Answer: Ask Frank...
One of the confusing and commonly misinterpreted aspects of chemical suit selection is the chemical permeation test – used by many as a simple indication of the effectiveness of a chemical suit as part of a selection process. However, the test result most quoted and used – the “Breakthrough” – more correctly called the “Normalised Breakthrough” – and quoted in minutes, is not actually, at least in the way most of us would understand the term, a “breakthrough”. So what is it?
What is Normalised Breakthrough in a Permeation Test?
The result of a permeation test (in Europe EN 6529) is often quoted as >480 Minutes. Right now, many people - understandably given the terminology - interpret this as:-
“None of the chemical has broken through the fabric in 480 minutes, therefor I am safe for at least 480 minutes”.
…which seems logical. Unfortunately this is not what “breakthrough” means. In fact “Normalised Breakthrough” has a very specific definition and it is NOT “when the chemical first breaks through the fabric”.
The “breakthrough” is defined as:-
“The time taken until the RATE or SPEED that permeation is taking place reaches 1.0 microgram per minute per centimetre squared – that is, a rate of 1.0µg/min/cm2. The “breakthrough” is therefor recorded at the point that permeation reaches a particular speed, and not when it first begins.
(* Note: in the US ASTM equivalent test 0.1µg/min/cm2 is used)
You may immediately realise the implication of this; that at the point of “breakthrough” in the test, the chemical has already been permeating through the fabric…
This can be best understood by considering a graph of a hypothetical chemical; The gap between the first identified breakthrough (A) and the normalised breakthrough (B) at 1.0µg/min/cm2 is180 minutes (C). For this period the chemical has been permeating through the fabric at an increasing rate… (and note that the shaded area below the line (D) represents the volume permeated over time…)
There is no need for panic at this revelation – if a revelation it is; First, with a >480 minute result permeation may not have taken place at all (although you simply do not know if it has or not just from the “breakthrough” time); and second, we are discussing VERY small amounts of chemical. A “gram” (g) is tiny, and a microgram (µg) is one millionth (or 0.000001) of a gram. So permeation at less than 1.0µg/min/cm2 is not likely (depending on the chemical) to be critical. And of course, it will happen only IF contact with the chemical has occurred and been maintained. The problem is that different chemicals have very different levels of toxicity… so “not likely” is not good enough. It could be critical… and right now too many people are not even aware permeation may be occuring…
The obvious implication of this is that permeation test breakthrough CANNOT be used as it is now very commonly used – to indicate safe use times; it simply does not supply sufficient information (and incidentally, the EN 6529 test standard itself confirms this, stating that it is for comparison purposes only and is not suitable to indicate safe levels of exposure). Which leaves us with a problem:-
“How do you know how long you are safe?”
Well you might be relieved to hear that there IS a solution and we’ll cover this and related issues in more detail in future blogs. But as a starter, I would recommend reading this article in the November issue of Health and Safety International about Frank Schaaf, Head Nurse at Evonik in Antwerp.
Why read this article in particular? Because Frank has the answer…
Or, you can also download our '10 Common PPE Misconceptions' eBook to find out the myths that revolve around PPE safety standards: