Gas Mask and Respirator Wiki

The M50 and M51, officially the Joint Service General Protective Mask (JSGPM) is a lightweight, protective mask system consisting of the mask, a mask carrier, and additional accessories. The mask was designed to incorporate state-of-the-art technologies to protect US and allied forces from current and anticipated CBRN threats. It is an above-the-neck, chemical-biological (CB) respirator that protects against battlefield concentrations of CB agents, toxins, toxic industrial materials, and radioactive particulate matter. The M50/51 masks replaced the M40 and M42, MCU-2/P series of masks, and the M45 in the Land Warrior Program. There are two mask variants: the M50 (ground and shipboard use) and M51 (ground vehicle use).[1] Other variants were developed based on the M50 design for specific needs of certain military populations such as the M53 for the Special Operations Forces (SOF) community. Foreign military sales versions of the mask are also available with similar or identical specifications.


In the mid-1990s, the M40 series masks were replacing the old M17 series throughout the armed forces of the United States but CBDCOM (later SBCCOM) was already looking forward to the next mask series.  The program managers gathered information from all viewpoints, to include:

JSGPM prototype

Field Experience[]

Reports from the field indicated that the M40 series mask was described as too bulky and heavy for modern military operations.  The decision to move to the large external C2 and C2A1 filter elements for the sake of NATO standardization made the mask bulkier (although lighter) than its predecessor, the M17.  The M40 mask carrier earned the derogatory nickname, "the suitcase" due to the large size and cumbersome handling in the field.  When the mask is worn, the filter element stuck out of the face blank of the mask and became a natural "lever arm" that could break the seal of the mask when working in confined spaces or simply through the rigor of combat operations. The field of view of the M40 series and other masks were deemed inadequate for sustained operations and the mask's ability to interface with current sighting and other optical devices was poor. 


Intelligence agencies were growing increasingly concerned with the development and proliferation of 4th generation nerve agents--the so-called Novichok agents.  These agents were developed specifically to defeat western detection and protection systems and it was not clear whether current filter technology could adequately deal with the threat. Developing filter systems that could address these newcomer agents was a top force protection priority.

Operational Planning[]

From an operational aspect, it was clear from Operation DESERT STORM and subsequent conflicts that servicemembers were increasingly being exposed to toxic industrial chemicals and materials on the battlefield from which current mask systems had an unknown protective capability.  A mask that could filter out common industrial hazards would greatly assist sensitive site exploitation and other military operations. 


Accountants complained that the complexity of the M40 series was increasing the life-cycle costs of the M40 to an undesirable level. Simplifying the design by lowering part counts and increasing the reliability of the next mask system would go a long way to decrease the life-cycle costs of the next mask series. Additionally, economies of scale could significantly lower costs if all armed service could use the same mask system instead of having many models spread out among the services.

Design Goals[]

Program managers, industry partners, and end-users from all services contributed to an ambitious set of design goals for the new M50 protective mask to include:[2]

  • Improve performance against chemical and biological agents, toxic industrial materials and nuclear fallout,
  • Improve field of vision,
  • Reduce weight and bulk,
  • Reduce breathing resistance by half over currently fielded masks,
  • Make the mask more comfortable
  • Improve equipment compatibility e.g. JSLIST, night vision devices, optical sites, helmets, etc.,
  • Reduce the size of filter elements and shape it in different configurations to fully integrate it into the mask, 
  • Color code repair parts for easy identification,
  • Integrate a filter shelf-life indicator,
  • Ability to safely and quickly change filters while in a contaminated environment,
  • Improve drinking system for easier use and greater flow of liquids,
  • Fully integrate the mask into the warfighter's combat ensemble for the next generation, 
  • All maintenance to be at the operator and unit level with limited repair using replacement parts,
  • Reduce the number of repair parts from 36 for the current mask to 12,
  • Reduce total ownership costs by at least 50 percent over current masks.


XM50 with the clear silicone rubber nose cup assembly and bright orange internal valves. The production M50 mask had a black nose cup and valves.

