Respirator Fit Study FAQ – Background on Respirators & Fit Testing

What are air-filtering respirators?

There are many types of respirators. Respirators are often separated by how they provide clean air and are classified as air-purifying or air-supplying respirators.

Air-purifying respirators use a filtering mechanism to clean “dirty” air before the worker breathes it in. For bioaerosols this involves using HEPA filters, called cartridges, or disposable respirators made of HEPA material (e.g., N95). These respirators can be non-powered (i.e., worker required to breathe through filters) or powered (i.e., a power source pushes air through the filters for the worker).

Air-supplying respirators provide a source of clean air that is delivered to the wearer. This is done by carrying an air tank where the worker moves (i.e., self-contained breathing apparatus) or by being connected to an airline that provides clean air from an area away from the hazard.

What are tight-fitting respirators?

Tight-fitting respirators are respirators that require a tight seal between the respirator and the wearer’s face to work properly. Some examples include filtering face-piece respirators like N95s, elastomeric half and full face-piece respirators, tight-fitting powered-air purifying respirators, self-contained breathing apparatus.

What is respirator fit testing?

Respirator fit testing measures how well a respirator fits a wearer and verifies if the respirator provides the wearer with the expected level of protection. This includes the comfort and seal of the respirator. There are two kinds of fit tests:

  • A qualitative fit test relies on the wearer’s sense of smell and/or taste to detect a chemical when exposed when wearing a respirator. This may include a bitter or sweet chemical. This fit test only provides a yes/no answer to the fit, i.e., qualitative.
  • A quantitative fit test provides a ratio of the number of particles outside and inside the respirator to measure how well the respirator filters particles. This does not rely on the users’ senses and provides a fit factor number, i.e., quantitative.

How is a fit check different from a fit test?

A fit check, also known as a user seal check, is a test done to determine if the respirator is donned correctly by the wearer and the respirator has a good seal.  This is conducted every time a respirator is put on (i.e., donned) and does not require chemicals or equipment. There are two checks to be performed:

  • Positive pressure fit check—A positive pressure environment is created inside the respirator by exhaling gently while blocking the exhalation valve (i.e., where the air leaves the respirator). A successful check is when the respirator bulges slightly without air leaking out.
  • Negative pressure fit check— A negative pressure environment is created inside the respirator by inhaling gently while blocking the inhalation valves (i.e., cartridges where air enters the respirator). A successful check is when the respirator collapses slightly without air leaking out.

How often should I conduct a fit check?

Once a fit test is passed successfully, you should complete a fit check/user seal check every time you put on a respirator to ensure an adequate seal is achieved.

How often should I be fit tested?

The CSA Z94 recommends fit testing being conducted at least every two years after initial testing.  Fit testing should also be conducted when:

  • You change the type of respirator you wear, including the make/model/size
  • You experience a change in comfort in wearing the respirator
  • You have a physical change in your appearance that may change the shape of your face
    • Weight change (loss/gain)
    • Facial scarring, disfiguration, or piercing
    • Significant dental work or dental changes (e.g., dentures)