Respirator fit test

The fitting characteristic of a respirator tight fitting facepieces is the ability of respirator's mask separate worker's respiratory system from polluted surrounding air. This is achieved through tight touch (without gaps) the mask and the face around the perimeter of their contact. Because the workers cannot be protected if there are gaps, it is necessary to find it before employee enter into contaminated workplace air. Such gap (or leakage) search (fit test) may be performed by different ways.

This painting by F.H. Varley, a future member of the Group of Seven, depicts a training exercise in Seaford, England. Soldiers emerge from a gas hut wearing respirators attached. Similar training was conducted under conditions that are getting closer to those that may be encountered in practice

History of fit test

The effectiveness of various types of respirators was measured not only in the laboratories, but also in the workplaces. These numerous measurements have shown that, in practice, negative pressure tight fitting respiratory protective devices (RPD) effectiveness depend on leakage between the mask and the face, not on the filters/canisters (if they are correctly chosen). This decrease in efficiency due to leakage had manifested on a large scale during the first world war, when the gas masks were used to protect against chemical weapons. If the soldiers wore masks sloppy, and if the mask didn't fit their faces, people could die. The Russian army began to use short-term exposure to chlorine at low concentrations to solve this problem in 1917. Such testing also helped to convince the soldiers that their gas masks are reliable - because respirators were a novelty. Later, industrial workers were trained in the gas chambers under the influence of harmful substances in the USSR (in preparation for the Second World War), and late'. German firefighters used a similar test between the first and second world wars. Diluted chloropicrin was used to test industrial gas masks, but not often. The Soviet Army used chloropicrin in tents floor space of 16 square meters.

Now the US army carried out military training with a special irritating smoke.

File:US Navy 061220-N-8146B-001 The Safety Department uses a plastic bag to conduct respirator fit testing aboard the amphibious assault ship USS Boxer (LHD 4).jpg

Fit test in US Navy

Fit test methods

Currently, respirators are used to protect workers in the developed countries, and their selection and use are regulated by national legislation. These requirements include fit test of negative pressure respirator’s mask for each worker - individually.

There are qualitative and quantitative fit test methods (QLFT & QNFT). Detailed description of fit test methods is given in the US standard, developed by Occupational Safety and Health Administration OSHA. This standard regulating the selection and organization of the use of respirators (Appendix A contain description of fit testing). The implementation of the requirements of this standard is mandatory for the employer.

Scientific studies have shown that if the mask size and shape better fit to the employees’ face, they will be better protected in the harmful workplaces.

Qualitative fit test methods (QLFT)

These methods use the reaction of workers to the taste or smell of a special material (if it leakage into mask in large degree) - gas, vapors or aerosols, and it help to detect the presence of gaps. Such reaction is subjective, and it depends on the work reporting results honestly. A qualitative fit test will start with an unfiltered/non-respirator sampling of the mist of choice to verify that the subject can detect the substance of choice. Experts use different types of substances to accomplish the fit testing.

• Isoamyl acetate. This substance has the smell of bananas. Since vapor can freely penetrate through the surface of the filtering half facepiece respirators, isoamyl acetate is used only for fit testing of elastomeric masks.
• Saccharin. An aerosol of an aqueous solution of saccharin (Sodium saccharin) is used to fit test both an elastomeric and filtering respirator masks. Saccharin is perceived as sweet taste. The employee should breathe through the mouth, slightly sticking out his tongue. The aerosol is created using a simple aerosol generator with rubber "pear", which is compressed manually.
• Bitrex. A substance with a bitter taste (Bitrex™) used to detect gaps. It is mixed with water and sprayed in the same manner as the above materials.
  File:US Navy 110429-N-7326M-028 Boatswain's Mate 3rd Class Shaka K. Farrier dons a respirator as irritant smoke is released into the air as part of a re.jpg

  Irritant smoke fit test
• Irritant smoke. An irritating smoke used to fit test respirators. It causes irritation of the mucous membranes — resulting in discomfort, coughing, sneezing, etc. NIOSH recommended discontinuing usage of this method because research has shown that exposure of this 'smoke' on the subject may significantly exceed Permissible exposure limit (PEL) (for example — if there are high humidity in the room).

Quantitative fit test methods (QNFT)

Using an equipment to determine the concentrations of control substance under the mask and outside the mask, or to determine the flow rate of air flowing under the mask through the gap(s), allows the operator to fit test the mask quantitatively. It is believed that these quantitative methods are more accurate and reliable than qualitative methods.

• Aerosol methods

Aerosol fit test is carried out by measurements of aerosol concentration under the mask and outside it, and the calculation of the ratio of these concentrations. The aerosol can be artificially created (to check the mask), or natural atmospheric. The ratio of external concentration to the concentration under the mask is called a fit factor (FF). U.S. law requires the employer to offer employees a mask with enough large fit factor. For half facepiece masks (used when the concentration of harmful substances is not more than 10 PEL), the fit factor shall be not less than 100; and for full-facepiece masks (used when the concentration of harmful substances is not more than 50 PEL), the fit factor shall be not less than 500. The safety factor of 10 should compensate the difference in conditions of such measurement and conditions in the workplace. To use atmospheric aerosol one need PortaCount device. This device increases the size of the smallest particles due to condensation of a vapor on them, and then determines their concentration (by count). Artificial aerosol may be: sodium chloride, dioctyl phthalate, paraffin oil, and others.