Computer-aided design and airflow computer models were used extensively in the design of the mask.  Consequently, there were few actual prototypes used in the development of the mask however, there were several mockups to illustrate different features for decision-makers.  The XM50 was the first fully functional prototype used in the testing phase of the mask.  The XM50 looks nearly identical to the M50, however, the XM50 can be distinguished from actual production models due to its clear silicone rubber nose cup assembly and the use of orange-colored rubber for the internal valves.[3] The production M50 mask has a black rubber nose cup and black internal valves. In the development of the M50, the XM50 was put on a unique and innovative modelling and simulation test fixture that was developed to allow a more realistic form, fit, and function of the mask during evaluations using live agents, ensuring maximum real-world protection.[2]


The M50 is the actual production model produced by Avon Protection Systems, Incorporated, in their production plant in Cadillac, Michigan.  While other masks have been produced in larger quantities, the fielding of the M50 mask series is the single largest Department of Defense (DOD) mask fielding effort since 1947.[4] The foreign military sales version of the M50 is the FM50. The FM50 is identical to the M50 and intended for allied military sales.[5] Avon Protection Systems makes a civilian version of the M50 known as the Avon C50 marketed towards first responders. The M50 and C50 are identical except that the C50 accepts standard 40mm NATO filter canisters as well as a variety of special-purpose filters.[6]

The facepiece assembly, head harness, eye lens outsert assembly, front module assembly, M61 filters, and drink tube coupler and housing are the principal operating components of the M50 Field Protective Mask.[7]  

  • Facepiece Assembly - The facepiece assembly is the foundation of the protective mask and everything else is attached to it.  The facepiece assembly is made of chlorobutyl rubber-silicone blend giving the mask a high degree of flexibility and comfort for extended use.  The chlorobutyl content of the rubber formulation limits permeability to chemical warfare agents, however, a hood/second skin is still available for more comprehensive protection.  The facepiece is designed with an inverted peripheral face seal and an integrated chin cup. The facepiece assembly incorporates a flexible, single, polyurethane eye lens; a front module that provides a direct speech capability and integrates the exhalation disk valve, drinking system components, and communications interface; two filter mounts (left and right) that integrate the air inlet/outlet disk valves, self-sealing disk valves, air deflectors; and a nose cup that controls the flow of air throughout the mask.[7] The mask is issued with a plastic face form to help the facepiece maintains its shape and avoid permanent set. The facepiece comes in small, medium, and large sizes and is designed to fit 98% of the user population.[8]
  • Head Harness - The head harness is the adjustable straps that are attached to the facepiece assembly.  When adjusted properly, they will secure the facepiece assembly to the wearer's face creating an airtight seal.  The head harness consists of a skull cap, and elasticized brow straps, temple straps, and cheek straps.  The head harness was designed to avoid pressure points and provide a comfortable mask fit.[7]
  • Eye Lens Outsert Assembly - The clear outsert assembly provides the eye lens protection against scratching or other damage.  It has the same contour as the eye lens and clips over the eye lens using outsert locking tabs that do not interfere with the wearer's vision.  The clear outsert is issued with an outsert pouch which can also be used to clean the mask.  The clear outsert is stowed attached to the mask; the outsert pouch will be stowed in the outsert pocket located on the outside of the mask carrier.  Use of the clear outsert or neutral gray sunlight outsert provides additional ballistic protection. Laser protective (green) and high contrast (yellow) outserts are also available for special missions.[7]
  • Front Module Assembly - The front module consists of a plastic housing (Front Module Main Body) that integrates the inlet/outlet disk valve and drinking system components. The outlet valve cover assembly fits over the front module's main body protecting the drinking system and outlet disk valve.  It has a communications port cover to protect the "prewired" communications port.  The outlet valve cover is dark gray in color and the design of the cover provides a direct speech capability.[7]
  • There are three black colored inlet/outlet disk valves contained in the facepiece assembly:  One is located between the outlet valve cover assembly and the front module main body assembly.  It serves as an outlet valve disk and releases exhaled air while preventing unfiltered air from entering the facepiece assembly.  The other two are located in the interior of the facepiece assembly and are attached to the rear of the left and right filter mounts.  They serve as inlet disk valves and permit filtered air to enter the mask.[7] 
  • Self-Sealing Disk Valve -  There are two, clear colored self-sealing disk valves in the facepiece assembly.  Replacement valves for the mask have been white in color. They are located on the exterior of the facepiece assembly and attach to the front of the left and right filter mounts.  The M61 filters are attached to the filter mounts using a twist and locking mechanism.  When the filter is attached to the filter mount, it opens the self-sealing disk valve permitting filtered air to pass through the inlet disk valve during inhalation. When the filter is removed, the self-sealing disk valve closes, preventing air from entering the mask. This allows the change of the filters (one at a time) in a contaminated environment.[7]
  • Drinking System:  The drinking system is integrated into the front module's main body and consists of an external drinking tube fitted with a drinking cap to link to the canteen and an internal drinking tube fitted inside the mask.  A lever arrangement opens the drinking tube safety shutoff valve and causes the internal drinking tube to swing to the wearer’s mouth.[7] The drinking system connector is not compatible with the older connector that worked with the M17, M40, and M45 series masks. A new canteen cap with the newer drink tube connector was typically issued with the M50 mask.
  • Filters:  Twin, low profile M61 filter elements, one installed on each side of the mask, provide protection from CBRN agents.  The M61 filters contain activated carbon media and a high-efficiency particulate filter. A patch assembly is located on the back of the M61 filter to show the health of the filters based on time out of its protective packet. Filter alignment marks are molded into both the M61filters and the facepiece assembly to ensure the proper attachment.[7]
  • Nose Cup Assembly:  The nose cup assembly is located inside the facepiece assembly.  The nose cup assists in controlling the flow of air throughout the mask to minimize the fogging of the eye lenses during breathing.  The nose cup size (S, M, L) and the internal drink tube alignment arrow are located on the left interior side of the nose cup. During exhalation, the positive pressure created inside the mask closes the inlet valves and opens the outlet valve housed in the front module main body assembly.  The nose cup channels the moist expired air directly through the outlet valve to the outside environment.[7]


