Cartridges and canisters of air-purifying respirators

End of Service Life Indicator (ESLI). The saturation of the sorbent mercury vapor leads to the change of the color (circle in the center) from orange to brown

Employees working in a polluted atmosphere use respirators for health preservation. If the air in the workplace is polluted with noxious gases, but contains a lot of oxygen[1] they often use air-purifying respirators (APR). These respirators provide employees breathable air due to the cleaning of contaminated ambient air with gas canisters or cartridges. (Сanisters and cartridges are named "cartridges" in this text late - for brevity). There are cartridges of different types, and they must be chosen correctly, and replaced in time.

The principles of purification of polluted air in APR

Absorption

Capture noxious gases may be accomplished by the sorbents.[2] These materials (activated carbon, aluminium oxide etc.) have a large specific surface area and can absorb gases. Typically, such sorbents used in the form of granules, and cartridge case is filled with them. Contaminated air travels through the bed of sorbent granules in the cartridge, and movable harmful gas molecules collide with the surface of the sorbent, and remain therein. The sorbent is saturated the molecules caught, and gradually loses its ability to capture the gases. So, contaminated air can pass through the saturated sorbent to the layers of fresh sorbent. The concentration of harmful substances in the purified air after prolonged use of the cartridge increases, and may exceed the Permissible Exposure Limit PEL. Therefore, the service life of the cartridges is limited. The bond strength between the captured molecule and sorbent has a small, and the molecule is able to separate from the sorbent and get into the air again. The ability of the sorbent to capture the gases depends on: the properties of the gases and their concentrations, the air temperature, the air relative humidity, the rate of air consumed by the employee, and many other factors. Activated carbon can be saturated with chemicals that make more stronger ties with molecules of trapped gases - to improve the capture of a number of harmful gases. The saturation of the activated carbon with iodine - improves the capture of mercury; saturation of metal salts - improves the capture of ammonia; saturation metal oxides - improves capture acid gases.[3]

The chemical reaction between the gas and the absorber (chemisorption)

The ability of some harmful gases to react chemically with some other substances can be used to capture them. For example, the authors[2] describe the ability of copper salts to form complex compounds with ammonia. Creating strong links between the gas molecules and the sorbent may allow one to use of gas canisters repeatedly - if it has sufficient unsaturated sorbent.

The catalytic decomposition

Some harmful gases can be neutralized through catalytic oxidation. A hopcalite can oxidize toxic carbon monoxide, CO to harmless carbon dioxide. But the effectiveness of this catalyst strongly decreases with relative humidity increases. Therefore, there are some drier (desiccant) in the canisters (before such catalysts). A polluted air always contains water vapor, and after the saturation of the desiccant - catalyst ceases carbon monoxide neutralization.

Combined cartridges

If employer use combined (multigas) cartridges, that provide air purification from a combination of different harmful gases, they apply gas cartridges with such sorbents or/and catalysts, that is necessary to capture the gases; and such canister are subject to all relevant constraints.

Classification and marking of cartridges

United States

In the U.S., manufacturers can certify cartridges intended for purifying workplace air from various gaseous contaminants.[4]

The orange color can be used for painting the entire cartridge housing, or as a strip. But this color is not in the table, and to determine from what protects the cartridge with such color one should read the inscription.

The legislation requires the employer to select cartridges using only labels and not the color of the markings (to reduce the risk of error).

European Union and RF

In the EU and in RF,[6][7][8][9][10] manufacturers can certify cartridges intended for cleaning air of various gaseous contaminants.

Cartridges AX, SX and NOP3 not distinguish on the sorption capacity (as in the US) when they are classified and certified.

If the cartridge is designed to protect from several different types of harmful gases, in the designation contains the list of designations for specific types of perceived harmful gases, for example: A2B1, color - brown and grey.

Choice and timely replacement of cartridges

Selection of cartridge should be carried out after determining the composition of the atmosphere in the workplace. To choose the right types of cartridges in the U.S., the employer may use the NIOSH guide[11] or the recommendations of the manufacturers. The service life of all types of cartridges is limited. Therefore, the employer is obliged to replace them in a timely manner.

