A mask fit test is a specialized procedure designed to verify that a tight-fitting respiratory device forms a secure seal against the wearer’s face. This test confirms that a specific make, model, and size of respirator provides the intended level of protection against airborne hazards. The process ensures air is drawn through the mask’s filter material, not leaking around the edges of the facepiece. This is accomplished by exposing the wearer to a controlled environment while measuring any air leakage along the seal.
The Necessity of Mask Fit Testing
Ensuring a perfect seal is paramount because even a small gap between the respirator and the skin can compromise filtration capabilities. When a tight-fitting mask does not fit correctly, contaminants bypass the filter and enter the wearer’s breathing zone, defeating the purpose of the protection. A proper fit is especially important when workers are exposed to fine dust, aerosols, or pathogenic particles.
Regulatory bodies often require this testing for employees who use tight-fitting respirators, such as filtering facepieces or elastomeric half-mask respirators. The test must be performed before a respirator is used in a hazardous environment and should be repeated at least annually. A new test is also required any time there is a change to the type or size of the respirator used, or if the wearer experiences a significant change in facial structure due to weight fluctuation or major dental work.
Different Types of Fit Testing Procedures
Two primary methods exist for conducting a mask fit test, each confirming the integrity of the seal differently. The first is the Qualitative Fit Test (QLFT), which relies on the wearer’s subjective senses to detect leakage. This method uses a non-toxic test agent, often an aerosolized sweet substance like saccharin or a bitter one like Bitrex, introduced into a hood placed over the wearer’s head. If the wearer can taste the agent while performing movements, it indicates a breach in the seal and results in a test failure.
QLFT is a simple pass/fail assessment typically used for half-mask respirators. A second, more objective approach is the Quantitative Fit Test (QNFT), which utilizes specialized equipment to numerically measure the actual amount of leakage.
QNFT uses an instrument, such as an Ambient Particle Counting device, which measures the concentration of ambient particles both inside and outside the mask simultaneously. The resulting measurement is called a “Fit Factor,” calculated as the ratio of the external particle concentration to the internal particle concentration. For a half-mask respirator to pass, it must achieve a minimum Fit Factor of 100. This quantitative measurement removes the subjectivity inherent in the taste or smell-based QLFT method, providing a precise, data-driven result.
What to Expect During the Test
Before the test begins, the individual must be clean-shaven where the mask’s sealing surface rests against the skin, as facial hair disrupts the seal. The wearer should also avoid eating, drinking anything other than water, or smoking for 15 to 30 minutes immediately prior to the procedure. Once the correct size and model of respirator is selected and properly donned, the test administrator guides the wearer through a sequence of standardized exercises.
These movements simulate the range of motion and activities that occur during a typical workday to ensure the seal remains secure under dynamic conditions. The protocol involves performing actions for a specified duration, such as normal breathing, deep breathing, turning the head side to side and up and down. The wearer also performs a talking exercise, often by reading a passage aloud, and a movement like bending at the waist or jogging in place.
Throughout the required sequence of movements, the seal is continuously monitored either by the wearer reporting detection of the test agent (QLFT) or by the specialized machine recording the Fit Factor (QNFT). A successful test confirms that the chosen respirator size and model provides an adequate seal throughout all simulated workplace activities. If the test fails, the mask must be adjusted, a different size or alternative model must be selected, and the entire testing process repeated.