11.0 Glossary


A system consisting of particles, solid or liquid, suspended in air.

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.

Atmosphere-supplying respirator

A respirator that supplies the respirator user with breathing air from a source independent of the ambient atmosphere and includes supplied-air respirators (SARs) and self-contained breathing apparatus (SCBA) units.

Canister (air purifying)

A container filled with sorbents and catalysts that remove gases and vapors from air drawn through the unit. Usually connected to the facepiece with a hose. The canister may also contain an aerosol (particulate) filter to remove particulates.


A small container filled with air-purifying media, attached directly to the respirator facepiece that is designed to remove gases, vapors and/or particulates.


A harmful, irritating or nuisance material that is foreign to the normal atmosphere.

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 significant release of an airborne contaminant.

Employee exposure

Exposure to a concentration of an airborne contaminant that would occur if the employee were not using respiratory protection.

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.

Exhalation valve

A one-way device that permits exhaled air to be discharged from the respirator facepiece.


That portion of a respirator that covers the wearer's nose, mouth and possibly eyes. It is designed to make a gas-tight or dust-tight fit with the face and includes the headbands, exhalation valve(s) and connections for an air-purifying device.


A fibrous medium used in respirators to remove solid or liquid particles from the airstream entering the respiratory enclosure. There are now three particulate filter series available for air purifying respirators;

  • N100, N99 and N95 filters (99.97%, 99% and 95% efficient non-oil filters) to be used with any solid non-oil containing particulate.
  • R100, R99 and R95 filters (99.97%, 99% and 95% efficient oil resistant filters) to be used for any particulate contaminant. If used for an oil containing contaminant, filter use is limited to one work shift only.
  • P100, P99 and P95 filters (99.97%, 99% and 95% efficient oil proof filters) to be used for any particulate contaminant.

Filtering facepiece (dust mask)

A negative pressure particulate respirator with a filter (N95) as an integral part of the facepiece or with the entire facepiece composed of the filtering medium.

Fit factor

A quantitative estimate of respirator fit which 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.

High efficiency particulate air (HEPA) filter

A filter that is at least 99.97% efficient in removing monodispersed particles of 0.3 micrometers in diameter. The equivalent NIOSH 42 CFR 84 particulate filters are the N100, R100, and P100 filters.


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 immediately dangerous to life or health (IDLH). An IDLH atmosphere poses an immediate hazard to life, such as an oxygen deficient atmosphere (containing less than 19.5 percent oxygen), contains explosive or flammable atmospheres, and/or concentrations of toxic substances or produces an irreversible debilitating effect on health.

Inhalation valve

A one-way device that allows purified air to enter the facepiece.

Loose-fitting facepiece

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

Lower explosive limit (LEL)

The lower limit of flammability of a gas or vapor at ordinary ambient temperatures expressed by a percentage of the gas or vapor in air by volume.

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. It is determined by the assigned protection factor of the respirator or class of respirators and the exposure limit of the hazardous substance. The MUC can be determined mathematically by multiplying the assigned protection factor specified for a respirator by the required OSHA permissible exposure limit, short-term exposure limit or ceiling limit.

Mine Safety and Health Administration (MSHA)

A federal agency that, along with NIOSH, tested, approved and certified respiratory protection equipment under the previous 30 CFR Part 11 standard.

National Institute for Occupational Safety and Health (NIOSH)

A federal agency that tested, approved and certified respiratory protection equipment along with MSHA under the old 30 CFR Part 11 standard. NIOSH is now the sole source of approval under the new 42 CFR Part 84 standard.

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 oxygen content below 19.5% by volume.

Permissible exposure limit (PEL)

Maximum permitted airborne chemical concentrations established by OSHA, for compliance purposes, under 29 CFR 1910. The limits are normally published as denoting an 8 hour time weighted average (TWA) value but may also be designated with "C" denoting a ceiling value that is not to be exceeded.

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 paragraph (e) of this section.

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.

Protection factor (PF)

The minimum anticipated protection provided by a properly functioning respirator or class of respirators to a given percentage of properly fitted and trained users.

Rainbow passage

When the sunlight strikes raindrops in the air, they act as a prism and form a rainbow. The rainbow is a division of white light into many beautiful colors. These take the shape of a long round arch, with its path high above, and its two ends apparently beyond the horizon. There is , according to legend, a boiling pot of gold at one end. People look, but no one ever finds it. When a man looks for something beyond his reach, his friends say he is looking for the pot of gold at the end of the rainbow.


Opposition to the flow of air, as through a canister, cartridge or particulate filter.


A device designed to protect the wearer from inhalation of harmful atmospheres.

Respiratory inlet covering

That 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 carried 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 carried by the user.

Threshold limit value (TLV)

A list published the American Conference of Governmental Industrial Hygienists (ACGIH) as a recommended guide for exposure concentrations that a healthy individual normally can tolerate for eight hours a day, five days a week over the duration of a normal working career without harmful effects. Airborne particulate concentrations are generally listed as milligrams per cubic meter of air (mg/m³), and gaseous concentrations are listed as parts per million (ppm) by volume.

Tight-fitting facepiece

A respiratory inlet covering that forms a complete seal with the face.

Warning Properties

A given chemical's ability to be smelled, tasted or exhibit irritation effects at airborne concentrations below the PEL or TLV.

Appendix B