Is it really necessary to memorise exposure limits?

Many years ago, on the day I started work, after my new boss had run through the company induction, shown me around the department and told me as much as he could think of about the mysterious world of occupational hygiene I’d just joined, he’d clearly had run out of ideas about what to do with me. So he gave me a copy of the current list of occupational exposure limits (in those days HSE used to reproduce the American TLVs^®*) and told me to read through it. Looking at the long list of substances I remember asking him whether I was expected to learn them. “Of course not!” was his answer. “You can always look up a limit if you need it”. What he wanted me to do was to read through the accompanying explanatory material so that I would understand what the limits were, their legal status and how to apply them.

Given that there are several hundred limits it would be a nonsense trying to memorise them. Although as an A4 publication the HSE’s list of Workplace Exposure limits, EH40, is too big to fit in your pocket (the TLV list is much handier and pocket sized), it’s easy enough to keep in your briefcase or kit bag. Even if you leave it in the office, it generally wouldn’t take too long to find the limit you need in most cases.

These days it’s even easier to check the list as EH40 is now published online by the HSE  and can be downloaded as a pdf file here free of charge. I keep copies on my laptop and on my phone so I can consult it whenever I need to.

Of course, most hygienists over the course of time will tend to memorise some limits – for substances they come across regularly. Even then it can be dangerous to rely on memory. Limits can change and you can find yourself quoting an out-dated limit if you’re not careful. Which could lead to misinterpretation of sampling results and inappropriate advice on controls if you don’t double check the limits first.

*TLVs® – the Threshold Limit Values published by the American Conference of Governmental Industrial Hygienists