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How Long Am I Safe?

Safe-use times for chemical protective coveralls

Frank Schaaf is Head Nurse at Evonik’s multi-user site in Antwerp. His approach to calculating safe-use times for coveralls used for protection against chemicals on site brings a level of understanding to an issue commonly misinterpreted in the industry, which deserves consideration by anyone involved in hazardous chemical protection.

Antwerp knows all about diamonds. It’s the rarity and the fact you have to dig through a lot of rock to find it that makes a diamond so valuable. Frank Schaaf is a similar rarity worth finding. With 25 years under his belt at Evonik in Antwerp, the last 10 of which as Head Nurse leading the team of medical staff charged with both the selection of PPE and the ongoing monitoring of more than 1,000 on-site employees, safety is both his profession and his passion. His experience in the field extends even beyond that: four years’ study at an Antwerp medical school; two years combining home-care with driving an ambulance; not to mention a one-year stint in the Belgian Army Medical Corps. For some such a long career might lead to a cynical weariness of the subject, but not Frank. The enthusiasm with which he discusses his role is evident, and with that wealth of knowledge and expertise he can speak with some authority on the subject of managing safety on a modern chemical production site. His impeccable credibility in the field is topped off with an infectious mix of knowledge, experience and enthusiasm.

In the compact but well equipped Health Centre at the Evonik site in Antwerp, Frank’s approach to the calculation of safe-use times for suits used to protect against hazardous chemicals was a revelation. He smiled at the memories of how things were when he joined the company in 1990, saying: “When I started with Evonik smoking was allowed in the offices - and even in the canteen! There was just one type of chemical suit on site for all applications and I think just three types of gloves - things have moved on a lot since then.”

And quite right too. Frank’s job now entails a complex combination of tasks focussed on maintaining the health and wellbeing of his charges: not only the regular on-site employees, but also those about to travel to (or having returned from) other Evonik sites around the world. It’s a serious business. Not only is Frank closely involved with the selection of on-site PPE, but also with regular health monitoring of all employees, including a variety of regular check-ups: annual blood tests, electro-cardiographs, eye tests, hearing tests and fitness tests – multiply all those by over 1,000 employees and you realise it is no small matter.

Prioritising safety

This reflects the corporate attitude of Evonik to the issue of employee safety. On a site that can have up to 350 chemicals in use, safety is priority number one and the uncompromising objective of the company’s policy is zero accidents. The “Safety at Evonik Programme” encourages employees to ask “am I safe if I do this job?” and if they think the answer is no each has the authority to choose not to do it until their safety issues are addressed. The aim is to encourage and enable a mind-set that anticipates what can go wrong and places the final responsibility for safety firmly in the hands of individual employees. Prevention is definitely better than cure.

Another major aspect of Frank’s job is supporting site managers to conduct risk-assessments for any task or operation involving hazardous chemicals. This includes assessing the effectiveness of chemical suit options against the chemicals in use.

Selecting chemical suits

Frank has a four-stage approach to the selection of a chemical suit for a specific task. This consists of:

  1. What chemicals are involved? Are they in a closed circuit system, i.e. no or little risk of contamination? What is the risk of contamination?
  2. Is the risk of contact routine/ inevitable? Or will contact only occur if there is an error or an equipment fault, such as a spilt valve or pipe?
  3. How long is any contamination of a suit likely to last?
  4. What is the suitability of existing on-site suit options for protection against the chemical in question, i.e. how long can a suit be used to protect against that chemical before harm may occur?


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This is not an exhaustive list of questions or issues for every occasion of course – that’s the point of a risk assessment. But it is this final part - assessing the suitability of a suit for protection against a specific chemical – in other words, for the user answering the question “How long am I safe?” – is perhaps both the most critical and the most problematic to answer. It is also the part to which Frank brings a refreshingly logical and knowledgeable approach.

Safe use times

In many cases the process starts with a regular question from site managers to which Frank must provide an answer: “How long can we safely wear this suit to protect against this chemical?”

Many in the industry simply use a manufacturer-supplied permeation test breakthrough to answer this question, but Frank understands it is not as simple as that. He said: “I always understood that a permeation test “breakthrough” result is not about how long the suit will protect against a chemical. It’s fine for comparing different fabric performance, but is nothing to do with how long you are safe in the suit. So when I contact manufacturers for permeation test data I’m not especially interested in the “breakthrough”. I want to know the actual recorded permeation rate. With that information I can calculate the volumes of chemical likely to permeate over time and compare it to the level of toxicity associated with that chemical. Only that process can give us an idea of safe-use time how long an operator can use a suit before he risks reaching a hazardous level of contamination.”

