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Quick Guide: Mask Fit Testing

Respirators play a vital role in protecting workers from harmful airborne contaminants, including dust, gases, vapours, fumes, chemicals, and infectious agents.

To provide optimal protection, tight-fitting respirators rely on an adequate seal between the facepiece and the wearer's face. An inadequate fit can result in leakage putting the wearer at risk of

breathing in harmful, contaminants

Credit: TSI

To ensure proper fit, respirator fit testing is essential.

In this post, we'll explore the importance of fit testing, the two primary methods – qualitative and quantitative, and how they align with the AS/NZS 1715:2009 standard.

The Importance of Respirator Fit Testing

Respirator fit testing is a critical component of any comprehensive respiratory protection program. Its primary objective is to determine if a specific respirator model and size fits a particular individual properly.

Fit testing is essential for several reasons:

1. Ensure adequate protection: An ill-fitting respirator can allow contaminants to enter the breathing zone, putting the wearer at risk.

2. Promote comfort: A well-fitted respirator is more comfortable, increasing the likelihood that workers will wear it consistently and correctly.

3. Compliance: The AS/NZS 1715:2009 notes that fit testing is required as part of any respiratory protection program where workers must wear tight-fitting respirators. Failure to comply can result in fines and penalties.

Does a Tiny Little Leak Really Matter?

Often, folks will pop on their respirator and it seems to fit right. It feels comfortable (as comfortable as a respirator can feel), it looks like it fits and they can't detect any obvious leaks.

But beware. Just because a respirator looks and feels OK, this doesn't mean it's achieving an appropriate seal. It's impossible to visually detect a tiny leak between the respirator's facepiece and the face (that's what the fit test does).

Many workplace airborne hazards are unimaginably small. Very small things have no problem finding a break in the seal of a respirator and making their way into the breathing zone. Even the tiniest leak in a respirator can let in hundreds to millions of submicron particles, gases or vapours.

Take a look at the graphic below. Really small things are measured in microns (a micron is 1/1000 of a millimeter). A single grain of beach sand is around 90 microns. Dust particles, such as silica dust, can be 2.5 microns and smaller. Viruses, like a coronavirus, also fall at the end of this spectrum.

Credit: Virtual Capitalist

Particles less than 10 microns bypass the body's upper airway defenses (coughing, sneezing, mucociliary clearance) and go straight to the lungs.

Particles less than 2.5 microns go even deeper. They penetrate into the alveoli (air sacs) and can cross over into the bloodstream and may cause widespread, systemic effects in the body.

Another property of submicron particles is that they stay suspended in the air - sometimes for hours.

So yes, even a tiny compromise in the respirator can be a big problem. That's why respirators need to be fit-tested.

Fit Test Methods

The two primary types of fit testing are the qualitative and quantitative methods.

Qualitative methods, such as Bitrex or saccharin solution taste testing, rely on the wearer's sensory perception, making them relatively straightforward and cost-effective. However, they are subjective and can't provide as precise results as quantitative methods.

Quantitative methods offer objective, numerical data, allowing for a more accurate assessment of respirator fit. While quantitative methods are generally more complex and require specialized equipment, the results are more reliable.

The choice between qualitative and quantitative fit testing should be based on factors such as the respirator type, workplace hazards, and regulatory requirements. Full face respirators must always be tested using a quantitative fit test method.

Qualitative Fit Test Method Using Bitrix of saccharin tasting spray. Credit: Canva

Qualitative Fit Testing

Qualitative fit testing is a subjective method used to evaluate the fit of a respirator on an individual. This method relies on the wearer's sense of taste, smell, or irritation to detect the presence of a test agent.

The AS/NZS 1715:2009 recognizes qualitative fit testing as an acceptable method for assessing respirator fit for disposable and half-face respirators (full-face respirators must be tested using a quantitative method).

Common qualitative fit testing methods include:

1. Bitrex Taste Test: Bitrex is a bitter-tasting substance that is introduced into a test hood or mask. The wearer performs a series of exercises that may induce respirator leakage. If the wearer detects the taste of Bitrex, it indicates a poor fit.

2. Saccharin Taste Test: Similar to Bitrex, saccharin solution is used to test the respirator's seal. The wearer performs exercises, and if they taste the sweet saccharin solution, it indicates a leak.

3. Irritant Smoke: In this method, a stinging or irritating smoke is introduced into the mask. If the wearer experiences irritation or discomfort, it suggests a poor fit. This method is not typically used in Australia.

All qualitative fit test methods are pass/fail. If someone passes, the assumed fit factor is 100.

