Introduction		Respiratory Protection Factors
	Respirator Types		Selection of Respirators for Routine Use
	Selection Criteria		Additional Considerations
	Hazard Determination		IDLH Atmospheres

Introduction
Choosing the right respirator involves several steps including (1) determining what the hazard is and its extent, (2) choosing equipment that is certified for the function and (3) assuring that the device can perform the intended function.

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Respirator Types
Respirators fall into three general classes: (1) air purifying, (2) atmosphere or air supplied, and (3) combination air-purifying and atmosphere-supplying. The type of respirator selected depends on the nature of the contaminant (e.g., dust vs. vapor), and the conditions under which it will be used (e.g., fire or rescue).

Air-purifying respirators

Air-purifying respirators use filters or sorbents to remove harmful substances from the air. They range from simple, disposable masks to sophisticated powered air-purifying respirators. Air-purifying respirators do not supply oxygen and may not be used in oxygen-deficient atmospheres or in atmospheres that are immediately dangerous to life or health (IDLH).

Under the most recent NIOSH certification rules, particulate filter respirators are further classified as N (Not resistant to oil), R (Resistant to oil) and P (oil Proof). Each category of filter has three levels of filter efficiency (95 percent, 99 percent and 99.97 percent).

Atmosphere-supplying respirators
Atmosphere-supplying respirators are designed to provide breathable air from a clean air source other than the surrounding contaminated work atmosphere. They range from supplied-air respirators and self-contained breathing apparatus (SCBAs) to complete air-supplied suits.

Combination
Combination air-purifying and atmosphere-supplying respirators are a combination of an air-line respirator and an auxiliary air-purifying attachment, which provides protection in the event the air supply fails. The most popular versions are ones in which the air-purifying element is a HEPA filter, but devices are available with complete arrays of chemical cartridges as well. These respirators do have limitations:

• They are not for use in IDLH atmospheres.
• They are not for use in atmospheres containing less than 19.5 percent oxygen.
• Use only the hose lengths and pressure ranges specified on the approval label.
• Use only in atmospheres for which the air-purifying element is approved.

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Selection Criteria
The proper selection, maintenance and use of respirators can prevent serious injury and death. Selecting the appropriate respirator requires an evaluation of various factors. These include:

Airborne contaminant:

The specific airborne contaminant(s) to which workers are exposed and the airborne concentrations measured, or expected, in the work area. The presence of oil in the aerosol is critical when selecting particulate respirators.

Worker activity and location:

Is the employee in the hazardous area continuously or intermittently during the work shift? Is the work rate light, medium or heavy?

Respirator use conditions:

The period of time that a respirator must be worn is an important factor that should be taken into account when selecting a respirator. Consideration should be given to the type of respirator application, (e.g., routine, nonroutine, emergency or rescue use).

Location of the potential hazardous area:

The location of the hazardous area with respect to a safe area having respirable air should be considered. This will permit planning for the escape of workers if an emergency occurs, for the entry of workers to perform maintenance duties and for rescue operations.

Respirator characteristics, capabilities, and limitations:

The physical characteristics, functional capabilities and the performance limitations of the various types should be considered.

Operational limitations:

Environmental conditions and the level of effort required of the respirator wearer may affect service life. For example, extreme physical exertion can cause the user to deplete the air supply in a SCBA (Self-Contained Breathing Apparatus) such that service life is reduced by half or more.

When selecting any respirator, only NIOSH-approved or certified respirators should be selected. Any change or modification, however minor, may void the respirator approval and significantly affect its performance.

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Hazard Determination
Prior to selecting and issuing a respirator, a determination of the nature of the chemical hazard must be made. This information is critical in ensuring that the proper type of respirator is selected. The steps in hazard determination include:

• Determine what contaminant(s) may be present in the workplace. This information can be obtained by reviewing the Material Safety Data Sheets (MSDSs).
  
  
• Determine whether there is a published Threshold Limit Value (TLV), Permissible Exposure Limit (PEL) or any other available exposure limit or estimate of toxicity for the contaminant(s). Determine if the IDLH (Immediately Dangerous to Life and Health) concentration for the contaminant is available.
  
  
• Determine if there is an OSHA substance-specific standard (e.g., lead, formaldehyde, asbestos) for the contaminant(s). If so, there may be specific respirators required that will influence the selection process.
  
  
• If the potential for an oxygen-deficient environment exists, measure the oxygen content.
  
  
• Measure the concentration of the contaminant(s).
  
  
• Determine the physical state of the contaminant (gas, vapor or aerosol). If an aerosol (liquid or solid particles), determine or estimate the particle size. Determine if vapor pressure of the aerosol is significant at the maximum expected temperature of the work environment.
  
