For a respiratory protection program to be effective, the correct respirator must be chosen, and worn appropriately.

To improve the selection process, OSHA has published “Assigned Protection Factors” (APF), a new guidance document that provides employers with vital information for selecting respirators for employees exposed to contaminants in the air.

OSHA revised its existing Respiratory Protection standard (29 CFR 1910.134) in 2006 to add APFs and Maximum Use Concentration (MUC) provisions. APF means the workplace level of respiratory protection that a respirator or class of respirators is able to provide to workers.

The higher the APF number (5 to 10,000), the greater the level of protection provided to the user. APFs are used to select the appropriate class of respirators that will provide the necessary level of protection against airborne contaminants. Such exposures can come from particles or a gas or vapor.

MUC represents the limit at which the class of respirator is expected to provide protection. Whenever a hazard’s exposure level exceeds MUC, employers should select a respirator with a higher APF. MUC means the maximum atmospheric concentration of a hazardous substance for which a worker can expect to be protected when wearing a respirator.

“Proper respirator selection prevents exposure to hazardous contaminants and is an important component of an effective respiratory protection program,” said Deputy Assistant Secretary of Labor for OSHA Donald G. Shalhoub. “This guidance document serves as another useful resource for protecting the health and safety of workers at risk for respiratory illnesses.”

APF and MUC are mandatory respirator selection requirements that can only be used after respirators are properly selected and are used in compliance with the entire standard. The Respiratory Protection standard requires fit testing, medical evaluations, specific training and proper respirator use. The standard applies to general industry, construction, long-shoring, shipyard and marine terminal workplaces.

The MUC usually can be determined mathematically by multiplying the assigned protection factor specified for a respirator by the permissible exposure limit (PEL), short-term exposure limit, ceiling limit, peak limit, or any other exposure limit used for the hazardous substance.

The MUC for respirators is calculated by multiplying the APF for the respirator by the PEL. The MUC is the upper limit at which the class of respirator is expected to provide protection. Whenever the exposures approach the MUC, then the employer should select the next higher class of respirators for the employees.

Employers must not apply MUCs to conditions that are immediately dangerous to life or health (IDLH); instead, they must use respirators listed for IDLH conditions in paragraph (d)(2) of the standard.

When the calculated MUC exceeds the IDLH level for a hazardous substance, or the performance limits of the cartridge or canister, then employers must set the maximum MUC at that lower limit.

How to use APFs and MUCs

Under the Respiratory Protection standard, APFs and MUCs are used specifically in selecting proper equipment under section (d)(3), which addresses the selection of respiratory protection equipment for non-IDLH atmospheres.

In this provision, under (d)(3)(i), employers must provide respirators that are adequate to protect employee health and ensure compliance with all other OSHA requirements under routine, and reasonably foreseeable, emergency situations.

Under paragraph (d)(3)(i)(A), employers must select respirators according to APFs. Under paragraph (d)(3)(i)(B), employers must select respirators after considering the MUCs in their workplace under which respirators are to be used. Under paragraph (d)(3)(ii), employers must select respirators (using APFs as well) that are appropriate for the chemical state and physical form of the contaminant.

You need different types of filters, cartridges, and canisters depending on whether dusts, fumes, mists, vapors or gases are present in your workplace and depending on the kinds and concentrations of the substances present.

Respiratory hazards may be present in the workplace whenever an atmosphere does not contain sufficient oxygen, or if it contains chemical, biological, or radiological contaminants in sufficient quantity to harm the health of employees. Respiratory hazards may be present in the workplace in the following physical forms:

Dusts and fibers are solid particles that are formed or generated from solid materials through mechanical processes such as crushing, grinding, drilling, abrading or blasting. Examples are lead, silica and asbestos.

Fumes are solid particles that are formed when a metal or other solid vaporizes and the molecules condense (or solidify) in cool air. Examples are metal fumes from smelting or welding. Fumes also may be formed from processes such as plastic injection or extrusion molding.

Mists are tiny droplets of liquid suspended in the air. Examples are oil mist produced from lubricants used in metal cutting operations, acid mists from electroplating, and paint spray mist from spraying operations.

Gases are materials that exist as individual molecules in the air at room temperature. Examples are welding gases, such as acetylene and nitrogen, and carbon monoxide produced from internal combustion engines.

Vapors are the gaseous form of substances that are normally in the solid or liquid state at room temperature and pressure. They are formed by evaporation.

Most solvents produce vapors. Examples include toluene and methylene chloride.

Biological hazards include bacteria, viruses, fungi, and other living organisms that are respirable and can cause acute and chronic infections. Examples include Legionnaire’s Disease and animal waste products (e.g., feces).

Types of Respirators

The major types of respirators include air-purifying respirators and atmosphere supplying respirators. An air-purifying respirator is a respirator with an air-purifying filter, cartridge, or canister that removes specific air contaminants by passing ambient air through the air-purifying element.

An atmosphere-supplying respirator supplies the respirator user with breathing air from a source independent of the ambient atmosphere, and includes SARs and SCBA units.

To determine the protection provided by a respirator during use, a protection factor study should be undertaken. This determination generally is accomplished by measuring the ratio of the concentration of an airborne contaminant (e.g., hazardous substance) outside the respirator (Co) to the concentration inside the respirator (Ci) (i.e., Co/Ci). Therefore, as the ratio between Co and Ci increases, the protection factor increases, indicating an increase in the level of protection provided to employees by the respirator.