The use of subjective reactions of an employee’s sensory system

The use of cartridges in the contaminated atmosphere leads to saturation of the sorbent (or the dryer — when using catalysts). The concentration of harmful gases in the purified air gradually increases. The ingress of harmful gases in the inhaled air can lead to the reaction of the employee’s sensory system: odor, taste, irritation of the respiratory system, dizziness, headaches, and other health impairments (up to loss of consciousness).[12]

These signs (known in the U.S. as "warning properties" - p. 28[12]) indicate that one must leave the polluted workplace area, and replace the cartridges with a new one. (This can also be a symptom of a loose fit the mask to one face and the leakage of unfiltered air through the gaps between the mask and the face). Historically, this method is the oldest.

The advantages of this method – if harmful gases have warning properties at concentrations less than 1 PEL, the replacement will be produced in a timely manner (in most cases, at least); the application of this method does not require the use of special cartridges (more expensive) and accessories; replacement happens when one need to do it – after the sorbent saturation, and without any calculations; the sorption capacity of the cartridges is fully expired (which reduces costs for respiratory protection).

The disadvantage of this method is that some of harmful gases have no warning properties. For example, there is a list of more than 500 harmful gases in the[13] and more than 60 of them have no warning properties, and there are no any such information for more than one hundred of them. So, if one uses warning properties to replace cartridges, this leads to breathiing air with excess harmful gas concentration in some cases. The table contains a list of the chemicals that have no warning properties.

If the threshold odor of pentaborane is 194 PEL; and if it concentration is only 10 PEL, one cannot timely change cartridges with using smell - they could be "used" forever (bur they cannot protect forever).

Practice has shown that the presence of warning properties not always leads to the timely replacement of cartridges.[14] A study[15] showed that on average 95% of a group of people has an individual threshold of olfactory sensitivity in the range of from 1/16 to 16 from the mean. This means that 2.5% of people will not be able to smell harmful gases at a concentration 16 times greater than the average threshold of perception of a smell. The threshold of sensitivity of different people can vary by two orders of magnitude. That is, 15% of people do not smell at concentrations 4 times higher sensitivity threshold. The value of threshold smell greatly depends on how much attention people pay this, and on their health status.

Modern methods of determining the necessity of cartridges replacement

Cartridges certification provides a minimum value of their sorption capacity. US OSHA standard for 1,3-Butadiene indicates the specific service life of the cartridges.[16]

Computer programs for calculating the service life of the cartridge

The world's leading manufacturers of respirators offered its customers a computer program for calculating the service life already in the 2000.

3M program[20] allowed to calculate the service life of the cartridges exposed with more than 900 harmful gases and their combinations (in 2013). The MSA program[21] allow to take into account hundreds of gases and their combinations. Same program was developed by Scott[24] and Dragerwerk.[25] J. Wood developed a mathematical model and software which now allows one to calculate the service life of any cartridges with known properties.[26][27] Now OSHA uses it in program Advisor Genius.[28]

This file is the scheme of installation of the cartridge with End of Service Life Indicator (ESLI) on a half-mask respirator, so that the ESLI is visible during operation. The color change shows that the cartridges will cease to capture ammonia, and the employee should leave the workplace to replace the cartridges

The merit of this way of replacing the cartridges is that it allows an employers to use normal, "common" cartridges, and if they have the exact data, they may replace them in time. The downside is that because of air contamination is often not constant, and the nature of the work to be performed is not always stable (that is, the flow of air through the cartridges is not permanent), it is recommended to use working conditions for calculations, equal to the worst (for reliable protection of workers). But in all other cases cartridges will be replaced with partially used sorbent. This increases the costs of respiratory protection due to more frequent cartridges replacement.

