The ASTM F739 testing protocol, “Test
Methods for Resistance of Protective Clothing Materials
to Permeation by Liquids and Gases” is used to evaluate
fabrics’ resistance to permeation through the
material. An appropriate piece of the fabric to be
tested is placed in an apparatus as depicted in Figure
1. The “outside” surface of the fabric is exposed
to the liquid or gas against which the fabric is being
tested. The “inside” surface faces the sampling
portion of the apparatus.
Figure 1 – ASTM F739 Testing
As the chemical moves
through the fabric, the analytical device (“analyzer”)
connected to the sampling chamber will detect it.
The sensitivity of the “analyzer” will vary depending on
the chemical being tested.
permeation is a misunderstood process. It is not
chemical moving through holes in the fabric. It is
actually the fabric absorbing the chemical and becoming
saturated with the chemical and then desorbing the
chemical on the “inside” surface. When this occurs
and there is sufficient chemical present in the sampling
chamber such that the analyzer can detect the chemical,
then actual breakthrough has occurred. A typical
test period for permeation is 8 hours, if no permeation
is detected, the material will be reported with a
breakthrough time of >480 minutes. The reported
breakthrough times are typically based on the average of
multiple tests. A >480 minute breakthrough time
does not mean permeation didn’t occur, it just means
none was detected.
Another problem with fabric testing
and its relation to real-world use is that only single
pieces of fabric are tested for permeation rates.
In the real-world suits, boots and gloves may have seams
in the product that allow the fabric to be constructed
into a shape that will fit a hand, foot or body.
In addition, suits will have seams that allow entry and
exit into the products but then must be sealed for
use. Likewise, there are those areas where one
garment type interfaces to another garment type, e.g.,
gloves to the suit or boots to the suit. As
everyone that has been through basic HAZMAT training
knows, it is important to seal these interfaces to
prevent chemical exposure. Manufacturers don’t
report breakthrough times or permeation tests performed
on these seams and interfaces, yet they are probably the
most susceptible to chemical permeation and the eventual
chemical exposure by the user.
The user of
Chemical Protective Clothing (CPC) products must keep
these facts in mind and understand what the test and the
results represent with regard to real-world
adapted this figure and portions of this discussion from
DuPont de Nemours and Company’s Tychem®
Chemical Protective Clothing