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Solving the canister conundrum: if it isn't authorized for the M40 series protective mask, don't use it!


The M40 series protective mask is a remarkable piece of equipment. It provides face, eye, and respiratory protection in chemical, biological, radiological, and nuclear environments; and it can be worn continuously for 8 to 12 hours. (1) The M40 series replaced the M17 series protective mask as the standard Army field mask in the early 1990s, and it is still produced for field and combat vehicle applications.

The M40A1 mask, which is specifically designed for field application, features a flexible, silicone facepiece with binocular, hard-coated, polycarbonate lenses with protective outserts; air inlet and outlet valves; front and side voicemitters; an internal/external drink tube system that interfaces with standard Army water canteens; and a "second skin" to provide protection against liquid contamination. Designed for combat vehicle application, the M42A2 mask has the same basic features as the M40A1 mask--plus a quick-doff hood, detachable microphone, and hose-and-canister carrier that allows the filter canister to be worn on the belt.

Filtration for the M40 series masks is provided by the C2A1 filter canister, which is a two-stage gas and particulate filter equipped with standard North Atlantic Treaty Organization threads. In the first stage, a pleated, high-efficiency particulate paper filters out airborne particles such as biological agents and dust. In the second stage, a bed of activated carbon impregnated with copper, silver, zinc, molybdenum, and triethylenediamine (commonly referred to as ASZM-TEDA) adsorbs chemical aerosols and gases. The C2A1 canister provides protection against a variety of chemical warfare agents (CWAs) including nerve, choking, blister, and blood agents. After passing through the C2A1 canister, filtered air is drawn through air inlet valves into the mask facepiece and nose cup and exhaled through a covered outlet valve assembly. (2)

The M40 series mask facepiece is manufactured in three sizes to fit the 5th to 95th percentile of Soldiers, and it features an inturned peripheral seal to provide a more secure fit. (3) The facepiece and mask accessories (including the filter canister, outserts, the waterproof bag, and the operator's manual) are contained in a rugged, canvas carry bag.

The M40 series masks have been standard issue for more than 20 years, and they have served our warfighters well. But as they reach the end of their effective service life, fielding is underway for the next generation of protective masks--primarily the Joint Service General-Purpose Mask. The Joint Service General-Purpose Mask will offer enhancements in chemical-biological protection (with dual filter elements) and performance (with improved vision, reduced breathing resistance, and increased comfort), which will reduce the physiological and psychological burdens normally associated with wearing protective masks.

The protective mask is designated as a "critical safety item" among the equipment the warfighter wears and carries. In the event of an attack involving a chemical or biological agent, a warfighter's protective mask can mean the difference between life and death. Because day-to-day operations can be hard on equipment, routine inspections and maintenance of the protective mask are essential in ensuring that the mask is ready when needed.

Problem Revealed

When units return from combat deployment, their equipment is assessed and restored to serviceable condition to ensure combat readiness for future missions. Special field support teams conduct reset operations on virtually every piece of unit equipment, including protective masks.

Only two types of filter canisters are currently authorized for military use with the M40 series masks--the aforementioned C2A1 (National Stock Number [NSN] 4240-01-361-1319) and the C2 (NSN 4240-01-119-2315). (Although C2 canisters continue to be authorized, they are no longer manufactured. Remaining C2 canisters have expired shelf lives and are no longer serviceable; therefore, they should be replaced as soon as possible.) However, during reset operations conducted within the past 2 years, it was discovered that units returning from Iraq and Afghanistan were turning in M40 series masks that contained unauthorized commercial filter canisters (for example, the 3M[TM] FR-C2A1 Filter Cartridge (4)).


The use of unauthorized commercial filter canisters with the M40 series masks is a troubling revelation. While the source of supply is unknown, it would not be difficult to purchase unauthorized canisters from sources outside the military supply system via the Internet or other electronic means. Although the unauthorized canisters are very similar in appearance to the authorized ones--and they have compatible North Atlantic Treaty Organization standard 40-millimeter threads--military and commercial canisters are designed and tested to meet different standards of protection against traditional CWAs and toxic industrial chemicals (TICs). These differences in standards are described in terms of the chemical threat, protection requirements, and filter change-out criteria.

Chemical Threat

The protection afforded by the canisters is dependent upon the chemical threat encountered. As a general rule, military protective masks are primarily designed to protect against battlefield concentrations of traditional CWAs and military chemical compounds. CWAs refer to the toxic chemicals--and their precursors--that are prohibited under the Convention on the Prohibition of the Development, Production, Stockpiling, and Use of Chemical Weapons and on their Destruction (commonly referred to as the "Chemical Weapons Convention"). (5) They are classified based on their physiological actions. Well-known CWAs include choking, nerve, blood, blister, and incapacitating agents. (6) Although military chemical compounds (which are classified as smoke/ obscurants, lacrimators [tearing agents], or respiratory irritants) are considered less toxic than CWAs, unprotected exposure to military chemical compounds can also have adverse effects.

