Mask fit testing is part of the respiratory protection protocol on hazardous work sites once hazards have been identified. (Learn more in "Introduction to Hazard Identification Studies".) Employees are required to wear protective face pieces that will limit their exposure to contaminants and irritants while on the job.

To do this, a protective face piece known as a respirator is used. A respirator is a breathing apparatus that is used to limit the inhalation of fumes, smoke, dust, or other toxic substances on the premises. A mask fit test is a procedure carried out to make sure that the respirator fits the user's face correctly.

Mask fit testing is administered on work sites where there is the presence of hazardous materials and the risk of exposure is elevated. The purpose of the fit test is to make sure that the device fits well without having any leaks.

Types of Respirators

There are a two main types of protective respiratory devices available. These are air purifying respirators and atmosphere supplying respirators. Depending on the industry, employers can choose one that best suits their industry’s safety requirement. Air purifying respirators work by preventing respirable particles from reaching the breather through filtration.

• Air purifying respirators, half masks: Half masks only provide protection over the nose and chin, exempting protection for the eyes. These types are more suitable for environments with lower concentrations of toxins or contaminants that are a hazard to the lungs only.
• Air purifying respirators, full masks: In comparison, full face masks are designed to cover the entire face but are also heavier than their half face counterparts. And while this may add to the element of discomfort while wearing the respirator, this type is recommended for environments where greater eye protection is required along with more respiratory protection.

Both types of air purifying respirators have cartridges or filters that remove contaminants from the surrounding environment, and should not be used in settings where there is an oxygen deficiency, in an area of elevated concentration of contaminants, or where contaminates can not be filtered safely.

• Atmosphere supplying respirators: Workers who are employed in industries with heavy contamination or contamination that can not be easily filtered can use respirators that source air from a source different than the surrounding air. In these cases, the respirator is not just a simple mask but one attached to a separate source of clean air. The clean air can be supplied via a hose or from a self contained air unit carried by the breather.

Clean, fresh air is provided to the wearer from an outside, uncontaminated source such as a cylinder allowing longer term usage. This type of respirator is suitable to use in oxygen deficient atmospheres and in areas with high contamination.

General Requirements for Mask Fit Testing

Regardless of the type of respirator or mask used, the mask fit test is a safety requirement for specific types of jobs and comes with a set of OSHA regulations that need to be followed closely. Among requirements for testing, the following criteria needs to be met accurately:

• The worker has to wear the same mask during the test as on the job.
• In the case of a worker who wears corrective glasses, the same glasses also need to be worn during the test.
• Mask fit tests need to be administered prior to starting a job that requires wearing a respirator.
• Tests are conducted annually to ensure proper fitting.
• Should a worker gain or lose weight, grow facial hair or undergo facial/ dental surgery, the fit test needs to be redone to ensure correct fitting.
• Subjects with facial hair need to remove hair that would fall under the mask seal before testing and work. (Learn more in "Do I have to shave my beard for mask fit testing?")
• The subject cannot eat, drink, or smoke 20 minutes prior to the test.

Types of Mask Fit Tests

There are two different types of mask fit tests that are administered in different work settings. The first of these is called the qualitative fit test which is the more common of the two. This test checks the effectiveness of typically used workplace masks such the N95 respirator.

The N95 respirator is a piece of personal protective equipment (PPE) used on worksites where exposure to airborne and liquid particles is likely. The respirator can come in two forms, either covering the full face or only half the face.

For a mask fit test to be successful, the respirator needs to provide a very close facial fit to protect against the risk of contamination.

Qualitative Mask Fit Test

The qualitative mask test is done to assess how effective the device is for protection against different types of leaks. Testing uses different agents that have either a specific smell or taste and measures the subject's reaction to these agents. For instance, if the subject is able to detect taste or smell at a concentration outside of accepted standards, the fit test fails and a different device needs to be tested. Qualitative mask testing also considers the element of reaction to an irritant. It is typically used for half face devices. In the case of these irritants, reactions are monitored and compared against a chart of standards. This type of test yields a pass or fail result based on how effective the protective device is in regulating leakage to the subject's face. (Learn more in "What kind of smoke is used in mask fit testing?")

OSHA accepts four standards for this type of testing:

• Asoamyl acetate- smells like bananas
• Saccharin- leaves a bitter sweet taste in the mouth
• Bitrex- leaves a bitter taste in the mouth
• Irritant smoke- can cause coughing

Quantitative Mask Fit Test

The second type of mask fit test is called the quantitative fit test and does not measure leakage by breather reaction. Instead, testing uses a device to calculate the actual amount of leakage into the respirator. This type of test is administered for checking the efficacy of full face respirators.

OSHA accepts three methods for this type of testing:

• Generated aerosol
• Ambient aerosol
• Controlled negative pressure

Importance of Regular Mask Fit Testing

OSHA requires regular mask fit testing is because breather features may change, work atmosphere risks may change, and masks can wear out or be damaged over time. Any failure of PPE could have serious repercussions to worker safety, productivity rates, and Workers' Compensation costs. (Learn more in "Why Fit Testing is Important for Workers Wearing Personal Protective Equipment (PPE)".)

A study conducted by the National Institute for Occupational Safety and Health (NIOSH) involved more than 100 participants over a span of three years. The study worked with different types of respirators and evaluated how changes in facial features, weight loss, and weight gain could affect the integrity of the respirator.

Results of the study showed that regular fit tests needed to be done to preserve the integrity and safety of the protective devices. In fact, with longer gaps between the tests, participants were at a greater risk for a misfit and higher risk of exposure to occupational contaminants.