Respirator fit test

This painting by F.H. Varley 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 encountered in practice

The fitting characteristic of a respirator tight fitting face-piece is the ability of respirator's mask to separate a worker's respiratory system from polluted surrounding air. This is achieved through tightly pressing the mask flush against the face (without gaps) to ensure an efficient seal on the perimeter of their contact. Because the workers cannot be protected if there are gaps, it is necessary to test the efficiency of the mask before any employees enter into contaminated workplace air. Such gap, or leakage, search (fit test) may be performed in different ways.

History of the fit test

The effectiveness of various types of respirators was measured not only in the laboratories, but also in the workplaces.[1] These numerous measurements have shown that, in practice,the effectiveness of negative pressure tight fitting respiratory protective devices (RPD) depends on leakage between the mask and the face, not on the filters/canisters (if they are correctly chosen).[2] This decrease in efficiency due to leakage had manifested on a large scale during the first world war, when gas masks were used to protect against chemical weapons. If the soldiers wore masks improperly, or 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.[3][4] Such testing also helped to convince the soldiers that their gas masks were reliable - because respirators were a novelty.[5] 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),[6][7][8] and late[9]'. German firefighters used a similar test between the First and Second World Wars.[10] Diluted chloropicrin was used to test industrial gas masks, but not often.[11] The Soviet Army used chloropicrin in tents with a floor space of 16 square meters.[12]

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

Fit test in US Navy

Fit test methods

Currently, respirators are used to protect workers in developed countries, and their selection and use are regulated by national legislation.[13][14][15] These requirements include a 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.[13] This standard regulates the selection and organization of the use of respirators (Appendix A contains the 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 is correctly fitted to the employees’ face, they will be better protected in hazardous workplaces.[16]

Qualitative fit test methods (QLFT)

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

Irritant smoke fit test

Quantitative fit test methods (QNFT)

Using equipment to determine the concentrations of a 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.

An 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 a natural atmospheric. The ratio of external concentration to the concentration under the mask is called a fit factor (FF).[18] U.S. law requires the employer to offer employees a mask with enough large 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 faceipiece masks (used when the concentration of harmful substances is not more than 50 PEL), the fit factor should not be less than 500. The safety factor of 10 should compensate the difference between testing conditions and conditions in the workplace. To use an atmospheric aerosol one needs a 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 aerosols may be: sodium chloride, dioctyl phthalate, paraffin oil, and others.

These fit test methods appeared later than aerosol methods. They were developed to address the shortcomings of aerosol methods. 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 moves under the mask as a trickle, not actually mixing with air under the mask. If such a stream collides with the sampling probe, the measured concentration will be higher than the actual average concentration. But if the trickle will does not come into contact with a probe the 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. The CNP method is very accurate and fast, but it cannot be used to check filtering half face-piece respirators.

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

Dichot metod. This method differs from the CNP method 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 is a vacuum under the mask, and the 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 a tester to take into account the differences in the resistance of different filters, and the CNP method does not allow it.[19] 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 their 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 low sensitivity). To reduce the risk of erroneous use of a respirator with poor fit (which may cause damage to health) the mask needs to have a sufficiently high fitting characteristic. But this means that one must check out different masks to find the "most reliable" test, 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 increase costs for respiratory protection. In 2001, the most commonly used QLFT was irritant smoke and saccharin, but in 2004, the National Institute for Occupational Safety and Health (NIOSH) advised that fit tester stop using irritant smoke.

CNP is a relatively inexpensive, accurate and fast fit test method among quantitative methods (fit test devices: FitTester 3000, Quantifit).[20] However, it is not possible to fit test the filtering half of a face-piece mask with CNP. Artificial aerosol is almost never used to fit test respirators now. This is mainly 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 respirators, but the cost of the device and the duration of the test is greater than when using CNP. Therefore, the latter is used more often in industry (about 3 times as often).[21]

Respirator fit test in US Navy

Fit test in industry

U.S. law began to require the employer to conduct a respirator fit test for each employee prior to assignment to a position requiring the use of a respirator and 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.).[17] Other developed countries have similar requirements.[15][22] 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, it was broken by about half of employers in 2001.[21] 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 can operate without as high a level of industrial hygiene.

Table. The use of different fit test methods to test different respirators masks[13][23]
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.

