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A respirator fit test checks whether a respirator properly fits the face of someone who wears it. The fitting characteristic of a respirator is the ability of the mask to separate a worker's respiratory system from ambient air.
Contents
- History
- Fit test methods
- Qualitative
- Quantitative
- Aerosol methods
- Flow pressure methods
- Comparison
- Industry
- References
This is achieved by tightly pressing the mask flush against the face (without gaps) to ensure an efficient seal on the mask perimeter. Because wearers cannot be protected if there are gaps, it is necessary to test the fit before entering into contaminated air. Multiple forms of the test exist.
Scientific studies have shown that if the mask size and shape is correctly fitted to the employees’ face, they will be better protected in hazardous workplaces.
History
The effectiveness of various types of respirators was measured in laboratories and in the workplace. 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. 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. Such testing helped convince the soldiers that their gas masks were reliable - because respirators were a novelty. Later, industrial workers were trained in gas chambers 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. The Soviet Army used chloropicrin in tents with a floor space of 16 square meters.
The US army provides military training using an irritating smoke.
Fit test methods
Respirator selection and use are regulated by national legislation in many countries. These requirements 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 Occupational Safety and Health Administration OSHA. This standard regulates respirator selection and organization (Appendix A describes fit testing). Compliance with this standard is mandatory for US employers.
Qualitative
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, making this test dependent on the subject reporting 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:
Quantitative
Equipment can determine the concentrations of a control substance inside and outside the mask or to determine the flow rate of air flowing under the mask. Quantitative methods are more accurate and reliable than qualitative methods.
Aerosol methods
An aerosol test is carried out by measuring the internal and external aerosol concentrations. The aerosol can be artificially created (to check the mask), or a natural atmospheric component. The ratio of external concentration to the concentration under the mask is called a fit factor (FF). U.S. law requires employers to offer employees a mask with large enough fit factor. For half face-piece masks (used when the concentration of harmful substances is not more than 10 PEL), the fit factor should not be less than 100; and for full face masks (not more than 50 PEL), the fit factor should not be less than 500. The safety factor of 10 compensates for the difference between testing and workplace conditions. To use an atmospheric aerosol one needs a PortaCount device. This device increases the size of the smallest particles due to vapor condensation and then determines their concentration (by count). Artificial aerosols may be: sodium chloride, dioctyl phthalate, paraffin oil and others.
Flow (pressure) methods
These methods appeared later than aerosol. They were developed to address the latter's shortcomings. When a worker inhales, a portion of the aerosol is deposited in their 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 trickles under the mask, not actually mixing with air under 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 air leakage volume. A worker wears the mask and holds his/her 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 remains constant (about 7 seconds). If the vacuum is constant, the amount of leaked air is equal to the volume of pumped air and the last value is accurately measured. The CNP method is very accurate and fast, but cannot be used to check filtering half face-piece respirators.
Dichot method differs from CNP in that common filters are installed on the mask and the air is pumped out from the mask at high speed, simulating a real breath. In this case, a vacuum exists under the mask. The degree of negative pressure depends on the resistance of the filters and on the amount of leaking air. The resistance of the filter is measured with a sealed attachment of the mask to a dummy. This allows the operator to determine the amount of air leaking through the gaps. This method allows the tester to consider the differences in the resistance of different filters, while the CNP method does not allow it. Dichot is not OSHA approved and is not included in the regulatory standard.
Comparison
The main advantage of qualitative fit test methods is the low cost of equipment, while their main drawback is their modest precision, and that they cannot be used to test tight-fitting respirators that are intended for use in atmospheres that exceed 10 PEL (due to the low sensitivity). To reduce the risk of choosing a respirator with poor fit, the mask needs to have a sufficiently high 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 commonly used QLFT was irritant smoke and saccharin, but in 2004, NIOSH advised against using irritant smoke.
CNP is a relatively inexpensive, accurate and fast method among quantitative methods. However, it is not possible to fit test the filtering half of a face-piece mask with CNP. Artificial aerosol fell out of favor due to the need to use an aerosol chamber or a special shelter that supports a given aerosol concentration which makes the test too difficult and costly. Fit tests with an atmospheric aerosol (PortaCount device) may be used on any respirator, but the cost of the device and the duration of the test is greater than CNP. Therefore, the latter is used 3 times as often in industry.
Industry
U.S. law began to require employers to assign and test a mask for each employee prior to assignment to a position requiring the use of a respirator and thereafter every 12 months, and optionally, in case of circumstances that could affect fit (injury, tooth loss, etc.). Other developed countries have similar requirements. A U.S. study showed that this requirement was fulfilled by almost all large enterprises. In small enterprises, with fewer than 10 workers, it was broken by about half of employers in 2001. The main reason for 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 have fewer rigorous compliance processes.
+ - may be used; - - cannot be used; (*) - NIOSH recommended to stop using this method.