  
• Determine whether the contaminant(s) present can be absorbed through the skin, produce skin sensitization or be irritating or corrosive to the eyes and skin.
  
  
• Determine for a gas or vapor contaminant(s) if a known odor, taste or irritation threshold concentration exists.

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Respirator Protection Factors
The protection factor of a respirator is an expression of performance based on the ratio of two measured variables, Ci and Co. The variable Ci is defined as the measured concentration of a contaminant inside the respirator facepiece cavity, and Co is the measured contaminant concentration outside the respirator facepiece. For any particular respirator/person combination, it is important to recognize that the measured variable Ci becomes a complicated function of many individual sources of penetration or leakage (e.g., air-purifying element penetration, exhalation valve penetration, face seal penetration) and those environmental conditions that would affect penetration.

A special application of the general protection factor concept is the Assigned Protection Factor (APF). APF is defined as a measure of the minimum anticipated workplace level of respiratory protection that would be provided by a properly functioning respirator or class of respirators to a percentage of properly fitted and trained users.

Assigned Protection Factors have been determined empirically in laboratory settings. There are two major sources of APFs:

• The American National Standards Institute Z88.2-1992 Practices for Respiratory Protection
  
  
• The NIOSH Respirator Decision Logic, published in 1987.

While there is some agreement between these two sources, there are also some significant differences in APFs for certain respirators, especially for full-facepiece respirators.

The paragraphs in the OSHA standard on APFs and MUCs (defined below) were left "reserved" when the revised standard was published on 01/08/1998. In August of 2006, OSHA re-published the Respirator Protection Standard 1910.134 to include Assigned Protection Factors. This kit, therefore includes the NIOSH APFs in Figure 1 of this section, and the OSHA APFs in the OSHA Standard section.

A related measure of respirator protection is the Maximum Use Concentration. The MUC is generally determined by multiplying the exposure limit for the contaminant by the protection factor assigned to a specific class of respirators.

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Selection of Respirators for Routine Use
The following selection steps are adapted from the American National Standard for Respiratory Protection (ANSI Z88.2-1992) and the OSHA Respiratory Protection Standard.

The selection steps are also presented as a Flowchart in Figure 2.

1. If unable to determine what potentially hazardous contaminant may be present, the atmosphere should be considered IDLH. Refer to the respirator selection guidelines for atmospheres immediately dangerous to life and health.
   
   
2. If no exposure limit or guideline is available, and estimates of the toxicity cannot be made, the atmosphere should be considered IDLH. Refer to the respirator selection guidelines for atmospheres immediately dangerous to life and health.
   
   
3. If the measured or estimated concentration of the contaminant(s) is considered IDLH, refer to the respirator selection guidelines for atmospheres immediately dangerous to life and health.
   
   
4. If a specific OSHA standard exists for the contaminant, follow those guidelines/ requirements (e.g., lead, asbestos, formaldehyde).
   
   
5. If there is an oxygen-deficient atmosphere, the type of respirator selected depends on the partial pressure and concentration of oxygen and the concentration of the other contaminant(s) that may be present. Refer to the respirator selection guidelines for reduced-pressure atmospheres.
   
   
6. Divide the measured or estimated concentration of each contaminant by the exposure limit or guidelines to obtain a hazard ratio (HR). When two or more substances are present, consideration needs to be given if there is a synergistic or combined effect of exposure rather than considering each substance individually. Select a respirator with an assigned protection factor (APF) greater than the value of the hazard ratio by using Figure 1.

   Example: An employee is exposed to Toluene vapors at an average concentration of 200 ppm. The ACGIH TLV for Toluene is 50 ppm. The hazard ratio = 4. The minimum respirator selected must be a half-mask air-purifying respirator, equipped with the appropriate cartridge (APF=10).

7. If the contaminant(s) is a gas or vapor only, select a device with an assigned protection factor that is greater than the hazard ratio. The concentration should also be less than the maximum use concentration of the cartridge/canister.
   
   
8. If the contaminant is a paint, lacquer, enamel or pesticide, select a combination respirator consisting of an organic vapor cartridge and a particulate filter (based on the presence of oil aerosols) or an atmosphere-supplying respirator.
   
   
9. If the contaminant is an aerosol (particulate) with an unknown particle size, or if it is known to be less than 2 µm (mass medium aerodynamic diameter [MMAD]), a high-efficiency filter (or N100, R100, P100 filter) should be used.
   