The M51 (FM51 foreign military sales designation) is designed for crewmen of armored vehicles with a ventilated facepiece-type collective protection systems.  The mask is the same as the M50, but has a few extra items to interface with the vehicle's communication system and collective protection system:

  • Microphone, Microphone Adapter, and Communications Lead: The microphone is attached to a microphone adapter that is attached to the communications port in the front module main body inside the facepiece assembly. One end of the communications lead is connected to the communications port on the front of the front module assembly; the other end is connected to the combat vehicle helmet and provides the capability for on-vehicle communications. The microphone and microphone adapter are stored installed inside the mask.[8]

    M51 showing hose assembly and fire-resistant hood. Image from PS Magazine.

  • Hose Assembly: The hose assembly provides a connection between the mask and the vehicle collective protection system. One end of the hose connects directly to the M61 filter. The filter connector swivels, accommodating head and body movement. The other end connects directly to the vehicle collective protection system. The hose is attached to the service member's uniform using the Clothing Clip to prevent the hose from pulling the mask away from the face.[8]
  • Protective Hood: The protective hood is made of a flame-resistant material that protects the service member from CBRN vapors, aerosols and liquids. Additionally, the protective hood protects the service member for a short duration of time during an emergency escape from vehicle fires (the JSLIST hood provides a similar function for the M50 mask although the JSLIST hood is not fire-resistant). The protective hood attaches to the mask and is placed over the service member's head. The mask is stowed with the protective hood attached.[8]

M61 Filter Elements[]

The M50 series mask accepts the twin M61 filters; a specially designed low profile filter that improves the service member's ability to interact with equipment such as a shoulder-fired rifle or night vision goggles.  In a throwback to the M17 series mask, the filters are mounted to either side of the mask to provide an evenly weighted balance to reduce the wearer's fatigue of the neck and upper back muscles.  Unlike the M17 series mask, the filter elements are located on the outside of the mask and can be changed in a contaminated atmosphere due to the self-sealing filter mounts.  The large filter inlets, a short path through the filter media, specially designed pleated filter media and the inclusion of two filter elements successfully reduced breathing resistance by 50% over the current C2A1 filter element, a key design goal.

