Mixtures, intermittent use and concentrations, storage practices and other variables may require the use of an administrative time limit, e.g. one day, even though the estimated life would be longer.
• An example of a decision logic tree which could be used when evaluating a workplace for use of air purifying respirators is presented in these pages.
• There is a published "Rule of Thumb" that may provide a rough estimation of cartridge service life. However, you should NOT use this as the sole method of determining service life.

OSHA Requirements for Change Schedules

The following is a synopsis of the some of the requirements of the standard.

• Employers develop cartridge/canister change schedules based on available data or information. Such information includes the exposure assessment and information based on breakthrough test data, mathematically based estimates, and/or reliable use recommendations from the employer's respirator and/or chemical suppliers.
• Reliance on odor thresholds and other warning properties will not be permitted as the primary basis for determining the service life of gas and vapor cartridges and canisters.
• OSHA emphasizes that a conservative approach is recommended when evaluating service life testing data. Temperature, humidity, air flow through the filter, the work rate, and the presence of other potential interfering chemicals in the workplace all can have a serious effect on the service life of an air-purifying cartridge or canister.

The standard requirements for change schedules are found in:

• 29 CFR 1910.134(d)(3)(iii)(B)(2)

For enforcement policy and guidance, see the OSHA Directive for Inspection procedures for the Respiratory Protection Standard.

For additional background material, see the OSHA Preamble to Final Rules for Respiratory Protection.

Factors that can Reduce Cartridge Service Life

Worker Exertion Level: a worker breathing twice as fast as another will draw twice the amount of contaminant through the respirator cartridge

The service life of a cartridge or canister respirator depends upon the total amount of contaminant captured by the absorbent. The total amount of captured contaminant is directly related to the work rate or breathing rate; i.e., a worker breathing twice as fast as another will draw twice the amount of contaminant through the respirator cartridge. Most cartridge studies have used a breathing rate, 50-60 liters per minute, that approximates a high end of moderate work rate. For work rates that exceed this level (e.g., heavy shoveling, running) you may need to apply or take into account a correction factor when determining a service life.

Respirator Cartridge Variability: some cartridges contain more activated charcoal than others

The service life of a respirator cartridge is directly related to the amount of active material in the cartridge. For instance, most dual cartridge organic vapor respirators contain between 35-50 grams of activated charcoal in each cartridge. If the specific cartridge being evaluated can be reproducibly determined to have a certain amount of active material, then modifications to the service life may be justified. You can obtain information on cartridge specifications from manufacturers.

Temperature: the hotter it is, the shorter the service life

High temperatures can adversely affect the adsorptive capacity of respirator cartridges and canisters. The high temperature may act by thermally loosening the attractive forces that make adsorption happen or may act in concert with humidity by increasing the moisture carrying capacity of air. This latter mechanism may represent the greatest likely effect on service lives of cartridges. Temperature effects alone have been reported to reduce the service life 1-10% for every 10 degrees Celsius rise depending on the specific solvent (Nelson, et. al., 1976). Corrections to cartridge estimated service life for this effect alone are probably not necessary under normal working temperatures.

Relative Humidity: water vapor will compete with the organic vapors for active sites on the adsorbent

Relative Humidity is a measure of the amount of water vapor the air will hold at a specified temperature and is expressed in percentage values. Since warmer air will hold more water than colder air, the same relative humidity at a higher temperature represents a significantly greater amount of moisture. High relative humidity is a significant negative factor in the capacity of organic vapor cartridges since the large quantity of water vapor will compete with the organic vapors for active sites on the adsorbent. Most of the laboratory work determining adsorbent capacity has been performed at a low relative humidity of 50% at approximately 70 degrees F.

If the actual use of the organic vapor respirators will take place in a significantly more humid environment, then you may need to apply or take into account a safety factor when determining a service life. The exact magnitude of the humidity effect is complex, dependent in part upon chemical characteristics and concentrations of both the contaminant and the water vapor. Based upon relatively few studies, a reduction by a factor of 2 in the cartridge service life originally estimated based upon 50 % relative humidity, may be made when the relative humidity reaches 65% (Nelson, et. al., 1976; Werner, 1985). If the relative humidity exceeds 85%, you should consider experimental testing or another method to more specifically determine the service life. Mathematical modeling may be an appropriate, albeit complex, approach to predict the effect of humidity at various chemical concentrations (Wood, 1987; Underhill, 1987).

Multiple Contaminants: predictions should be derived from the least well adsorbed compound

Multiple contaminants introduce a great deal of variability into the prediction of service life for respirator cartridges. Much of the laboratory testing and the mathematical models have utilized a single contaminant to determine service lives. Only a limited number of multiple contaminant situations have been studied and reported in the literature (e.g. Yoon, 1996; Jonas et. al., 1986). Cartridge service life for mixtures of compounds with significantly different chemical characteristics is probably best determined by experimental methods. Predictions based upon models without experimental data should probably be very conservative and ascribe the service life derived from the least well adsorbed compound to the total mixture concentration in terms of parts per million. The displacement of a less well adsorbed compound by a more highly adsorbed one may alter the actual service life from the estimated one in some cases.

Conducting Experimental Tests to Determine a Cartridge's Service Life

Keep In Mind

• There is no widely accepted, standard protocol for performing service life testing.
• OSHA has devised a field testing approach which will demonstrate the validity of an established change schedule.
• A field testing approach is provided by Cohen, H. J., Development of a Field Method for Calculating the Service Lives of Organic Vapor Cartridges – Part IV. Results of Field Validation Trials, American Industrial Hygiene Association Journal, (1991), pages 263-270.
• Ideally, respirator cartridges should be tested under worst case conditions either in the workplace or in the laboratory.
• The determination of breakthrough from workplace testing does not require the determination of the full breakthrough curve for the respirator cartridge.