The four types of protection factor studies are:

Effective Protection Factor (EPF) study — a study conducted in the workplace that measures the protection provided by a properly selected, fit tested, and functioning respirator when used intermittently for only some fraction of the total workplace exposure time (i.e., sampling is conducted during periods when respirators are worn and not worn). EPFs are not directly comparable to WPF values because the determinations include both the time spent in contaminated atmospheres with and without respiratory protection; therefore, EPFs usually underestimate the protection afforded by a respirator that is used continuously in the workplace.

Program Protection Factor (PPF) study — a study that estimates the protection provided by a respirator within a specific respirator program. Like the EPF, it is focused not only on the respirator’s performance, but also the effectiveness of the complete respirator program. PPFs are affected by all factors of the program, including respirator selection and maintenance, user training and motivation, work activities, and program administration.

Workplace Protection Factor (WPF) study — a study, conducted under actual conditions of use in the workplace, that measures the protection provided by a properly selected, fit tested, and functioning respirator, when the respirator is worn correctly and used as part of a comprehensive respirator program that is in compliance with OSHA’s Respiratory Protection standard at 29 CFR 1910.134.

Measurements of Co and Ci are obtained only while the respirator is being worn during performance of normal work tasks (i.e., samples are not collected when the respirator is not being worn). As the degree of protection afforded by the respirator increases, the WPF increases.

Simulated Workplace Protection Factor (SWPF) study — a study, conducted in a controlled laboratory setting and in which Co and Ci sampling is performed while the respirator user performs a series of set exercises. The laboratory setting is used to control many of the variables found in workplace studies, while the exercises simulate the work activities of respirator users. This type of study is designed to determine the optimum performance of respirators by reducing the impact of sources of variability through maintenance of tightly controlled study conditions.

Glossary of Terms Other terms users should be familiar with include the following:

Canister or cartridge: A container with a filter, sorbent, or catalyst, or combination of these items that removes specific contaminants from the air passed through the container.

Continuous flow respirator: An atmosphere- supplying respirator that provides a continuous flow of breathable air to the respirator facepiece.

Demand respirator: An atmospheresupplying respirator that admits breathing air to the facepiece only when a negative pressure is created inside the facepiece by inhalation.

Dioctylphthalate (DOP): An aerosolized agent used for quantitative fit testing.

Elastomeric: A respirator facepiece made of a natural or synthetic elastic material such as natural rubber, silicone, or EPDM rubber.

Filter or air-purifying element: A component used in respirators to remove solid or liquid aerosols from the inspired air.

Filtering facepiece (or dust mask): A negative pressure particulate respirator with a filter as an integral part of the facepiece or with the entire facepiece composed of the filtering medium.

Fit factor: A quantitative estimate of the fit of a particular respirator to a specific individual that typically estimates the ratio of the concentration of a substance in ambient air to its concentration inside the respirator when worn.

Fit test: The use of a protocol to qualitatively or quantitatively evaluate the fit of a respirator on an individual. Helmet: A rigid respiratory inlet covering that also provides head protection against impact and penetration.

High efficiency particulate air filter (HEPA): A filter that is at least 99.97 percent efficient in removing monodisperse particles of 0.3 micrometers in diameter. The equivalent NIOSH 42 CFR 84 particulate filters are the N100, R100, and P100 filters.

Hood: A respiratory inlet covering that completely covers the head and neck and may also cover portions of the shoulders and torso. Immediately dangerous to life or health (IDLH): An atmosphere that poses an immediate threat to life, would cause irreversible adverse health effects, or would impair an individual’s ability to escape from a dangerous atmosphere.

Loose-fitting facepiece: A respiratory inlet covering that is designed to form a partial seal with the face.

Negative pressure respirator (tightfitting): A respirator in which the air pressure inside the facepiece is negative during inhalation with respect to the ambient air pressure outside the respirator.

Permissible Exposure Limit (PEL): An occupational exposure limit specified by OSHA. Positive pressure respirator: A respirator in which the pressure inside the respiratory inlet covering exceeds the ambient air pressure outside the respirator.

Powered air-purifying respirator (PAPR): An air-purifying respirator that uses a blower to force the ambient air through air-purifying elements to the inlet covering.

Pressure demand respirator: A positive pressure atmosphere-supplying respirator that admits breathing air to the facepiece when the positive pressure is reduced inside the facepiece by inhalation.

Qualitative fit test (QLFT): A pass/fail fit test to assess the adequacy of respirator fit that relies on the individual’s response to the test agent.

Quantitative fit test (QNFT): An assessment of the adequacy of respirator fit by numerically measuring the amount of leakage into the respirator.

Recommended Exposure Limit (REL): An occupational exposure level recommended by NIOSH.

Respirator Decision Logic (RDL): Respirator selection guidance developed by NIOSH that contains a set of respirator protection factors.

Self-contained breathing apparatus (SCBA): An atmosphere-supplying respirator for which the breathing air source is designed to be carried by the user.

Supplied-air respirator (or airline) respirator (SAR): An atmosphere-supplying respirator for which the source of breathing air is not designed to be carried by the user.

Threshold Limit Value (TLV): An occupational exposure level recommended by ACGIH. Tight-fitting facepiece: A respiratory inlet covering that forms a complete seal with the face. FSM