OSHA Respirator Key Definitions

Air-purifying respirator. A respirator with an air-purifying filter, cartridge or canister that removes specific air contaminants by passing ambient air through the air-purifying element.

Assigned protection factor (APF). The workplace level of respiratory protection that a respirator or class of respirators is expected to provide to employees when the employer implements a continuing, effective respiratory protection program as specified by the respiratory protection standard.

key OSHA definitions

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

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

Emergency situation. Any occurrence such as, but not limited to, equipment failure, rupture of containers, or failure of control equipment that may or does result in an uncontrolled substantial release of an airborne contaminant.

End-of-service-life indicator (ESLI). A system that warns the respirator user of the approach of the end of adequate respiratory protection, for example, that the sorbent is approaching saturation or is no longer effective.

Escape-only respirator. A respirator intended to be used only for emergency exit.

Filtering facepiece (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. Filter or air-purifying element. A component used in respirators to remove solid or liquid aerosols from the inspired (inhaled) air.

Fit factor. A quantitative estimate of the fit of a particular respirator to a specific individual, and 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 or a respirator on an individual. See also Qualitative fit test (QLFT) and Quantitative fit test (QNFT).

Helmet. A rigid respiratory inlet covering that also provides head protection against impact and penetration.

High-efficiency particulate air (HEPA) filter. A filter that is at least 99.97 percent efficient in removing monodisperse particles of 0.3 micrometers in diameter and larger. The equivalent NIOSH 42 CFR Part 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 and health (IDLH). An HAZWOPER 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.

Interior structural fire fighting. The physical activity of fire suppression, rescue or both inside of buildings or enclosed structures that are involved in a fire situation beyond the incipient stage.

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

Maximum use concentration (MUC). The maximum atmospheric concentration of a hazardous substance from which an employee can be expected to be protected when wearing a respirator, and is determined by the assigned protection factor of the respirator or class of respirators and the exposure limit of the hazardous substance. 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.

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

Oxygen deficient atmosphere. An atmosphere with an oxygen content below 19.5 percent by volume.

Physician or other licensed health care professional (PLHCP). An individual whose legally permitted scope of practice (i.e., license, registration or certification) allows him or her to independently provide, or be delegated the responsibility to provide, some or all of the health care services required by 29 CFR 1910.134(e), “Medical evaluation.”

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.

Training 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 respiratory 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.

Respiratory inlet covering. The portion of a respirator that forms the protective barrier between the user’s respiratory tract and an air-purifying device or breathing air source, or both. It may be a facepiece, helmet, hood, suit or a mouthpiece respirator with nose clamp.

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

Service life. The period of time that a respirator, filter or sorbent, or other respiratory equipment provides adequate protection to the wearer.

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

Tight-fitting facepiece. A respiratory inlet covering that forms a complete seal with the face. User seal check. An action conducted by the respirator user to determine if the respirator is properly seated on the face.


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