   
10. If the contaminant is a gas or vapor and has poor warning properties (meaning that a hazardous concentration does not trigger a sensation of smell or irritation), the use of an atmosphere-supplying respirator is generally recommended. When atmosphere-supplying respirators cannot be used because of the lack of a feasible air supply or because of the need for worker mobility, air-purifying devices should be used only if:
    
    
    • The air-purifying respirator has a reliable end-of-service-life indicator that will warn the user prior to contaminant breakthrough or,
      
      
    • A cartridge change schedule is implemented based on cartridge service data including desorption studies (unless cartridges are changed daily), expected concentration, pattern of use and duration of exposure have been established, and the chemical does not have a ceiling limit.

The hazard evaluation and respirator selection process should be documented for each job or task where respirators are provided or required. The Hazard Evaluation and Respirator Selection Record can be used for this purpose.

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Additional Considerations
The following factors should be considered when providing the selected respirators to employees.

Facial hair:

A respirator, either positive or negative pressure, equipped with a facepiece (tight or loose-fitting) should not be worn if facial hair comes between the sealing surface of the facepiece and the face, or if facial hair interferes with valve function.

Communications:

Verbal communications in a noisy industrial environment can be difficult. It is important to ensure that respirator wearers can comfortably communicate when necessary, because a worker who is speaking loudly or yelling may cause a facepiece seal leak, and the worker may be tempted to temporarily dislodge the device to communicate. Several options that may be employed to aid communication between employees include:

• speaking diaphragms
• built-in microphones
• hand or coded signals
• cranial, throat or ear microphones.

Vision:

When a respirator user must wear corrective lenses, a protective spectacle or goggle, a face shield, a welding helmet or other eye- and face-protective devices, the item shall be fitted to provide good vision and be worn in such a manner as not to interfere with the seal of the respirator.

Respirator-sealing problems:

A head covering that passes between the sealing surface of a tight-fitting respirator facepiece and the wearer's face should not be used. The head harness straps of tight-fitting respirators should not be positioned or worn over hard hats. Wearing a hard hat or other protective equipment may not be allowed to interfere with the seal of the respirator.

Respirator use in low-temperature environments:

Low temperatures may cause detrimental effects on the performance of respirators (e.g., fogging of the lens in a respiratory inlet covering and freezing or improper sealing of the valves). The effects of low temperatures should be considered in the selection and maintenance of respirators and respirable gas supplies.

Respirator use in high-temperature environments:

High temperatures may affect the performance of the respirator and may add undue physiological stress. The effects of high temperatures should be considered in respirator selection and for medical approvals.

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Atmospheres Immediately Dangerous to Life or Health (IDLH)
A location is considered IDLH when:

• it is an atmosphere known or suspected to have chemical concentrations above the IDLH level; or,
  
  
• it is a confined space that contains less than the normal 20.9 percent oxygen, unless the source of the oxygen reduction is understood and controlled; or,
  
  
• oxygen content is below 12.5 percent (95 mmHg ppO2) at sea-level atmospheric pressure; or,
  
  
• it contains total atmospheric pressure less than 450 mmHg (8.6 psi) equivalent to 14,000 ft
  (4270 m) altitude or any combination or reduced percentage of oxygen or reduced pressure that leads to an oxygen partial pressure less than 95 mmHg.

Note: OSHA standard 1910.134 requires that . . . "All oxygen-deficient atmospheres (i.e., those below 19.5 percent O2 be considered IDLH. Exception: If the employer demonstrates that, under all foreseeable conditions, the oxygen concentration can be maintained within the ranges specified in Table II of this section (i.e., for the altitudes set out in the table), then any atmosphere-supplying respirator may be used."

Respirators for use under IDLH conditions at normal atmospheric pressure

OSHA standard 1910.134 requires employers to provide the following respirators for employee use in IDLH atmospheres:

• A full-facepiece pressure-demand SCBA certified by NIOSH for a minimum service life of 30 minutes.
  
  
• A combination full facepiece pressure-demand supplied-air respirator (SAR) with auxiliary self-contained air supply.
  

Respirators provided only for escape from IDLH atmospheres shall be NIOSH-certified for escape from the atmosphere in which they will be used. (See Figure 3).

• In addition to requiring only positive pressure, air-supplied respirators for all IDLH atmospheres, the OSHA standard also requires the employer to ensure that:
  
  
• One employee, or, when needed, more than one employee is located outside the IDLH atmosphere.
  
  
• Visual, voice, or signal line communication is maintained between the employee(s) in the IDLH atmosphere and the employee(s) located outside the IDLH atmosphere.
  
  
• The employee(s) located outside the IDLH atmosphere are trained and equipped to provide effective emergency rescue.
  