End of Service Life Indicators (ESLI)

If the cartridges have a device that warns of an employee of the approaching expiration of the term of service life (End of Service Life Indicators, ESLI), the signals of such devices can be used for the timely replacement of cartridges. ESLI can be active[29] or passive.[30] Passive indicators often use sensor that changes color. This element is installed in the cartridge at some distance from the filtered air outlet (to color change occurred before the harmful gases begin to pass through the cartridge). An active indicators is use signal from sensor to emit a light signal (or turn on a sound alarm) to inform an employee that he or she must left the contaminated atmosphere and changed the cartridge.

Active indicators used light or audible alarm for employee notification that is triggered by a sensor, that is usually installed in cartridge. Such indicators allow one to replace the cartridges on time in any light, and do not require the worker to pay attention to the color of the indicator. They can also be used by workers who badly distinguish different colors.

Despite the presence of solutions for technical problems, and the availability of the established certification requirements to the ESLI,[31] during the period from 1984 (first certification standard with requirements for active ESLI) until 2013 nor one cartridge with active ESLI was approved in the US. It turned out that the requirements for the cartridges are not quite exact, and requirements for employers are under no obligation to use these indicators quite specifically. Therefore, respirators’ manufacturers fear of commercial failure when selling a new unusual products - although they continue to carry out research and development work in this area.

But examination of the use of respirators showed that in the U.S. more than 200 thousand workers may be exposed to excessive harmful gases due to the late replacement of cartridges.[32] So, Laboratory of PPE (NPPTL) at the NIOSH began to develop an active ESLI. After the completion of the work, by its results, the legal requirements will be clarified, the requirements of the employer will be formulated, and the resulting technology will be transferred to industry - for use in new improved RPD.

Reusing cartridges

If the cartridge contains a lot of the sorbent and if the concentration of contaminants is low; or if the cartridge was used for a short duration of time, after completion of its use, it still has a lot not saturated sorbent (which can capture gases). This may allow use such cartridges again.

The molecules of an entrapped gases may de-absorb during storage of the cartridge. Due to the difference of concentrations inside the body of the cartridge (at the inlet concentration is greater; at the outlet for purified air concentration is lesser), these de-absorbed molecules migrate inside the cartridge to the outlet. The study of cartridges exposed to methyl bromide showed that this migration can impede the re-use after storage.[33] The concentration of harmful substances in the purified air may exceed the PEL (even if clean air is pumped through the cartridge). To protect workers ' health, U.S. law does not allow reuse cartridges, when exposed to harmful substances, which are able to migrate (even if the cartridge has many non-saturated sorbent after the first use). According to the standards, "volatile" substances (able to migrate) are considered a substances with a boiling point below 65 °C. But studies have shown that at the boiling point above 65 °C the reuse of the cartridge may be unsafe. Therefore, the manufacturer must provide the buyer with all information required for the safe use of cartridges. So, if the period of continuous service life of the cartridge (calculated by the program - see above) exceeds 8 hours (tables 4 and 5), the legislation may limit their use to one shift.

The paper [34] provides a procedure for calculating the concentration of harmful substances in purified air at the start of the re-use of cartridges (which allows one to determine exactly where they may be safe reused). But these scientific results are not yet reflected in any standards or guidelines on the use of respirators. It is interesting to note that the author of the article, working in the US, did not even try to consider the use of gas cartridges for the third time (or more). On the website of the author one can download for free a computer program that allows one to calculate the concentration of harmful substances immediately after the start of re-use of the cartridge (which allows one to determine if this is safe).[27]

The legal requirements for the timely replacement of respirator’s cartridges

Promising full facepiece respirator equipped with (ESLI)[35]

Since it is not always possible to replace cartridges in a timely manner through the use of their odor ets, OSHA has banned the use of this method. The employer is obliged to use only two ways to replace cartridges:[36] on schedule, and by using ESLI (because only these methods provide reliable preservation of workers’ health). Instructions to inspectors (OSHA) provides specific guidance on inspection of implementation of such requirements.[37] On the other hand, the state requires manufacturers to provide the consumer with all the necessary information about cartridges, that allows one to make schedule for replace them timely. Similar requirements exist in the standard on occupational safety, governing the selection and application of RPD in EU.[38] In England a tutorial on the selection and use of respirators recommends obtain information from the manufacturer, and replace the cartridges on a schedule, or use ESLI, and prohibits reuse cartridges after exposure of volatile substances that can migrate.[39]