The filters have a small shelf life indicator patch on the underside of the filter where the element connects to the mask. The patch begins as white when they are taken out of the vacuum-packed container and will turn blue when the filter is expired and should be changed. The patch is made with erioglaucine ammonium salt and magnesiumnitrate hexahydrate and changes colour from white to blue with the exposure to humid air. These ingredients are toxic and can cause mucous membrane irritation, but are safe as long as the shelf life indicator patch is not disturbed.  Expired filter elements should be changed immediately in an operational environment, but they still may be used for training purposes in low-risk mask confidence exercises (CS chamber).[8]

The M61 filter media is a high-efficiency particulate filter membrane with activated carbon sorbent salted with various chemical compounds designed to defeat all known and emerging chemical, biological and radiological threats as well as many typical toxic industrial chemicals and materials. It should be noted that the filter elements do not contain hexavalent chromium as some previous filter media formulations have. The M61 substitutes a non-toxic zinc-based formulation to counteract cyanogen chloride and hydrogen cyanide gas (NATO designation CK and AC respectively). The filter elements are designed to last at least 24-hours at typical battlefield concentrations of CBRN threats, matching the expected duration of the JSLIST chemical protective overgarment.[9]

The development of the M61 filters continues as new technologies, materials, and manufacturing techniques emerge. Current filter developments include:

  • High-Efficiency Synthetic Particulate Air (HESPA) filtration material - HESPA offers several advantages to the current M61 filter program. This technology greatly improves filter performance with the same M61 filter form factor.  When combined with the development of pleat encapsulation technology, the shape of the filter is no longer confined to the conventional square/rectangle or round/cylindrical flat shape, thereby providing greater flexibility in equipment design and interface.[10]

    An add-on secondary filtration element seen attached to the standard M-61 filter element.

  • Secondary Filtration Media - No one filter media formulation can protect against all conceivable threats at the same time, so an additional filter is being developed to augment the standard M61 filter for specific missions.  The additional filter simply clips onto the current M61 filter and provides an extra layer of protection for specific threats.  Secondary filters are being developed for ethylene oxide, ammonia, and formaldehyde challenges.[10]
  • ARZ-CoZZAT Sorbent - Researchers at Defense Threat Reduction Agency combined current M61 filtration materials with two new sorbents; ARZ, primarily composed of zinc chloride, and a metal oxide composite made of cobalt (Co), zinc (Z), silver (A), and triethylenediamine (T) additives (CoZZAT)  in a tri-layered M61 filter bed to improve toxic industrial chemical and chemical warfare agent protection. Unlike activated carbon, which traps poisons via relatively weak physical adsorption, CoZZAT filters these molecules by reacting with them chemically with strong covalent bonding.[11] The prototype M61 filters made with the ARZ-CoZZAT combination demonstrated effective performance against a wide range of chemical challenges, including toxic industrial chemicals and CWAs, significantly outperforming the current M61 filters. The sorbents can be incorporated into existing filtration systems, eliminating the need for filter redesign. The CoZZAT and ARZ sorbents were successfully transitioned from the laboratory to the Joint Program Executive Office for Chemical and Biological Defense to undergo further testing and begin the acquisition process. The new filters are expected to replace current M61 filters.[12]

The adoption of the M61 series filters departed from the Standard NATO Agreement (STANAG) governing NATO filter sizes (STANAG 4155) that require a 40mm screw-mounted filter with a 1/7 turn ratio.  Although the issue has generated some internal criticism and may complicate NATO interoperability and logistic issues, the US decided that the benefits of the non-standard filter design outweigh the benefits of NATO standardization.


The M53 protective mask from Avon promotional material.

