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102-275
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MFL Occupational Health Centre, Inc. |
Selection of an appropriate respirator is an essential element of a respiratory protection program that also includes hazard evaluation, medical certification, respirator fit tests, cleaning/maintenance/storage, training, record keeping and program evaluation. If an inappropriate respirator is selected, a worker may have a false sense of security and her/his health may be at risk. Of course, a respiratory protection program should only be established after it is determined that engineering or administrative controls are not feasible or are unable to satisfactorily control airborne contaminants.
To select a respirator, first become familiar with the different respirator types. Then gather information regarding contaminants, work environment and worker parameters, remembering to include routine, emergency response (spill clean up) and non-routine (maintenance) activities.
Respirators can be divided into two general classes depending on the method used to provide "clean" air:
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air-purifying: uses filters and/or chemical cartridges and canisters to remove air contaminants. atmosphere-supplying: supplies breathing air to the inside of the facepiece. |
There are many different types of air-purifying respirators. They include single use, reusable half-facepiece or full-facepiece with replaceable filters and/or cartridges and powered air-purifying respirator (PAPR) which have a fan to assist in moving the air through the filtration medium. Specific filters and/or cartridges and canisters are used for different contaminants and contaminant combinations.
The air for atmosphere-supplying respirators may come from bottled air or from special air compressors that filter the ambient air. (Shop compressed air cannot be used.) Breathing air may be carried in tanks on a user's back, as in the self-contained breathing apparatus (SCBA) used by firefighters or supplied through air-lines attached to the facepiece (supplied-air respirator).
Most atmosphere-supplying respirators operate in the positive pressure mode, where air flows continuously to maintain a positive pressure inside the facepiece, reducing the potential for inward leaks of contaminated air. Pressure demand atmosphere-supplying respirators maintain a minimum positive pressure and supply additional air on "demand" (during inhalation), conserving the breathing air.
Respirator types may also be used in combination. For example, a supplied-air respirator can be made with either chemical cartridges or a SCBA as a back up system in case the air-line fails. There are several styles of respirator facepieces. Commonly used types include:
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half-facepiece: forms a tight seal and covers the nose and chin; full-facepiece: forms a tight seal and covers the entire face and chin (providing a higher level of protection while protecting the eyes and face); loose fitting facepiece/visor: forms a partial seal with the face and does not cover the neck and shoulders (may provide eye and/or head protection) helmet or hood: covers head, neck and sometimes the shoulders (may provide head and/or eye protection) |
Respirator selection is also based on the level of protection needed. Each type of respirator is given an assigned protection factor (APF) based on the level of protection provided. Both the facepiece and the method of providing "clean" air contribute to the APF. APFs range from 10 for a half-facepiece air-purifying respirator to 1000 for certain PAPR and atmosphere-supplying respirators.
APFs are used in conjunction with the occupational exposure limits (OELs) to determine the maximum use concentration (MUC), or, in other words, the maximum contaminant air concentration under which the respirator can be used.
APF x OEL = MUC
To ensure protection use only approved (certified) respirators. In North America respirators are approved by two United States agencies: the National Institute for Occupational Safety and Health (NIOSH) and Mine Safety and Health Administration (MSHA). Certification is invalidated if parts from different respirators are interchanged.
Critical to proper respirator selection is the identity and air concentration of the air contaminants requiring respiratory protection, as well as other contaminants that may be present. Contaminant air concentrations must be considered for the complete range of work conditions including routine, non-routine, emergency, seasonal and process differences, as well as immediate danger to life and health (IDLH) conditions. Along with the identity and air concentration, the air contaminant's form (gas/vapour, dust, mist, fume or a combination) will influence the selection of the respirator type, and for air-purifying respirators, dictate the type of filter or chemical cartridge needed. A combination air-purifying cartridge may be needed when providing respiratory protection from more than one contaminant and/or chemical form.