• Flow (pressure) methods

These fit test methods appeared later than aerosol methods. They were developed to address the shortcomings of aerosol methods. When worker inhale, a portion of the aerosol deposited in his respiratory organs, and the concentration measured during the inhalation becomes lower than during inhalation. It is important to note that during inhalation leaked unfiltered air moves under the mask as a trickle, not actually mixing with air under the mask. If such a stream will collide with the sampling probe, the measured concentration will be higher than the actual average concentration. But if the trickle will not face a probe concentration will be lower than the real average.

Control Negative Pressure (CNP) method uses direct measurement of the volume of air that leaked through the gaps. A worker put on his mask and holds his breath for ~10 seconds. The mask has a special fixture instead of filters - so that no air can pass beneath the mask. A measuring device pumps out air from the mask to create a vacuum (about 2 seconds). Then the device pumps out the air so that the vacuum remained constant (about 7 seconds). If vacuum is constant, the amount of leaked air is equal to the volume of pumped air, and the last value is accurately measured. Method CNP is very accurate and fast, but it cannot be used to check filtering half facepiece respirators.

File:Количественная проверка изолирующих свойств QLFT прибором PortaCount Plus.jpg

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

Dichot metod. This method differs from the method of CNP by the fact that at the time of measurement there are common filters on the mask, and the air is pumped out from the mask at high speed, simulating a real breath. In this case, there are vacuum under the mask, and degree of negative pressure depends on the resistance of the filters, and on the amount of air leaking under the mask through the gaps. The resistance of the filter is measured with a sealed attachment of the mask to the dummy, and this allows the operator to determine the amount of air leaking through the gaps. Dichot Method allows to take into account the differences in the resistance of different filters, and CNP method does not allow it. But Dichot is not OSHA approved, and it is not included in the standard on respiratory protection.

Advantages and disadvantages of different fit test methods

The main advantage of qualitative fit test methods is the extremely low cost of equipment, but their main drawback is a moderate precision, and that they cannot be used to fit test tight-fitting respirators that are intended for use in atmospheres which exceed 10 PEL (due to the small sensitivity). To reduce the risk of erroneous use of a respirator with poor fit (this may cause damage to health) the mask shall have a sufficiently high fitting characteristic. But this leads to the fact that one must check out different masks to find the "most reliable", although in many cases "not sufficiently reliable" masks were recognized as such by mistake (because of insufficient accuracy of ONFT or OLFT tests). Re-checks require time and it increase costs for respiratory protection. In 2001, the most commonly used QLFT is irritant smoke and saccharin. But in 2004, National Institute for Occupational Safety and Health (NIOSH) advised to stop using irritant smoke.

CNP is relatively inexpensive, accurate and fast fit test method among quantitative methods (fit test devices: FitTester 3000, Quantifit). But it is not possible to fit test the filtering half facepiece mask with CNP. Artificial aerosol is almost never used to fit test respirators now. This is mainly due to the need to use aerosol chamber or a special shelter that supports a given aerosol concentration - it is too difficult and costly. Fit test with an atmospheric aerosol (PortaCount device) may be used to any respirators; but the cost of the device and the duration of the test is higher than when using the CNP. Therefore, the latter is used more often in industry (about 3 times).

File:US Navy 040128-N-8955H-003 Damage Controlman 3rd Class James Allen from Oakland, Calif., conducts a MCU-2P Gas Mask fit test using a TDA 99M respirator functional testing system on Disbursing Clerk Seaman Recruit Aidan Lee.jpg

Respirator fit test in US Navy

Fit test in industry

U.S. law began to require the employer to conduct a respirator fit test each employee prior to assignment to a position requiring the use of a respirator; thereafter periodically every 12 months; and optionally, in case of any circumstances that may affect fit (change the shape of the face due to injury, tooth loss, etc.). Other developed countries have similar requirements too. The US study showed that this requirement was fulfilled by almost all large enterprises; but for small enterprises, where the number of workers does not exceed 10 people, in 2001 it was broken about half of employers. The main reason of such violations may be the high cost of specialized equipment for quantitative fit tests, insufficient accuracy of qualitative fit tests, and the fact that small organizations can operate without as high a level of industrial hygiene.

Table. The use of different fit test methods to test different respirators masks

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
Isoamil acetate	-	+	-
Saccharin	+	+	-	3М FT-10 et al.
Bitrex	+	+	-	3М FT-30 et al.
Irritated smoke (*)	-	+	-
Quantitative fit test methods
Control Negative Pressure CNP	-	+	+	Quantifit, FitTest 3000 (OHD)
Aerosol method	+	+	+	PortaCount et al.

+ - may be used; - - cannot be used; (*) - NIOSH recommended to stop using this method.

External links

• Respirator fit testing in YouTube