Military chemical compounds include o-chlorobenzylidene malononitrile (commonly known as tear gas) and capsaicin (commonly known as pepper spray). (7) Although decontaminating agents (supertropical bleach, decontamination solution 2) are not classified as military chemical compounds, they are considered military-unique chemicals that can also have adverse effects in cases of unprotected exposure.

In contrast, commercial respirators and canisters are designed to protect against occupational and first responder exposures to TICs. TICs are toxic to humans, animals, and plants and are used in manufacturing processes, agriculture (pesticides), water treatment (chlorine), and other areas. They are characterized by their toxicity, corrosiveness, flammability, explosiveness, reactivity, chemical by-products, and quantity/ availability. The list of TICs is extensive and includes some compounds that are also classified as traditional CWAs, such as phosgene. (8)

The chemical threat posed by military and nonmilitary chemicals is a function of the duration of effectiveness, potency, and physiological action. Factors affecting the duration of effectiveness include the method of dissemination (vapor, aerosol, liquid), weather/terrain conditions (temperature, wind, humidity, topography, vegetation), physical properties (vapor pressure, freezing and melting points), and chemical properties (stability, reactivity). Factors affecting the potency and physiological action include the toxicity of the compound, the concentration/dosage, the route of exposure (inhalation, percutaneous), and the duration of exposure. (9)

Protection Requirements

Protection requirements for canisters are generally defined based on the chemical threat, the exposure scenario (such as battlefield versus occupational exposure), and the controlling legal authority for the wearer's safety and health. The Office of the Surgeon General of the U.S. Army has been assigned the overarching responsibility for the safety and health of military personnel in military-unique environments, including the responsibility for certifying personal protective equipment (PPE) requirements. (10) The U.S. Army Chemical, Biological, Radiological, and Nuclear School establishes specific protection requirements for military mask systems (including filtration canisters and elements).

The chemical threat to the M40 series filter canister is defined in terms of the minimum number of chemical attacks that the canister must be capable of withstanding for a specified CWA. A chemical attack is commonly expressed as the product of the agent concentration (C) and the duration (T) of the attack as follows:

Chemical attack = C (milligrams/[meter.sup.3]) x T (minutes), or CT (milligram-minutes/[meter.sup.3])

The cumulative chemical agent threat for a specific CWA, or total CT, is expressed as the product of the CT and the total number of attacks as follows:

Total CT (milligram-minutes/[meter.sup.3]) = [concentration (milligrams/[meter.sup.3]) x time (minutes)] x [number of attacks]


The protection afforded by the filter canister is expressed as the percent penetration of a CWA threat challenge with exposure to the total CT. The percent penetration represents a threshold accumulated dose of a specific CWA that typically produces a physiological effect on the wearer and is unique to that CWA.

In 1999, based on available toxicological and human/animal dose-response data, the U.S. Army Center for Health Promotion and Preventive Medicine established short-term military exposure guidelines for deployed military personnel. These guidelines were developed for use by military commanders as a risk mitigation tool when assessing the potential safety and health risks associated with exposure to CWAs and military chemical compounds. In practice, however, these guidelines would be more applicable in military-unique situations where the threat scenario is better known and controlled (chemical demilitarization operations) versus battlefield chemical attacks. (11) In 2010, the U.S. Army Public Health Command (USAPHC) (formerly known as the U.S. Army Center for Health Promotion and Preventive Medicine) revised the existing risk assessment methodology and expanded the range of existing military exposure guidelines to include TICs. (12)

In contrast, the Occupational Safety and Health Administration has the overarching responsibility for the safety and health of nonmilitary personnel (including first responders and personnel involved in manufacturing) in occupational and workplace exposure scenarios. General requirements for occupational safety and health standards are covered in Part 1910 (Occupational Safety and Health Standards), Title 29 (Labor), Code of Federal Regulations (CFR).13 Section 1910.134 (Respiratory Protection), Subpart I (Personal Protective Equipment), covers standards for PPE--including when and how PPE is used. (14) Briefly, the Occupational Safety and Health Administration requires that employers perform a hazard assessment of the workplace, select appropriate PPE based on anticipated hazards, assess the fitness of employees to wear or use the PPE, and train employees on the proper use and maintenance of the PPE. Further details regarding employer responsibilities are outlined in Section 1910.134. (15)

