In the previous article, we outlined how testing in standards can be applied to materials, components, and assemblies or full “systems.” “Systems testing” relates to the evaluation of complete “elements” whether it be a helmet, boot or garment.
While systems testing is harder to perform and involves greater variability than tests on small parts of the PPE product, it provides information on how the entire product can perform in ways that cannot be determined by individual material or component tests.
After detailing how the “shower” test has helped to create garment designs that keep firefighters drier and give better protection from exposure to hazardous liquids, we can focus on MIST — man-in-simulant testing. We’ll also outline suggestions on how fire departments can conduct their own systems testing to understand the limitations of their ensemble clothing choices.
By Jeffrey O. and Grace G. Stull
The characterization of liquid and hazardous substance protection for turnout and related clothing is undertaken through a series of material barrier tests and overall systems tests. For liquid protection, this performance is demonstrated through small-scale tests where material samples and seams are challenged with various representative chemical substances. If liquid penetration is detected, the material or the seam is considered to have failed. The shower test described in our previous column provides the overall assessment of the product design, evaluating features that cannot be easily tested on a small scale.
Presently, turnout clothing is not tested for vapor protection except in the case where the CBRN (chemical-biological-radiological-nuclear) protection option is selected. This option provides a higher level of testing for firefighter protective ensembles that permits firefighters to safely escape in the event they encounter hazardous substances during terrorism events. The CBRN option significantly increases fire fighter protection against exposure to vapors, since conventional turnout clothing does not readily retard the penetration of vapors. As most structural fires involve the generation of toxic gases, some of which become adsorbed onto the soot particles that in turn soil clothing, some level of vapor protection can be considered beneficial in non-CBRN terrorism events.
In the case of vapors versus liquids, different test approaches have to be used. Instead of a liquid penetration test, a permeation test is used. Chemical challenges are applied as either liquids or vapor, but the level of detail in determining the passage of chemical is much more severe as analytical instruments are used to determine if small amounts of chemical “permeate” through the material.
To prevent this permeation, aggressive barrier materials must be used but these materials must also be breathable. The most difficult challenge is designing the ensemble to keep vapors from entering the ensemble through the various interface aeas. These interface areas include where the gloves join coat sleeves, the front closure of the coat, and the particularly open area of the head where hood, helmet, SCBA facepiece, and coat collar come in contact.
Employed by military
A comparative evaluation of ensembles for demonstrating protection against chemical vapors and air borne biological agents is conducted using the Man-In-Simulant-Test (MIST). This technique, employed by the military for years for testing battlefield chemical warfare agent protective clothing, is now used for testing first responder ensembles in NFPA 1994 (terrorism protective clothing) and for the CBRN options of NFPA 1971 and NFPA 1951.
MIST involves the placement of special adsorbent pads on test subjects at several different locations. The test subjects then wear the ensemble (consisting of the garments, helmets, gloves, footwear and SCBA) and perform a series of exercises replicating response activity inside a closed chamber. A non-harmful surrogate chemical agent for mustard gas (methyl salicylate) is maintained at a specific concentration during the test period.
After the 30-minute exposure, the adsorbent pads are removed from the test subjects and then analyzed to determine how much surrogate chemical penetrated the ensemble and onto the pads. The results are taken from individual body locations based on the position of the adsorbent pads and provided information at to where any leakage occurs and how much chemical would be absorbed onto the skin. The information from all of the pads is also used to provide an overall protection factor for the ensemble.
The protection factor is the ratio of the outside agent concentration to the inside concentration of surrogate agent collected on the pads. Protection factors are commonly used in respirator protection to show how the PPE must reduce the exposure to the individual from the outside contaminated environment. Higher protection factors mean greater protection.
NFPA standards
Specific protection factors have been set for the CBRN option in the various NFPA standards. For the Class 2 ensembles of NFPA 1994 (terrorism protective ensembles) and the CBRN option in NFPA 1971 (structural protective ensembles), a minimum overall protection factor of 360 is required. Individual location-by-location protection factors for NFPA 1994 Class 2 and the NFPA 1971 CBRN option must be at least 361.
These requirements were based on an analysis of exposures of individuals to both mustard and sarin gases, in which no irreversible exposure effects occur. However, this same level of integrity is suitable for demonstrating no effects for most highly toxic chemicals and carcinogens. As a matter of perspective, when conventional turnout clothing is tested, the protection factors range from 10 to 20.
This range explains why many vapors or gases will readily penetrate and permeate the clothing and result in exposure at only a slightly reduced level, compared to what concentrations occur in the contaminated atmosphere. While MIST is currently only intended for specialized ensembles and CBRN option turnout clothing, it provides an understanding that your skin will likely be exposed to the many gases or vapors that are found at emergency responses.
Understanding clothing limitations is the subject of another type of systems evaluation, one that fire departments often perform on their own. As much as the NFPA standards attempt to define minimum protection requirements, there are some areas where requirements are not easily established. One such case is in the area of how the selected turnout clothing affects an individual firefighter’s movement, function, and comfort. These assessments are critical because the demonstrated performance offered by the PPE must permit the firefighter to safety perform his or her duties with the least physical exertion.
It is important that fire departments routinely conduct their own “systems” testing to determine if they have selected design features that are desired and if all parts of the ensemble – coat and pants, helmet, gloves, footwear, hood, and SCBA – work together as intended. These types of evaluations can only be performed with the firefighter and for the most part, results are firefighter-specific since the sizing of each PPE element will play a key role in affecting firefighter movement. This type of systems tests is best performed under controlled circumstances involving exercises that represent the range of emergency scene activity where clothing protective qualities are paramount.
The majority of the assessments are subjective in nature; however some ways to quantify results can be made when ratings are used for specific categories of movements and firefighter perceptions of comfort. Based on these results, fire departments can evaluate features and compare products. But more importantly, individual firefighters gain a realization for how their gear will affect their mobility and activity during an emergency.
Systems testing is a key part of the overall evaluation of turnout clothing. While there are only a few types of tests regularly applied to protective garments as part of the formalized standards process, methods do exist to assess overall clothing and ensembles. Applying standard or generalized methods will help create awareness for how clothing is likely to provide protection and affect wearer function under a variety of exposure circumstances.
End Note: Recently, Jeff and I observed several MIST and shower tests. We enjoy sharing our observations with our readers. Thank you for your continued questions. Please remember 9/11 and our firefighter heroes.