References

  1. ↑ Кириллов, Владимир; Филин АС; Чиркин АВ (2014). "Обзор результатов производственных испытаний средств индивидуальной защиты органов дыхания (СИЗОД)". Toxicological Review (in Russian). Moscow: ФБУЗ "Российский регистр потенциально опасных химических и биологических веществ" Роспотребнадзора (6(129)): 44–49. doi:10.17686/sced_rusnauka_2014-1034. ISSN 0869-7922. Translation in English (in Wikisource): The Overview of Industrial Testing Outcome of Respiratory Organs Personal Protection Equipment
  2. ↑ Lenhart, Steven; Donald L. Campbell (1984). "Assigned protection factors for two respirator types based upon workplace performance testing". The Annals of Occupational Hygiene. BOHS, Oxford University Press. 28 (2): 173–182. doi:10.1093/annhyg/28.2.173. ISSN 1475-3162.
  3. ↑ Фигуровский, Николай (1942). Очерк развития русского противогаза во время империалистической войны 1914—1918 гг. (in Russian). Moscow, Leningrad: Издательство Академии наук СССР. p. 97.
  4. ↑ Болдырев, Василий (1917). Краткое практическое наставление к окуриванию войск (in Russian) (2 ed.). Moscow: Учеб.-фронтовый подотд. при Отд. противогазов В.З. и Г.С. p. 34.
  5. ↑ Чукаев К.И. (1917). Ядовитые газы (Наставление по противогазовому делу для инструкторов противогазовых команд, унтер-офицеров, а также для всех грамотных воинск. чинов) (in Russian). Kazan: типо-лит. Окр. штаба. p. 48.
  6. ↑ Митницкий, Михаил; Свикке Я.; Низкер С. (1937). В противогазах на производстве (in Russian). Moscow: ЦК Союза Осоавиахим СССР. p. 64.
  7. ↑ П. Кириллов, ed. (1935). Противогазные тренировки и камерные упражнения в атмосфере ОВ (in Russian). Moscow: Издание Центрального Совета ОСОАВИАХИМ СССР. p. 35.
  8. ↑ Достаточно ли ловок? // Новый горняк : Журнал. — Харьков, 1931. — В. 16
  9. ↑ Ковалев Н. (1944). Общие правила № 106 по уходу, хранению и работы в изолирующих, фильтрующих и шланговых промышленных противогазах, уход и работа на кислородном насосе (in Russian). Лысьва: Камский целлюлоз.-бум. комбинат. p. 106.
  10. ↑ Вассерман М. (1931). Дыхательные приборы в промышленности и в пожарном деле (in Russian). Moscow: Издательство Народного Комиссариата Внутренних Дел РСФСР. pp. 42, 207, 211, 221.
  11. ↑ Тарасов, Владимир; Кошелев, Владимир (2007). Просто о непростом в применении средств защиты органов дыхания (in Russian). Perm: Стиль-МГ. p. 279. ISBN 978-5-8131-0081-9.
  12. ↑ Чугасов АА (1966). "5 Проверка подбора лицевой части и исправности противогаза". Наставление по пользованию индивидуальными средствами защиты (in Russian). Moscow: Военное издательство Министерства обороны СССР. pp. 65–70.
  13. 1 2 3 US OSHA Standard 29 Code of Federal Register 1910.134 "Respiratory protection". Appendix A "Fit Testing Procedures"
  14. ↑ British Standard BS 4275-1997 "Guide to implementing an effective respiratory protective device programme"
  15. 1 2 DIN EN 529-2006. Respiratory protective devices - Recommendations for selection, use, care and maintenance - Guidance document; German version EN 529:2005
  16. ↑ Ziqing, Zhuang; Christopher C. Coffey; Paul A. Jensen; Donald L. Campbell; Robert B. Lawrence; Warren R. Myers (2003). "Correlation Between Quantitative Fit Factors and Workplace Protection Factors Measured in Actual Workplace Environments at a Steel Foundry". American Industrial Hygiene Association Journal. AIHA & ACGIH. 64 (6): 730–738. doi:10.1080/15428110308984867. ISSN 1542-8117.
  17. 1 2 Bollinger, Nancy; Schutz, Robert; et al. (1987). A Guide to Industrial Respiratory Protection. NIOSH-Issued Publications, DHHS (NIOSH) Publication No. 87-116. Cincinnati, OH: National Institute for Occupational Safety and Health.
  18. 1 2 Bollinger, Nancy; et al. (October 2004). NIOSH Respirator Selection Logic. NIOSH-Issued Publications, DHHS (NIOSH) Publication No. 2005-100. Cincinnati, OH: National Institute for Occupational Safety and Health.
  19. ↑ Krishnan, Usha; Arvydas Juozaitis; Matti Lehtimäkia; Krzysztof Szewczyka (1994). "Development of a Dichotomous-Flow Quantitative Fit Test for Half-Mask and Full-Facepiece Respirators". American Industrial Hygiene Association Journal. AIHA & ACGIH. 55 (5): 223–229. doi:10.1080/15428119491019069. ISSN 1542-8117.
  20. ↑ Crutchfield, Clifton; Richard W. Murphy; Mark D. Van Ert (1991). "A comparison of controlled negative pressure and aerosol quantitative respirator fit test systems by using fixed leaks". American Industrial Hygiene Association Journal. AIHA & ACGIH. 52 (6): 249–251. doi:10.1080/15298669191364677. ISSN 1542-8117.
  21. 1 2 U.S. Department of Labor, Bureau of Labor Statistics (2003). Respirator Usage in Private Sector Firms (PDF). Morgantown, WV: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. pp. 138–142.
  22. ↑ HSE 282/28 "FIT TESTING OF RESPIRATORY PROTECTIVE EQUIPMENT FACEPIECES"
  23. ↑ Charles Jeffress (1998). OSHA Instruction CPL 02-00-120 "Inspection procedures for the Respiratory Protection Standard" 09/25/1998 - VII. Inspection Guidelines for the Standard on Respiratory Protection - G. Fit Testing

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