The National Institute for Occupational Safety and Health (NIOSH) establishes exposure guidelines for nonmilitary personnel in the workplace. NIOSH also certifies the suitability and effectiveness of some PPE for use in nonmilitary work environments--but does not certify or approve PPE for military use. The requirements for testing and NIOSH approval of nonmilitary respiratory protective devices are covered in Part 84 (Approval of Respiratory Protective Devices), Subchapter G (Occupational Safety and Health Research and Related Activities), Title 42 (Public Health), CFR. (16)

The NIOSH Pocket Guide to Chemical Hazards (17) provides recommended exposure limits, which reflect a time-weighted average exposure concentration for a 40-hour workweek (or up to a 10-hour workday). It also presents exposure concentrations that are immediately dangerous to life and health; permissible exposure limits; and short-term exposure limits that reflect a 15-minute, time-weighted average exposure that should not be exceeded at any time during a workday. The NIOSH-established TIC exposure guidelines for nonmilitary personnel in the workplace do not necessarily correlate with the military exposure guidelines established by the USAPHC for military personnel in military-unique environments.

Filter Change-Out Criteria

Filter change-out guidelines for military applications--including guidelines for the C2A1 canister--are contained in Field Manual (FM) 3-11.4, Multiservice Tactics, Techniques, and Procedures for Nuclear, Biological, and Chemical (NBC) Protection. (18) Specific change-out criteria are provided for the peacetime, transition-to-war, and wartime use of the protective mask system. In each of these use scenarios, the anticipated threat, climatic conditions, the filter design, and the condition of the filter must be considered. During peacetime, filters that are wet or clogged, have sustained physical damage, or have exceeded their expiration date are routinely changed out. In some peacetime situations, expired filters that are not clogged or damaged can be used for training. During the transition to war, field commanders must consider the unit mission and readiness/deployability alert status, anticipated terrain and weather conditions, the chemical-biological threat assessment for the mission, and the availability of filters and personnel to conduct filter change-outs.


During wartime, filter change-out is based primarily on the types and amounts of chemical agents to which the canister has been exposed and the length of time the filter has been out of its original packaging and exposed to the atmosphere. Wartime change-out intervals (expressed in terms of "war weeks") are also based on climatic conditions. Filter performance tends to be most quickly degraded under hot and humid conditions; therefore, more frequent change-outs are required under these conditions than under other climatic conditions. Units that have been subjected to chemical attacks change out their filters at least every 30 days.

In contrast, nonmilitary occupational or workplace chemical exposure scenarios are generally considered better defined and controlled. Section 1910.134, Subpart I, Part 1910, Title 29, CFR (19) requires employers to ensure that respirators with filter cartridges are equipped with NIOSH-approved, end-of-service-life indicators for specific chemical threats. If no end-of-service-life indicator is appropriate for the conditions encountered in the workplace, the employer is required to implement a filter cartridge change-out schedule to ensure that filters are replaced before the end of their service lives. The change-out schedule is based on objective evidence or on data available for the specific workplace threat.

Canister Conundrum

Differences in military or occupational workplace chemical threats, protection requirements, and filter change-out criteria have created a conundrum regarding military C2A1 canisters versus commercial canisters. Are commercial "look-alike" canisters interchangeable with the C2A1 canister that is authorized for use with the M40 series mask? The simple answer is "No!" While the two canisters may look alike, appearances can be deceiving. The C2A1 canister was specifically designed and extensively tested for use with the M40 series protective mask, and the C2A1 and C2 canisters are the only canisters authorized for military use with the M40 series mask.

The commercial FR-C2A1 canister is NIOSH-approved for occupational-exposure scenarios only when used with the FR-M40 mask (which is a close commercial variant of the M40 mask that is also manufactured by 3M). The pairing of the FR-C2A1 canister with the M40 series mask is not authorized for military use or NIOSH-approved for nonmilitary use. The same is true for other commercial canisters that are paired with the M40 series mask. Mixing and matching military and commercial masks and canisters can be risky. Do not be fooled by look-alike commercial canisters; genuine military masks and canisters can only be acquired through authorized military supply channels. The bottom line for filter canisters is: If it isn't authorized for the M40 protective series mask, don't use it!


(1) "M40/M42-Series Protective Mask," Army Study Guide, < _Equipment_Information/CBRN_Equipment_Information /m40m42series-field-protec.shtml>, accessed on 11 September 2012.

(2) Joseph T. Maheady et al., (Edgewood Chemical Biological Center Technical Report 930), M40A1/M42A2 Chemical Biological Mask Internal Drink Tube Redesign Operations and Support Cost Reduction, 2012.