The M53 (FM53 foreign military sales designation) protective mask is based on the US Government M50 (Joint Services General Purpose Mask) Program and developed by Avon Protection CBRN Products. The 53-Series Protective Mask was specifically developed to meet the unique requirements of Special Operations Forces (SOF) and is not a standard mask issued to other service members. The primary purpose of developing this mask was the flexibility it offers SOF for special missions. The mask  features a variable resistance exhalation unit (activated with a simple twist of the outlet valve assembly) that allows for the following modes of operation depending on the specific mission:

  • APR (Air Purifying Respirator)- A negative pressure mask using NATO thread filters that operate like any other CBRN protective mask. The purified air is delivered to the wearer when he breathes in, or in other words, reduces the pressure in the mask to less than outside pressure, hence the name "negative pressure."
  • SCBA (Self Contained Breathing Apparatus). The SCBA configuration is a type of supplied-air respirator that gives the user an independent air supply from a pressurized tank typically worn on the wearer's back. 
  • PAPR (Powered Air Purifying Respirator). PAPRs have air blowers to pull air through the filters and deliver the purified air to the mask wearer.
  • CCBA (Closed Circuit Breathing Apparatus). The closed-circuit type filters, supplements, and recirculates exhaled gas commonly called a "rebreather."  It is used when a longer-duration supply of breathing gas is needed.
  • Combination SCBA and PAPR.  This configuration combines the tank supplied air of the SCBA with the air blower capability of the PAPR to minimize the stress on the wearer on long-duration missions in a contaminated environment.[13]

 This protective mask was developed to counter the multiple threats encountered on the modern battlefield, war on terrorism and peacekeeping operations around the world. It provides excellent protection against traditional chemical and biological warfare agents, selected Toxic Industrial Materials (TIMs), selected Toxic Industrial Chemicals (TICs) and particulate matter including radioactive dust.

The M53 facepiece assembly is built on a butyl and silicone rubber formulation similar to the M50 and M51.  The face blank has an inverted peripheral face seal and an integrated chin cup and is available in four sizes with interchangeable silicone nose cup for a custom fit. The facepiece assembly forms a comfortable seal on the wearer’s face and protects the face, eyes, and respiratory tract from chemical and biological agents, certain TICs, and radiological particulates. The facepiece assembly incorporates a single, flexible, polyurethane eye lens; drinking system components; a communications interface; and single filter mount assemblies with a 40-mm NATO thread that integrates the inlet disk valve and air deflector.   The mask uses a single general-purpose filter, positioned on the side of the face, that provides protection against nuclear, biological, and chemical threats and certain TICs and TIMs. It should be noted that the M53 filter system is incompatible with the M61 filters used by the M50 and M51 masks. The filter can be used on either side of the mask to accommodate left and right-handed wearers. A particulate filter is also available as an additional authorization list item. A protective hood is provided for JSLIST type VII users.[14]

The communication system built into the mask is specifically designed with the SOF community in mind.  An add-on battery-powered voice projection unit can be used for verbal communication on the battlefield.  The unit is operated with a switch on the front of the unit and amplifies the voice from a microphone located in the nose cup assembly.  The unit can be used in a stealth mode with a special cable that deactivates the external headset microphone to eliminate ambient noise and to allow the user to communicate through radio with whispered communications.



  1. US Army Aquisition Support Center Page
  2. 2.0 2.1 The U.S. Army Soldier Systems Center’s (SSC) publication, The Warrior, January-February 2001, Page 12.
  3. [1]Aeon Fawkes Sales Webpage
  4. Army Chemical Review, Winter 2011
  5. FM50 Informational Brochure
  6. C50 Promotional Brochure.
  7. 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 MCRD-CBRN-1001 Employ the Field Protective Mask (FPM)
  8. 8.0 8.1 8.2 8.3 8.4 TM 3-4240-542-13&P
  9. JSLIST Article at
  10. 10.0 10.1 Joint Program Executive Office for Chemical and Biological Defense Presentation, 2007
  11. Chemical and Engineering News
  12. DTRA Chemical and Biological Technologies Department News Release
  13. Avon Protection Promotional Material
  14. Medical Management of Chemical Casualties Handbook