Using the Manufacturer's Recommendation to Determine a Cartridge's Service Life

Chemical and respirator manufacturers may be able to provide an estimate based upon their own expertise and testing data.

Keep In Mind

• Manufacturers are likely to possess the most accurate data for their own respiratory products.
• However, the manufacturer may not have tested the respirator with the chemicals that you work with, and therefore may not be able to offer a reliable recommendation.

Using a Math Model Table to Determine a Cartridge's Service Life

Mathematical equations have been used to predict the service lives of organic vapor respirator cartridges when used for protection against single contaminants. Using an equation developed by G. Wood, OSHA has precalculated and presented some service lives in a table. You can calculate others using the Advisor Genius. It is suggested that you reduce the service life estimate by some safety factor to give a change schedule that you should document in your written respiratory program.

Example: Using Math Model Table Example: Using a Math Model Equation

Using a Math Model Table

Using a Math Model Equation

Keep In Mind

• The math models are usually only directly applicable for single contaminant exposures. If you have a multiple contaminant situation, you may need to use other methods to derive a schedule or increase the safety factors.
• The Wood Math Model is just one equation you can use. Also, because it is a predictive type of model (as opposed to a descriptive type), you should not rely on it without some experimental confirmation of the calculation or use of appropriate safety factors.
• The Yoon-Nelson Mathematical Model is an example of a descriptive math model.

Respirator Selection

In order to select an appropriate respirator you must:

• Conduct an exposure assessment to determine the type and amount of hazardous exposure
• Take into account the factors that can influence respirator selection such as job-site and worker characteristics
• Understand the assigned protection factors
• Know the various kinds of respirators and their relevant characteristics

Factors That Can Influence Respirator Selection

The Physical Configuration of the Jobsite

Tightly constrained areas may not permit the use of self-contained breathing apparatuses even though they might be an acceptable choice otherwise. Likewise, working around obstructions or moving machinery that can snag hoses may limit the use of airline respirators.

Worker Medical Condition

Wearing respiratory protection poses a physical burden on the wearer. When a worker's medical condition would prohibit restrictive breathing conditions, negative pressure respirators would not be an appropriate choice.

Worker Comfort

Worker preferences should be a consideration during the respirator selection process. Among air purifying respirators, powered air purifying helmets have been subjectively rated the best for breathing ease, skin comfort, and in-mask temperature and humidity while filtering facepieces rated high for lightness and convenience. Each, however, has its own drawbacks, and all these factors should be taken into account during selection.

Assigned Protection Factors

The assigned protection factor (APF) of a respirator reflects the level of protection that a properly functioning respirator would be expected to provide to a population of properly fitted and trained users. For example, an APF of 10 for a respirator means that a user could expect to inhale no more than one tenth of the airborne contaminant present.

See Table 1. -- Assigned Protection Factors, 29 CFR 1910.134(d)(3)(i)(A).

Keep In Mind

• Various groups such as the National Institute for Occupational Safety and Health (NIOSH), the Occupational Safety and Health Administration (OSHA), and the American National Standards Institute (ANSI) have proposed factors for the different types of respirators available.
• OSHA will enforce the APFs listed in its standards unless an alternative APF has been granted by a specific OSHA interpretation.

Three Kinds of Air-purifying Respirators

Particulate Respirators

• capture particles in the air, such as dusts, mists, and fumes
• do not protect against gases or vapors
• generally become more effective as particles accumulate on the filter and plug spaces between the fibers
• filters should be replaced when user finds it difficult to breath through them

Combination Respirators

• are normally used in atmospheres that contain hazards of both particulates and gases
• have both particulate filters and gas/vapor filters
• may be heavier

Gas & Vapor Respirators

• are normally used when there are only hazardous gases and vapors in the air
• use chemical filters (called cartridges or canisters) to remove dangerous gases or vapors
• do not protect against airborne particles
• are made to protect against specific gases or vapors
• provide protection only as long as the filter's absorbing capacity is not depleted
• the service life of the filter depends upon many factors and can be estimated in various ways

(see Selection Criteria for Particulate Filters)

Three Kinds of Atmosphere-supplying Respirators

Air-Supplied Respirators

• makes use of a hose to deliver clean, safe air from a stationary source of compressed air
• provides clean air for long periods of time and are light weight for the user
• limits the range of user-mobility and may fail due to hose damage
• also called airline respirators
• are normally used when there are extended work periods required in atmospheres that are not immediately dangerous to life and health (IDLH)

Combination Respirators

• have an auxiliary self-contained air supply that can be used if the primary supply fails
• the self-contained portion can be small since it only needs to supply enough air for escape
• can be used for entry into confined spaces
• are normally used when there are extended work periods required in atmospheres that are or may be immediately dangerous to life and health (IDLH)

Self-Contained Breathing Apparatus

• consists of a wearable, clean-air supply pack
• do not restrict movement with a hose connection
• the closed-circuit type can provide air up to 4 hours
• the open-circuit type only provide air for 30 - 60 minutes
• are normally used when there is a short-time need to enter and escape from atmospheres which are or may be immediately dangerous to life and health (IDLH)

• Employers are required to provide employees using atmosphere-supplying respirators (supplied air and self contained breathing apparatus) with breathing gases of high purity, and shall ensure that compressed air, compressed oxygen, liquid air, and liquid oxygen used for respiration is in accordance with the specifications of OSHA Standard 29 CFR 1910.134(i).