Respiratory Protection

The Respiratory Protection Standard (29 CFR 1910.134) makes for certain requirements depending on whether respirators are required by the employer and the types of respirators being used. The flowchart included at the bottom of this article is a quick way to determine these requirements.

What Is a Respirator?

Respirators include SCBA, supplied air — including even the simple filtering facepiece (dust mask).

How do filters collect particles?

Figure 1: Filtration mechanisms

These capture — or filtration — mechanisms are described as follows:

Inertial impaction: With this mechanism, particles having too much inertia due to size or mass cannot follow the airstream as it is diverted around a filter fiber. This mechanism is responsible for collecting larger particles.

Interception: As particles pass close to a filter fiber, they may be intercepted by the fiber. Again, this mechanism is responsible for collecting larger particles.

Diffusion: Small particles are constantly bombarded by air molecules, which causes them to deviate from the airstream and come into contact with a filter fiber. This mechanism is responsible for collecting smaller particles.

Electrostatic attraction: Oppositely charged particles are attracted to a charged fiber. This collection mechanism does not favor a certain particle size.

Classification of Respirators

There are two ways to provide clean air to the individual wearing the respirator:

• Purify the air surrounding the employee;
• Supply clean air from an outside source.

Air-Purifying Respirators

There are three methods of purifying, or filtering, the air:

• Particulate — Filtering particles from the air based on size.
• Gas/Vapor — Absorption/adsorption of a toxic substance that is too small to be caught by particulate filters.
• Combination — This is simply a combination of the two methods above. Usually, one type of cartridge is stacked in series with the other type of cartridge.

Atmosphere-Supplying Respirators

There are also three ways to supply pre-cleaned air to the wearer:

• Air-Supplied / Supplied-Air / Atmosphere-Supplying Respirators
• Self-Contained Breathing Apparatus (SCBA)
• Combination Respirators

Physical/Dimensional Characteristics

In addition to classifying respirators by the method of providing clean air to the employee, respirators can be classified by the physical/dimensional characteristics of the respirator itself.

• Disposable vs. Reusable
• Facepiece: "Half Mask" vs. "Full" vs. "Quarter"
  • The quarter is rarely used.
• Powered
• Supplied-Air

Source: OSHA's Small Entity Compliance Guide for the Respiratory Standard

Assigned Protection Factors (APF)

The following table lists the APF of the different types of respirators.

The APF is a factor that is used to determine the maximum airborne levels of a toxin that a certain type of respirator can protect against. For example, if the PEL of a certain toxin is 10 mg/m³ and the type of respirator provides an APF of 10, then the maximum levels of that toxin that an employee can use that respirator safely is 100 mg/m³.

Source: OSHA's Small Entity Compliance Guide for the Respiratory Standard

Terminology Not Covered Elsewhere

• Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface.[1] This process creates a film of the adsorbate on the surface of the adsorbent.  This process differs from absorption, in which a fluid (the absorbate) permeates or is dissolved by a liquid or solid (the absorbent).[2] Adsorption is a surface-based process while absorption involves the whole volume of the material. The term sorption encompasses both processes, while desorption is the reverse of it. Adsorption is a surface phenomenon.

Oil-Tolerance Letter Designation for Particulate Filters

The following information was pulled from NIOSH Respirator Selection Logic.

9.2. A filter series (N, R or P) that will provide protection against exposure to the particulate in question is recommended.

a. The selection of N-, R-, and P-series filters depends on the presence or absence of oil particles, as follows:

• If no oil particles are present in the work environment, use a filter of any series (i.e., N-, R-, or P-series).
• If oil particles (e.g., lubricants, cutting fluids, glycerine, etc.) are present, use an R- or P-series filter. Note: N-series filters cannot be used if oil particles are present.
• If oil particles are present and the filter is to be used for more than one work shift, use only a P-series filter.

b. Selection of filter efficiency (i.e., 95%, 99%, or 99.97%) depends on how much filter leakage can be accepted. Higher filter efficiency means lower filter leakage.

Note: To help you remember the filter series, use the following guide:

• N for Not resistant to oil,
• R for Resistant to oil
• P for oil Proof

Additional information on selecting the appropriate filter certified under 42CFR84 can be found at http://www.cdc.gov/NIOSH/userguid.html.

Other Resources

• OSHA's Safety and Health Topics | Respiratory Protection - General Guidance