Respirator fit test

Not to be confused with Respirator seal check.

A respirator fit test checks whether a respirator properly fits the face of a user. A fitting respirator must be able to separate a user's respiratory system from ambient air.

F.H. Varley painting depicts a training exercise in Seaford, England. Soldiers emerge from a gas hut wearing respirators.

The test involves tightly pressing the mask flush against the face (without gaps) to ensure an efficient seal on the mask perimeter. Protection depends on an airtight seal, making testing necessary before entering contaminated air.

Mask size and shape correctly fitted to the user's face, provides better protection in hazardous environments.^[1]

Facial hair such as beards can interfere with proper fit.^[2]

History

Fit test in US Navy

The effectiveness of various types of respirators was measured in laboratories and in the workplace.^[3] These measurements showed that in practice, the effectiveness of negative pressure tight fitting respiratory protective devices (RPD) depends on leakage between mask and face, rather than the filters/canisters.^[4] This decrease in efficiency due to leakage manifested on a large scale during World War I, when gas masks were used to protect against chemical weapons. Poor fit or poorly situated masks could be fatal. The Russian army began to use short-term exposure to chlorine at low concentrations to solve this problem in 1917.^[5][6] Such testing helped convince the soldiers that their gas masks were reliable - because respirators were a novelty.^[7] Later, industrial workers were trained in gas chambers in the USSR (in preparation for the Second World War),^[8][9][10] and late^[11]'. German firefighters used a similar test between the First and Second World Wars.^[12] Diluted chloropicrin was used to test industrial gas masks.^[13] The Soviet Army used chloropicrin in tents with a floor space of 16 square meters.^[14]

Fit test methods

Respirator selection and use is regulated in many countries.^[15][16][17] Regulations often include a test of negative pressure mask for each individual wearer.

Qualitative and quantitative fit test methods (QLFT & QNFT) exist. Detailed descriptions are given in the US standard, developed by the Occupational Safety and Health Administration OSHA.^[15] This standard regulates respirator selection and organization (Appendix A describes fit testing). Compliance with this standard is mandatory for US employers.

Qualitative

Irritant smoke fit test

These methods use the reaction of workers to the taste or smell of a special material (if it leaks into mask) - gas, vapors or aerosols. Such reactions are subjective, requiring the subject to report results honestly. A qualitative fit test starts with an unfiltered/non-respirator sampling of the substance of choice to verify that the subject can detect it accurately. Substances include:

• Isoamyl acetate—This substance has the smell of bananas. It is used only for fit testing of elastomeric masks.^[18]
• Saccharin— Mixed with water and aerosolized, saccharin's sweet taste is used to test elastomeric and filtering respirator masks. The subject breathes through the mouth, slightly sticking out the tongue.
• Denatonium— A substance with a bitter taste that can be used to detect gaps. It is mixed with water and sprayed in the same manner as the above materials.

• Irritant smoke— Irritates mucous membranes resulting in discomfort, coughing, sneezing, etc. NIOSH recommended discontinuing this method, as exposure may significantly exceed the Permissible Exposure Limit (e.g., in the presence of high humidity).^[19]

Quantitative

PortaCount Plus (TSI) - device for ambient aerosol fit test

Air Techniques International TDA-99M used for generated aerosol fit testing

Equipment can determine concentrations of a control substance (challenge agent) inside and outside the mask or determine the flow rate of air under the mask. Quantitative methods are more accurate and reliable than qualitative methods because they do not rely on subjective sensing of the challenge agent. Unlike qualitative methods, quantitative methods provide a data-based, defensible metric.

Ambient aerosol method

An aerosol test measures the internal and external aerosol concentrations. The aerosol can be artificial, or a natural atmospheric component. The ratio of external to internal concentration is the fit factor (FF).^[19] U.S. law requires employers offer employees masks with sufficient fit factor. For half face-piece masks (used when the concentration of harmful substances is not more than 10 PEL), the fit factor must be at least 100; and for full face masks (not more than 50 PEL), the fit factor must be at least 500. The safety factor of 10 compensates for the difference between testing and workplace conditions. To use an atmospheric aerosol one needs a PortaCount or AccuFIT device. These devices increase the size of the smallest particles through a process of vapor condensation (Condensation Particle Counting or CPC), and then determines their concentration (by count). Aerosols include: sodium chloride, calcium carbonate, etc. This method is standard for determining respirator fit for users in healthcare settings and research laboratories.^{[20][21][22][23]}

Recently OSHA approved a Fast Fit Protocol which enables the AAC/CPC (Ambient Aerosol Concentration/Condensation Particle Counting) method to be performed in less than three minutes. The major advantage of the AAC/CPC method is that the test subject is moving and breathing while the fit factor is being measured. This better replicates the actual conditions the respirator will be used in.