References

  1. ↑ (>19.5% in US; >18% in RF)
  2. 1 2 Дубинин, Михаил; Чмутов К. (1939). Физико-химические основы противогазного дела (in Russian). Moscow: Военная академия химической защиты имени К.Е. Ворошилова.
  3. ↑ Clayton G.D.; Clayton E.F (1985). Patty's Industrial Hygiene and Toxicology 1 (3 ed.). New York: Willey-Interscience. p. 1008. ISBN 0-471-01280-7.
  4. ↑ 42 Code of Federal Register 84 Approval of respiratory protective devices §84.113 — Canisters and cartridges; color and markings; requirements
  5. ↑ Rosenstock, Linda; et al. (1999). "Appendix A". TB Respiratory Protection Program In Health Care Facilities. DHHS (NIOSH) Publication No. 99-143. Cincinnati, Ohio: National Institute for Occupational Safety and Health. pp. 42–44.
  6. ↑ ГОСТ Р 12.4.193-99 Occupational safety standards system. Respiratory protective devices. Gas filters and combined filters. General specifications (on Russian)
  7. ↑ ГОСТ Р 12.4.231-2007 Occupational safety standards system. Respiratory protective devices. АX gas filters and combined filters for protection against low-boiling organic compounds. General specifications (on Russian)
  8. ↑ ГОСТ Р 12.4.232-2007 Occupational safety standards system. Respiratory protective devices. SX gas filters and combined filters for protection against specific named compounds. General specifications (on Russian)
  9. ↑ ГОСТ 12.4.235-2012 (EN 14387:2008) Occupational safety standards system. Respiratory protective devices. Gas filters and combined filters. General technical requirements. Test methods. Marking (on Russian)
  10. ↑ ГОСТ 12.4.245-2013 Occupational safety standards system. Respiratory protective devices. Gas filters and combined filters. General specifications (on Russian)
  11. ↑ Michael E. Barsan, ed. (2007). NIOSH Pocket guide to chemical hazards. DHHS (NIOSH) Publication No. 2005-149 (3 ed.). Cincinnati, Ohio: National Institute for Occupational Safety and Health. pp. xiv–xvi; xx–xxiii; 2–340.
  12. 1 2 Bollinger, Nancy; et al. (October 2004). NIOSH Respirator Selection Logic. NIOSH-Issued Publications. Cincinnati, OH: National Institute for Occupational Safety and Health.
  13. ↑ 2008 Respirator Selection Guide. St. Paul, MN: 3M. 2008. pp. 15–96.
  14. ↑ Myers, Warren; et al. (1987). "Appendice C. Odor warning: Background information.". In Donald Miller. NIOSH Respirator Decision Logic. DHHS (NIOSH) Publication No. 87-108. Cincinnati, Ohio: National Institute for Occupational Safety and Health. pp. 48–50.
  15. ↑ Amoore, John; Hautala Earl (1983). "Odor as an aid to chemical safety: odor thresholds compared with threshold limit values and volatilities for 214 industrial chemicals in air and water dilution". Journal of Applied Toxicology (John Wiley & Sons, Ltd) 3 (6): 272–290. doi:10.1002/jat.2550030603. ISSN 1099-1263.
  16. ↑ US OSHA occupational health and safety standard 29 Code of Federal Register 1910.1051 1,3-Butadiene 1910.1051(h)(3) Respirator selection
  17. ↑ ZieglerG., Martin; Hauthal W.; Koser H. (2003). Entwicklung von Indikatoren zur Anzeige des Gebrauchsdauer-Endes von Gasfiltern (Machbarkeitsstudie). Forschung Fb 997 (in German) (1 ed.). Bremerhaven: Wirtschaftsverl. ISBN 3-86509-041-9.
  18. ↑ Cothran T. (2000). "Features - Service Life Software for Organic Vapour Cartriges". Occupational Health and Safety (Waco, Tex.) 69 (5): 84–93. ISSN 0362-4064.
  19. ↑ The link to the document describing the program MerlinTM. Unfortunately, the product could not be found.