The process might take anything from a couple of days to several weeks. The first task is to access the test information available from the suit manufacturer. If a test against the required chemical has already been done, and if the assessed permeation rate is available then that might shorten the time considerably. If not, then it might be weeks before a test can be conducted. However, once the permeation rate is provided, Frank can then go through a series of calculations which conclude with being able to advise the site manager how long the suit can be worn safely.

Frank said: “It’s less complex than it sounds. It’s basically a process of multiplying the permeation rate by the area contaminated and the duration of the exposure. Of course that does mean making certain assumptions about the last two, but for safety its best to assume the worst – assume the contaminated area will be large and that the duration of exposure will be longer than expected. You are then building in a safety margin, which is no bad thing when we could be talking about people’s health – maybe even their lives!”

Having calculated a volume permeated its then simply a case of looking at the toxicity level of the specific chemical, which is available from various sources. That tells you what volume of the chemical might be sufficient to cause any harm.

Frank added: “Using this method I can calculate a table of “safe-use” times based on various exposure times and situations. So I can provide the manager with an answer to his original question - a guide to how long that suit can be used safely to protect against that chemical. But it’s no use to only look at the permeation test breakthrough. The reality is that tells you nothing at all about safe-use time”.

Impact of temperature

It isn’t, however, a perfect solution. One major issue is temperature. The fact is temperature has an effect on permeation; the higher the temperature the faster permeation is likely to occur. The problem in incorporating temperature into Frank’s calculation is that the information is simply not available. Because the permeation test is designed for the purpose of fabric comparison (the test standard actually states this), to ensure consistency the standard requires that test samples are preconditioned for 24 hours at a temperature of 23°C; all permeation testing is conducted with fabric thus preconditioned. Which means no information on permeation rates at higher (or lower) temperatures is available from a permeation test.

“Being unable to account for temperature is a great concern” said Frank, “but there is little can be done about it. The information is simply not there from test reports and it would be impractical to have tests done at lots of different temperatures. It is possible to make assumptions about how permeation rate will increase with temperature, but it’s difficult to be accurate, which is another good reason to build in wide safety margins to the calculations”.

All this has now been made much easier by the availability of an on-line app which essentially allows calculation of permeation rates and volumes permeated compared with chemical toxicity. This is possible because permeation is a well understood physical process that is entirely predictable provided you know the molecular structure of the specific chemical and the polymers in the barrier fabric that is trying to prevent it permeating. Further, it also incorporates different temperatures into the calculation so the higher permeation rate that a higher temperature might bring about can now be accounted for.

Frank said: “I still like to also look at physical test data and ensure there are no major differences in permeation rates. It’s a good built in safety margin which is good practice. But being able to take into account temperature is a big step forward. I’ve now been able to provide our on-site managers with complete tables of ‘safe-use’ times at different exposure levels and different temperatures for most of the chemicals we have on site.”


The fact is that throughout the global safety industry many users and managers involved in chemical protection believe that they already have a “safe-use” time provided by the normalised breakthrough in a permeation test. Even manufacturers commonly offer test “breakthrough” as if it is tantamount to a safe-use time. It is commonly believed that “>480 minutes” from a permeation test means precisely this, that you are safe for more than 480 minutes. It is a sobering realisation for many users that it does not mean this at all and that at the point of test “breakthrough” the chemical might already have been permeating through the fabric for some time.

Frank Schaaf at Evonik is leading the way not only in demonstrating understanding of this, but also with a method of calculating a “Safe-Use” time which uses the information correctly to calculate how long a suit can safely be used.

Of course this method of calculating safe-use times for chemical suits against specific chemicals – whether done manually as Frank has done or using a molecular modelling tool is not a complete fail-safe. At the very least, however, it is a method that uses the available information appropriately and moves considerably closer to an understanding of how long a chemical suit can be safely used against a chemical. Finally we’re moving closer to an answer to that key question, “How Long am I Safe?” that is based on reality rather than assumptions.

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Frank Schaaf is Head Nurse at Evonik’s multi-user site in Antwerp.