Editor’s note: This is the second part of a look at the testing changes planned for hazmat protective clothing. Check out the first part here.
Cumulative permeation is already used for the determination of permeation resistance for NFPA 1991 suit materials from chemical warfare agents. It is similarly applied to clothing materials specified in NFPA 1951 (CBRN technical rescue operations protective ensembles), NFPA 1971 (CBRN option for structural fire fighting protective ensembles), and NFPA 1994 (CBRN terrorism protective ensembles) for specialized forms of chemical barrier protection.
Specific levels of acceptable performance have been set at 1.25 μg/cm2 for nerve agents (Sarin or Soman) and 4.0 μg/cm2for blister agents (distilled mustard). Nerve and blister agents are by far some of the most skin toxic substance known to man.
Yet, the vast majority of industrial chemicals have skin toxicity levels that do not come close to approaching the low levels for chemical warfare agents, which are designed to be lethal through skin absorption.
Furthermore, the NFPA committee has already accepted the use of cumulative permeation for certain toxic industrial chemicals, including acrolien, acrylonitrile, ammonia, chlorine, and dimethyl sulfate.
The acceptable level for cumulative permeation has been set at 6.0 μg/cm2 for these chemicals. So the question one should really ask is if cumulative permeation is already being used now for the really toxic chemicals and the level being proposed for NFPA 1991 is about the same for chemical warfare agents, why is it being questioned.
Cumulative permeation is a better measurement of material barrier performance because it accounts for problems in how permeation is determined using breakthrough time and it provides the future opportunity to refine limits with the prospects of promoting better protective ensembles.
Without going into the detail, standard test techniques for determining breakthrough time can miss spurious peaks in chemical permeating the material because only periodic sampling is used in testing.
Comparatively, the measurement of cumulative permeation means that the laboratory has to capture all chemical going through the material. This makes cumulative permeation a more reproducible and accurate measurement.
It is impossible to relate breakthrough time directly to safe limits of exposure for hazardous chemicals. Chemical exposure limits are based on the acceptable exposure limits, which in turn require an understanding of the dose and the length of time for which exposure occurs at a specific chemical concentration.
The use of cumulative permeation offers a means for relating acceptable dose to experimental determinations of material permeation performance.
Even when the criteria based on cumulative permeation use extremely conservative limits as has been proposed, it is possible to make adjustments in the future to link acceptable exposure limits to corresponding levels of cumulative permeation.
The recommendation for switching from the non-meaningful breakthrough time to a toxicity-based cumulative permeation mass (dose) for measurement of permeation resistance affords a safe, reasonable, and conservative criterion.
It is the first logical step for the NFPA committee responsible for encapsulating chemical protective suit standards to take in moving toward vapor-protective ensembles that are potentially form-fitting, more comfortable, and safer to wear, without any loss of protection or safety for the end user.
Just as the structural firefighting clothing industry made its transition to TPP many years ago, it is now time to shift the chemical protective clothing industry to a way of qualifying chemical barrier materials that targets useful information that can be related to exposure effects.
The use of breakthough time cannot accomplish this change and is akin to the use of thickness as the yardstick for assessing bunker clothing effectiveness.
As we have reported many times in the past, a test is only appropriate if it can be properly validated through science and field observations. That science has gone into the development of cumulative permeation as a measurement technique whereas the determination of breakthrough time is simply arbitrary assessment.
As breakthrough time defines the current chemical protective clothing industry, it is like the tail wagging the dog, instead of the other way around.