(3) Ibid.

(4) "Test Criteria for the 3M[TM] Cartridge FR-C2A1 Against Various Military and Industrial Chemical Agents," 3M Technical Data Bulletin No. 152, Occupational Health and Environmental Safety Division, 3M, St. Paul, Minnesota, February 2009, < erver?mwsId=SSSSSu7zK1fslxtU48_vo8t1ev7qe17zHvTSev TSeSSSSSS-->, accessed on 12 September 2012.

(5) Convention on the Prohibition of the Development, Production, Stockpiling, and Use of Chemical Weapons and on Their Destruction (Chemical Weapons Convention), 3 September 1992.

(6) FM 3-11.9, Potential Military Chemical/Biological Agents and Compounds, 10 January 2005.

(7) Ibid.

(8) Ibid.

(9) Ibid.

(10) Army Regulation (AR) 385-10, The Army Safety Program, 23 August 2007.

(11) USAPHC Technical Guide 230 (Provisional), Environmental Health Risk Assessment and Chemical Exposure Guidelines for Deployed Military Personnel, June 2010.

(12) USAPHC Reference Document 230 (Provisional), Methodology for Determining Chemical Exposure Guidelines for Deployed Military Personnel, June 2010.

(13) CFR, Title 29 (Labor), Part 1910 (Occupational Safety and Health Standards), current as of 13 September 2012.

(14) CFR, Title 29 (Labor), Part 1910 (Occupational Safety and Health Standards), Subpart I (Personal Protective Equipment), Section 1910.134 (Respiratory Protection), current as of 13 September 2012.

(15) Ibid.

(16) CFR, Title 42 (Public Health), Subchapter G (Occupational Safety and Health Research and Related Activities), Part 84 (Approval of Respiratory Protective Devices), current as of 13 September 2012.

(17) NIOSH Pocket Guide to Chemical Hazards, Centers for Disease Control and Prevention, 8 February 2012, <>, accessed on 17 September 2012.

(18) FM 3-11.4, Multiservice Tactics, Techniques, and Procedures for Nuclear, Biological, and Chemical (NBC) Protection, 2 June 2003.

(19) CFR, Title 29, Part 1910, Subpart I, Section 1910.134.

By Mrs. Mary P. "Trish" Weiss, Dr. John R. Kennedy, and Mr. James K. Church Jr.

Mrs. Weiss is a senior mechanical engineer and team leader with the Individual Protection Equipment Branch, Edgewood Chemical Biological Center. She holds a bachelor's degree in mechanical engineering from North Carolina State University, Raleigh, North Carolina, and a master's degree in program management from the Naval Postgraduate School, Monterey, California. Mrs. Weiss is a member of the U.S. Army Acquisition Corps; and she has 28 years of experience in the areas of individual and collective protection equipment, tactical smoke weapons, and chemical demilitarization operations.

Dr. Kennedy, who is a retired U.S. Army Reserve lieutenant colonel, is now a physical scientist with the Edgewood Chemical Biological Center. He holds a bachelor's degree in chemistry from New Mexico State University, Las Cruces, New Mexico; a master's degree in physical chemistry from Texas Tech University, Lubbock, Texas; and a doctor of philosophy degree in physical chemistry from Texas A&M University, College Station, Texas. Dr. Kennedy is a graduate of the U.S. Army Command and General Staff College, Fort Leavenworth, Kansas, and the College of Naval Command and Staff, U.S. Naval War College, Newport, Rhode Island. He is a member of the U.S. Army Acquisition Corps.

Mr. Church is a senior chemical engineer and chief of the Physical Protection Equipment Branch, Edgewood Chemical Biological Center, Aberdeen Proving Ground, Maryland. He holds a bachelor's degree in chemical engineering from Virginia Polytechnic Institute and State University, Blacksburg, Virginia, and a master's degree in management and supervision from Central Michigan University, Mount Pleasant, Michigan. Mr. Church is a member of the U.S. Army Acquisition Corps; and he has 34 years of experience in the areas of developing, testing, and producing individual protection equipment; developing alternative technologies; and ensuring domestic preparedness.

DISCLAIMER OF ENDORSEMENT: Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the U.S. Government or the U.S. Army Chemical, Biological, Radiological, and Nuclear School. The views and opinions of authors expressed herein do not necessarily state or reflect those of the U.S. government or the U.S. Army Chemical, Biological, Radiological, and Nuclear School and shall not be used for advertising or product endorsement purposes.
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Author:Weiss, Mary P. "Trish"; Kennedy, John R.; Church, James K., Jr.
Publication:CML Army Chemical Review
Date:Dec 22, 2011
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