Our blog “Health & Safety at Work: The Hidden Killers” looked at the the nature of many chemicals that make them different to other hazards in the workplace, in that many are not only potentially hazardous in very small amounts, the hazard they present is long term. Often there are no immediate effects so that wearers of chemical suits might be contaminated by any that permeates through the fabric without even knowing. The harmful consequences – cancers, organ damage and so on – might not become apparent until months, years, even decades later.
This is bad enough for users of chemical safety clothing and safety managers charged with ensuring they are protected, but combined with a very common and basic misunderstanding of permeation test data which means that a chemical may indeed be permeating through when the wearer thinks it is not, the conclusions for companies managing chemical hazards in the workplace are worrying.
This blog looks at this global misunderstanding of permeation test data, explains why it is not what most people think it is and considers the following issues:-
- A key element for users selecting a chemical suit is the permeation test.
- The test “breakthrough” is commonly assumed to mean “no chemical has broken through”. Consequently users assume that they are safe from contamination
- However, in this context, this is a misunderstanding of the term “Breakthrough” – in fact the chemical can be permeating through the fabric before the breakthrough time.
- What this misunderstanding means for safety managers and wearers of chemical suits
Read on to discover more
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 in protecting against a specific chemical 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, at least in the way most of us would understand the term, a “breakthrough” at all. So what is it?
What is Normalised Breakthrough in a Permeation Test?
The permeation test (in Europe, EN 6529) measures the rate at which a specific chemical permeates through a chemical suit fabric, recording a “Normalised Breakthrough” as a time in minutes or as a “Class” according to the classification table provided in EN 14325. (Shown below)
The result of this permeation test is often quoted as >480 Minutes (or Class 6 in the classification table).
|Class||Normalised Breakthrough||Class||Normalised Breakthrough|
|Class 6||>480 Min||Class 3||>60 Min|
|Class 5||>2400 Min||Class 2||>30 Min|
|Class 4||> 120 Min||Class 1||>10 Min|
Currently, most managers of chemical hazards – understandably given the terminology – interpret this as:-
“None of the chemical has broken through the fabric in 480 minutes…
…therefor it is 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 in this context and it is NOT “when the chemical first breaks through the fabric”.
So What is Permeation Test “Breakthrough”?
In the context of the permeation test the “breakthrough” can be defined as:-
“The time taken until the RATE or SPEED of permeation reaches
1.0 microgram per centimetre squared per minute
– that is, a rate of 1.0µg/cm2/min”.
In other words “breakthrough” is recorded at the time that permeation reaches a particular speed, and not when it first begins.
Why is a rate of 1.0µg/cm2/min used?
In fact the standard offers two options for the point at which breakthrough is measured: 1.0µg/cm2/min and 0.1µg/cm2/min. Furthermore the equivalent test used in North America also uses 0.1µg/cm2/min . In practice the 1.0µg rate is generally used in Europe for historical reasons; a rate ten times higher than that used in North America. So why the choice of these two rates? And why the difference?
There is no particular reason for the choice of these rates other than to allow standardised comparison. The choice of either bears no relation to whether the rate selected is dangerous or not – chemical hazards in the workplace have different levels of toxicity so a particular rate might be hazardous for some chemicals but not for others. If the rate used was 0.5µg/cm2/min or 2.0µg/cm2/min it would have equal validity provided a consistent choice of rate was maintained.
The real purpose of the test is not to indicate how long a wearer is safe but to allow comparison of permeation resistance performance of different garment fabrics. (In fact the current version of the standard states:
“It can be dangerous to base considerations of safe wear time of given chemical protective clothing only on the value of normalized breakthrough time for a specific tested chemical”.
so it is very clear that providing safe-wear time is not the intention of the test classification).
The explanation is that by choosing a standard rate this allows a consistent comparison; if it takes 30 minutes for the rate to be reached for one fabric and 60 minutes for another, then the latter is clearly resisting permeation more effectively. Though neither would indicate that the suit can be safely worn for 30 or 60 minutes.
It is also worth noting that the different rates used in Europe and North America explains the occasional differences in breakthrough times reported for the same chemical against the same fabric.
What are the Implications for Chemical Protective Clothing?