Generated aerosol method

Flow (pressure) methods

Flow methods are a more recent development. When a worker inhales, some aerosol is deposited in their respiratory system, lowering the exhaled concentration. During inhalation leaked unfiltered air trickles under the mask, before mixing with air inside the mask. If such a stream collides with the sampling probe, the measured concentration becomes higher than the actual value. But if the trickle does not come into contact with a probe the concentration becomes lower.

Control Negative Pressure (CNP) directly measures the volume of air leaking into the respirator, and this is converted into a fit factor. Using a challenge pressure of 53.8 – 93.1 L/min, the CNP devices stress the mask as a user would while breathing heavily under extreme physical conditions. A CNP device manufacturer claims that using air as a standard challenge agent provides a more rigorous test of mask fit than an aerosol agent. If air leaks into a respirator then, particles, vapors, or gas contaminants may also leak in. Redon protocols allow a fit test to be performed in under 3 minutes.^{[citation needed]} The CNP Method of fit testing is OSHA, NFPA and ISO certified (among others).

Dichot method differs from CNP in that common filters are installed on the mask and air is quickly pumped out from the mask, creating a vacuum. The negative pressure depends on the filter resistance and leak rate. Filter resistance is measured with a sealed attachment of the mask to a dummy, allowing calculation of the leak rate through the gaps.

Industry

U.S. law began requiring employers assign and test a mask for each employee before assignment to positions requiring respirator use and thereafter every 12 months, and optionally, in case of circumstances that could affect fit (injury, tooth loss, etc.).^[18] Other countries have similar requirements.^[17][24] A U.S. study showed almost all large enterprises complied with these regulations. About half of enterprises with fewer than 10 workers were non-compliant in 2001.^[25] Such violations may be due to the cost of quantitative fit test equipment, qualitative fit test inaccuracy, and small organizations having fewer rigorous compliance processes.

Comparison

The main advantage of qualitative fit tests is low equipment cost, while their main drawback is their modest precision, and they are not sensitive enough for masks for atmospheres exceeding 10 PEL. To reduce the risk of choosing a poorly fitting respirator, the mask needs a sufficient fitting characteristic. Multiple masks must be examined to find the "most reliable", although poor test protocols may give incorrect results. Re-checks require time and increase costs. In 2001, the most common QLFT was irritant smoke and saccharin, but in 2004, NIOSH advised against using irritant smoke.

CNP is a relatively inexpensive and fast quantitative method.^[26] However, disposable filtering face-piece mask (such as the N95, N99, and N100 masks) cannot be tested with CNP. Fit tests with an atmospheric aerosol may be used on any respirator, but the cost of earlier devices (PortaCount) and the duration of the test was slightly greater than CNP. However the newer OSHA Fast Fit Protocols for CNC methods, and newer instruments, have made all quantitative fit test devices equivalent in price and speed. The CNP method has at present about 15% of the fit test market in industry.^[25] The Current CNC instruments are the PortaCount 8040 and the AccuFIT 9000.

User seal checks and respirator training should be done before fit testing.

Fit test methods for various masks^[15][27][28]

Fit test method	Respirator types			Devices for testing
	Filtering half facepiece	Elastomeric half facepiece respirators and elastomeric full facepiece mask, used in workplaces with concentrations of contaminants up to 10 PEL	Elastomeric full facepiece mask, used in workplaces with concentrations of contaminants up to 50 PEL
Qualititative fit test methods
Isoamyl acetate	Unlikely to pass[a]	Yes	No	Allegro-0202 et al.
Saccharin	Yes	Yes	No	3М FT-10 et al.
Bitrex	Yes	Yes	No	3М FT-30 et al.
Irritant smoke[b]	Class-100 filters only[28]	Yes	No	Allegro-2050, VeriFit, RAE 10-123-01 et al.
Quantitative fit test methods
Control Negative Pressure (CNP)[c]	Impossible to pass[d]	Yes	Yes	FitTester 3000 (DNI Nevada/OHD), Quantifit (OHD)
Ambient Aerosol method (CPC)	Yes	Yes	Yes	PortaCount, Accufit 9000
Generated Aerosol method (Aerosol Photometer)	Oil-resistant filters only[e]	Yes	Yes	TDA-99M, TSI 8587A

1. Although called 'Banana oil,' implying it could be used with oil resistant filters, the protocol requires organic vapor cartridges, according to the US Navy.^[28] Organic vapor cartridges are not found on filtering facepiece respirators.
2. Not recommended by NIOSH.^[29]
3. CNP with modeled breathing rate. The status of Quantafit (Dynatech Frontier) CNP modeled decay rate is unknown.^[30]
4. CNP machines cannot test respirators where the entire assembly is penetrable by air, like a filtering facepiece.
5. Generated aerosols use DOP or PAO as a test agent, similar to the oil used during initial respirator approval.^[28]