Qualitative fit testing is relatively simple and cost-effective. However, because it relies on the wearer's subjective sensory perception, this method is less precise than quantitative methods.

Other challenges with qualitative fit testing (specifically Bitrex and saccharin taste methods):

  • While rare, there is the potential for the fit test solutions to induce allergic reactions or exacerbate an existing condition such as asthma.

  • The fit test hood causes distress for some people.

  • People can cheat the test. For example, if someone just wants to get the test over, they can say they do not taste the solution when they do. Or if someone doesn't like a particular mask that's being tested, they can say they do taste the solution when they really don't.

  • It takes a long time, it's messy and people really dislike the tasting agents (especially Bitrex!).

Quantitative Fit Testing

Quantitative fit testing, on the other hand, provides objective, numerical data to assess the respirator fit accurately. This method utilizes specialized equipment to measure the concentration of particles inside and outside the respirator mask.

Common quantitative fit testing methods include:

1. Condensation Nuclei Counter (CNC): The most widely used quantitative method, this test challenges the seal of the respirator with naturally occurring particles in the ambient air. A machine, such as a PortaCount, measures particles generated by a test aerosol inside and outside the respirator. The fit factor is calculated based on the ratio of these particle concentrations.

2. Controlled Negative Pressure (CNP): This fit test method measures the pressure inside the mask while the wearer performs various exercises. A fit factor is calculated based on the pressure changes.

At Fit Test Victoria, we use PortaCount fit test machines (like the one in the pic below) to conduct the CNC method of fit testing. So let's explore this a little more.

CNC Fit Testing Using the PortaCount

The PortaCount fit test machine provides a highly accurate assessment of how well a respirator seals to a wearer's face. To understand the fit testing process with a PortaCount, it's essential to grasp how the fit factor is calculated.

The fit factor is a numerical value that quantifies the effectiveness of a respirator's seal. It represents the ratio of particle concentrations outside the respirator to those inside the respirator.

Ambient air particle concentration / concentration of particles inside the respirator = fit factor

For disposable and half-face reusable respirators, an overall fit factor of 100 is needed to pass the test. For full-face respirators, a fit factor of 500 is required.

Here's a basic explanation of how the fit factor is calculated during a PortaCount fit test:

1. Baseline Measurement: Before the fit test begins, the PortaCount takes baseline measurements of particle concentrations inside and outside the respirator. These measurements establish the starting point for comparison.

2. Fit Test Sequence: The wearer then undergoes a series of fit test exercises (such as bending, moving head side to side, talking, jogging) based on the chosen fit test protocol. These exercises are designed to simulate real-world conditions that could potentially compromise the respirator seal. In Australia, the most common protocols are the OSHA Fast Filtering Facepiece Protocol (for N95/P2 disposable masks) and the OSHA Fast Half/Full Protocol (for reusable half and full face respirators).

3. Particle Monitoring: Throughout the fit test sequence, the PortaCount continuously monitors particle concentrations both inside and outside the respirator. It does this by counting the number of particles in a specific size range using laser-based technology.

4. Fit Factor Calculation: The fit factor is calculated by comparing the baseline particle concentrations to those recorded during the fit test exercises. Specifically, the PortaCount divides the baseline concentration outside the respirator by the concentration inside the respirator during each exercise. The fit factor for each exercise is determined separately.

5. Overall Fit Factor: Finally, an overall fit factor is calculated by averaging the fit factors from all the exercises. It is possible to fail an exercise and still pass the fit test. The PortaCount is concerned with the overall fit factor.

A fit factor equal to or greater than the minimum required level indicates that the respirator is providing an adequate seal and protecting the wearer against harmful airborne contaminants.

Quantitative fit testing offers a couple of advantages compared to qualitative testing:

  • Objective Data: A numerical calculation objectively assesses the respirator's fit.

  • Reliability: Quantitative methods are generally more precise than qualitative methods. Generally speaking, you can rely on the PortaCount machine but you can't always rely on a person's subjective sense of taste.

Wrapping Up

Respirator fit testing is a crucial element of a comprehensive respiratory protection program. Proper fit ensures that respirators effectively protect workers from hazardous airborne contaminants.

The AS/NZS 1715:2009 provides guidelines for respirator fit testing and recognizes both qualitative and quantitative methods as valid tests.

While qualitative fit testing is subjective, quantitative fit testing offers objective, numerical results. Employers should choose the fit testing method that best suits their needs while ensuring compliance with relevant regulations.

Ultimately, the safety and well-being of workers depend on the proper fit of their respirators, and fit testing is the key to achieving this goal.

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