There is a very clear implication; that whereas most users believe “breakthrough” means that at that point NO chemical has permeated through the fabric, in fact the chemical has already been permeating through for an unknown period…
This is best understood by considering a graph of permeation rate of a hypothetical chemical
Chemical Hazards in the Workplace: Understanding Permeation Test Breakthrough
In this graph time in minutes is on the x-axis with the permeation rate on the y-axis. The curve shows the rate of permeation over time.
This misunderstanding of permeation test data is one of many PPE myths. You can read about 10 more in our ebook below:
For safety managers dealing with chemical hazards in the workplace this could be very worrying; it means wearers of chemical suits may be coming into contact with chemicals when they have assumed they were not and that they were safe. However…
There are good reasons that this revelation – if a revelation it is – may not be the potential disaster it could be:-
- First, many chemicals are reported with a >480 minute breakthrough. In this case permeation may not have taken place at all: “First breakthrough” has not necessarily occured at all. In other words the rate could have remained at zero for 480 minutes (although you simply do not know if it has or not just from the “breakthrough” time);
- 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 a rate of less than 1.0µg/min/cm2 results in permeation of very small volumes of chemical and may not (depending on the chemical) be critical.
- Third, this analysis assumes ongoing contact of the chemical with the suit fabric. In many cases chemical safety clothing is worn to guard against the risk of contact. Often if contact occurs a user would immediately withdraw and remove the suit so ongoing permeation is irrelevant.So whilst this issue likely to be critical only in some circumstances, given the nature of many chemicals it would be high risk to assume that it is not important in all circumstances.
Why Does This Matter for Chemical Resistant Clothing?
It would be wrong and dangerous to assume that this does not matter and does not need at least to be checked. As we saw in “The Hidden Killers” there are hundreds, possibly thousands of chemicals in use on a daily basis throughout global industry, all having different properties, toxicity levels and health hazards. So it is worth repeating and highlighting four important points about chemicals and the business of managing chemical hazards in the workplace:-
- Many chemicals can be dangerous in very small volumes, causing cancers and other catastrophic health problems over an extended period. It is these chemicals for which proper understanding of permeation rate and breakthrough might be important.
- Often such chemicals have no immediate effects. If these chemicals permeate through the suit fabric and contaminate the wearer they will probably not even be aware of the contamination – and without proper analysis will probably remain unaware of it until health problems develop months or even years later.
- Commonly tasks involving hazardous chemicals in the workplace are repeated on a regular basis – perhaps even daily. If this misunderstanding of breakthrough times means users might be coming into contact with small amounts of a toxic chemical regularly it could be even more critical
- Of the thousands of chemicals in use today knowledge about the effects of many is limited. They are often “suspected” of causing cancer or “may” result in damage to internal organs. Given the number of chemicals in use it would be foolhardy to assume that because we are not aware of specific health problems they might cause right now this means there are no health problems.
“Just because a chemical is not doing immediate harm…
…does not mean it is not doing any harm”
Chemicals have different effects – often long term, often life changing or even life ending and too often only suspected or worse, unknown. And chemicals have widely differing levels of toxicity. So assuming that this misunderstanding of test “breakthrough is “not likely” to be a problem is not good enough. It could be critical… and right now too many safety managers charged with protecting workers against chemical hazards in the workplace are not even aware that the term “breakthrough” has been misinterpreted, and that the consequence could be that workers are regularly coming into contact with a chemical without anyone even being aware of it…
The first important point is to understand the chemical hazard.
- it is highly toxic and potentially harmful in small volumes, and
- its effects are only long term and contamination might go unnoticed then misunderstanding of permeation test breakthrough may well be critical…
A Health Time-Bomb?
The fact is, if you wrongly use permeation test breakthrough as a “safe-wear” time…
…or even as an indication that a chemical suit will safely protect against a chemical hazard in the workplace…
…you could be sitting on a health time bomb…
The Solution for Effective Chemical Safety
This is all very well, but it leaves an obvious question for users of chemical suits:-
“How do I know how long I am safe?”
You might be relieved to hear that there IS a solution and you can read about how to calculate safe-use times in the third of our Chemical Safety at Work blog series.
This article in the November, 2016 issue of Health and Safety International about Frank Schaaf, Head Nurse at Evonik in Antwerp is an example of an effective safety manager who understands this issue and has taken steps to address and has enhanced chemical safety on site. Frank has the answer and has been calculating safe-use times for chemical suits for years…