  
• The employer or designee is notified before the employee(s) located outside the IDLH atmosphere enter the IDLH atmosphere to provide emergency rescue.
  
  
• The employer or designee authorized to do so by the employer, once notified, provides necessary assistance appropriate to the situation.
  
  
• Employee(s) located outside the IDLH atmospheres are equipped with pressure-demand or other positive-pressure SCBAs, or a pressure-demand or other positive-pressure supplied-air respirator with auxiliary SCBA; and either
  
  
  • appropriate retrieval equipment for removing employee(s) who enter(s) these hazardous atmospheres where retrieval equipment would contribute to the rescue of the employee(s) and would not increase the overall risk resulting from entry; or
    
    
  • equivalent means for rescue where retrieval equipment is not required.
    

Respirators for use under reduced atmospheric pressure conditions
An oxygen partial pressure less than 95 mmHg (12.5 percent at sea level) is considered IDLH. An oxygen partial pressure of 95 to 122 mmHg is considered an oxygen-deficient atmosphere that is not immediately dangerous to life. Such an atmosphere may adversely affect a person with reduced tolerance to reduced oxygen levels or adversely affect the unacclimatized person performing work requiring a high degree of mental acuity or heavy stress. Under these conditions, a supplied air respirator is required.

Respirators for use during fire fighting
Only a self-contained breathing apparatus (SCBA) with a full facepiece operated in pressure demand or other positive-pressure mode is recommended.

In addition to the requirements listed for all IDLH atmospheres, OSHA 1910.134 requires the employer to ensure that:

• At least two employees enter the IDLH atmosphere and remain in visual or voice contact with one another at all times.
  
  
• At least two employees are located outside the IDLH atmosphere.
  
  
• All employees engaged in interior structural firefighting use SCBAs.
  

Respirators for use during escapes
Escape devices have a single function: to allow a person working in a normally safe environment sufficient time to escape from suddenly occurring respiratory hazards. When selecting escape apparatus, careful consideration must be given to potential eye irritation. This consideration is important for determining whether a gas mask or SCBA equipped with a full facepiece should be selected, rather than a device equipped with a half-mask or mouthpiece. Refer to Figure 3 for the selection options for escape respirators.

Air quality for supplied air respirators
Compressed air, compressed oxygen, liquid air and liquid oxygen used for respirators should be of high purity. Oxygen should meet the requirements of the United States Pharmacopoeia for medical or breathing oxygen. Breathing air must meet the requirements of the Compressed Gas Association Specification G-7.1-1989, Grade D air. This requires:

• Oxygen content of 19.5-23.5 percent
  
  
• Hydrocarbon content of 5 mg/m3 of air or less
  
  
• Carbon monoxide content of 10 ppm or less
  
  
• Carbon dioxide content of 1000 ppm or less
  
  
• Lack of noticeable odor
  

Compressed oxygen should not be used in supplied-air respirators or in open circuit self-contained breathing apparatus that have previously used compressed air. Oxygen must never be used with air-line respirators, as violent explosions can occur if pure oxygen comes in contact with dirt and oil.

Breathing air may be supplied to respirators from cylinders or air compressors. Cylinders must be tested and maintained as prescribed in the Shipping Container Specification Regulations of the Department of Transportation (49 CFR Part 173 and 178). Cylinders must be marked "breathing air".

The compressors used to supply breathing air to respirators are to be constructed and situated so as to:

• Prevent entry of contaminated air into the air-supply system.
  
  
• Minimize moisture content so that the dew point at 1 atmosphere pressure is 10 °F (5.56 °C) below the ambient temperature.
  
  
• Have suitable in-line air-purifying sorbent beds and filters to further ensure breathing air quality. Sorbent beds and filters shall be maintained and replaced or refurbished periodically following the manufacturer's instructions.
  
  
• Have a tag containing the most recent change date and the signature of the person authorized by the employer to perform the change. The tag shall be maintained at the compressor.
  

For compressors that are not oil-lubricated, the employer must ensure that carbon monoxide levels in the breathing air do not exceed 10 ppm.

For oil-lubricated compressors, a high-temperature or carbon monoxide alarm, or both, should be used to monitor carbon monoxide levels. If only high-temperature alarms are used, the air supply must be monitored at intervals sufficient to prevent carbon monoxide in the breathing air from exceeding 10 ppm.

Breathing air couplings must be incompatible with outlets for nonrespirable worksite air or other gas systems. No asphyxiating substance is to be introduced into breathing air lines.

Breathing gas containers must be marked in accordance with the NIOSH respirator certification standard, 42 CFR part 84.

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