  20. 1 2 3M Service Life Software Version: 3.3 until January 1, 2016.
  21. 1 2 MSA program Cartridge Life Calculator link 1 link 2 (for US)
  22. ↑ Old link: Program for Cartridge Service Life calculation ezGuide
  23. ↑ Link to the manufacturer's website where You can download a program to calculate the life of the cartridges: S-Series - Software Downloads and T-Series - Software Downloads.
  24. ↑ The program for calculation of service life of respirator cartridges, developed by Scott: SureLife™ Cartridge Calculator
  25. ↑ Link to a database VOICE developed by Drager (version for US) with the program for calculation cartridge service life End-of-ServiceLife Calculator
  26. ↑ Wood, Gerry; Jay Snyder (2007). "Estimating Service Lives of Organic Vapor Cartridges III: Multiple Vapors at All Humidities". Journal of Occupational and Environmental Hygiene (AIHA & ACGIH) 4 (5): 363–374. doi:10.1080/15459620701277468. ISSN 1545-9632.
  27. 1 2 Computer program "MultiVapor with IBUR" - Immediate Breakthrough Upon Reuse
  28. ↑ The program for calculation of service life of respirator cartridges that use a mathematical model of Jerry Wood: Advisor Genius
  29. ↑ Rose-Pehrsson, Susan L.; Williams, Monica L. (2005). Integration of Sensor Technologies into Respirator Vapor Cartridges as End-of-Service-Life Indicators: Literature and Manufacturer's Review and Research Roadmap. Washington, DC: US Naval Research Laboratory. p. 37.
  30. ↑ Favas, George (July 2005). End of Service Life Indicator (ESLI) for Respirator Cartridges. Part I: Literature Review (PDF). Victoria 3207 Australia: Human Protection & Performance Division, Defence Science and Technology Organisation. p. 49.
  31. ↑ US NIOSH occupational safety and health standard 42 Code of Federal Register 84 Approval of Respiratory Protective Devices ‘’84.255 Requirements for end-of-service-life indicator.‘’
  32. ↑ 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. 214 (table 91).
  33. ↑ Maggs, F. A. P.; Smith, M. E. (1975). "The Use and Regeneration of Type-O Canisters for Protection Against Methyl Bromide". Annals of Occupational Hygiene 18 (2): 111–119. doi:10.1093/annhyg/18.2.111. ISSN 0003-4878.
  34. ↑ Wood, Gerry O.; Snyder, Jay L. (2011). "Estimating Reusability of Organic Air-Purifying Respirator Cartridges". Journal of Occupational and Environmental Hygiene 8 (10): 609–617. doi:10.1080/15459624.2011.606536. ISSN 1545-9624.
  35. ↑ NPPTL presentation (2007) Sensor Development for ESLI & Application to Chemical Detection
  36. 1 2 US OSHA occupational safety and health standard 29 Code of Federal Register 1910.134 Respiratory Protection
  37. ↑ Charles Jeffress (OSHA) Instruction CPL 2-0.120 (1998)
  38. ↑ EN 529-2005 Respiratory protective devices - Recommendations for selection, use, care and maintenance - Guidance document
  39. ↑ HSE (2013). Respiratory protective equipment at work. A practical guide (PDF) (4 ed.). Health and Safety Executive. ISBN 978 0 7176 6454 2.
  40. ↑ Bollinger, Nancy; Schutz, Robert; et al. (1987). A Guide to Industrial Respiratory Protection. NIOSH-Issued Publications. Cincinnati, OH: National Institute for Occupational Safety and Health.
  41. ↑ BS 4275:1997 Guide to implementing an effective respiratory protective device programme
  42. ↑ DIN EN 529:2006. Atemschutzgerate - Empfehlungen fur Auswahl, Einsatz, Pflege und Instandhaltung.
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