Other chemical exposure routes must be factored into the respirator selection process. For example, skin adsorption may contribute to the worker's overall exposure. If there is potential risk of skin or eye contact, then a full-facepiece is needed to protect the face and eyes. Air-purifying respirators with chemical cartridges can only be used for protection against chemicals with adequate warning properties. Warning properties are odour, taste, or irritation effects associated with a chemical air contaminant. If contaminant are detected inside the respirator either a new chemical cartridge or canister is needed, the facepiece is not fitting properly or the respirator is malfunctioning. In other words, if a prospective respirator wearer cannot consistently detect the appropriate property at or below the OEL, then an atmosphere-supplying respirator will be needed.
When evaluating a work environment for respirator use, first ask the question, "Is the oxygen content of the air acceptable under all circumstances when a respirator is to be used?" Acceptable breathing air must contain 19.5% to 21.4% oxygen. Positive-pressure SCBAs or supplied-air respirators in combination with SCBAs are required for oxygen deficient atmospheres (less than 19.5% oxygen). Oxygen enriched atmospheres (greater than 21.4% oxygen) are dangerous and require special precautions.
Evaluation of job demands will reveal several factors to take into account in the respirator selection process. Will the work take place in a confined space? Are there space limitations - for example, is the work taking place in a cramped space or does the respirator need to fit under a welding helmet? Does the work require exertion and will the weight of the respiratory protection equipment be a factor? Does the job require moving across large spaces or on scaffolding? If it does, then airline respirators may not be appropriate.
Respirator use can interfere with verbal communication. Speaking mechanical diaphragms or electronic speech transmission devices (microphones) may be needed if verbal communication is essential during respirator use. The selected respirator must be compatible with other required personal protective equipment, including hard hats, hearing protection devices and eye protection. The frequency and type of respirator use are also important factors. A half-facepiece respirator may be acceptable for occasional use, but if it must be worn every day for a full-shift, a PAPR may be more comfortable and better accepted. In addition, emergency response (including chemical spill, fire, and mine rescue), non-routine tasks and escape situations may require different respirators than those used on a routine basis where working conditions and contaminant air concentrations are known. Environmental conditions such as temperature extremes and humidity may decrease respirator effectiveness, fit and comfort. Cold temperatures may cause supply-air fittings to fail. An atmosphere-supplying or a PAPR may be more comfortable and maintain a better fit in a hot environment then an air-purifying respirator with filters and/or cartridges. Chemical cartridge effectiveness may be reduced under very high humidity.
Several worker-based parameters impact on selecting the proper respirator. A respirator must consistently be comfortable and fit properly. To assess proper fit, a worker wears the respirator in a test atmosphere. There are two types of tests. In the qualitative fit test the user wears the respirator and is exposed to the test substance. If the wearer does not detect the test substance then the respirator is judged to fit. In the quantitative fit test the user again wears the respirator in a test atmosphere. While the respirator is on, a measurement is made of the concentration of test substance inside and outside the respirator. The respirator does not fit if an excessive level of the test substance is found inside the respirator. As there is a wide variety in facial structure, a respirator wearer may need to be fit tested for respirators from several different manufacturers to obtain a proper and comfortable fit. Sometimes, it is necessary to use a different type of facepiece to achieve a proper fit. (For example, a proper fit may be achieved with a full-facepiece when it is not successful with a half-facepiece.
In addition, workers cannot wear a beard with a tight fighting facepiece, because the beard will interfere with the essential respirator facepiece-to-face seal. Other workers may have medical limitations which may limit or preclude respirator use. Workers who need to wear eyeglasses with a full-facepiece will need special respirator-mounted lenses as regular eyeglass temples break the respirator facepiece-to-face seal.
After compiling the pertinent information on contaminant, work environment and worker parameters, the information can be applied to a respirator selection process. Selection flow diagrams or selection tables like those in the Canadian Standards Association Standard CSA Z94.4-93, Selection, Use, and Care of Respirators, assist in this process. Keep in mind that the tables and flow diagrams do not account for all factors that need to be considered with selection a proper respirator.
For more information on respirator selection and respirator programs see the CSA standard mentioned above or additional references at the MFL Occupational Health Centre Library.
June 1994
