I would advise that this may prompt them to seek the advice of a competent person and they might not need to understand the sampling methods involved?
Surely the % under a WEL is irrelevant, the HSE state that the WEL sets a point at above which the substance may present a risk to health. So if you are below it, surely you are below it and demonstrating adequate control (unless of course it's an asthmagen, sensitiser or carcinogen)
Why would the poster need to be trained in taking measurements?
I agree a CoSHH assessment needs to be completed by a competent person but that was not the original question... lets keep it on topic.
Fair comment that it may prompt going to a competent person.
air-sampling is not an exact science, confounding factors, expected and unexpected sampling errors, normal variation in time, tasks, environmental conditions, etc. mean that any one sample is only part of distribution curve (usually log). We worked, as a general rule of thumb, that any measurement above 30% of WEL requires a statistically significant number of samples to demonstrate that workers health was not unduly put at risk. The 30% rule varied if the level of hazard so required.
Agreed that no training in sampling needed if someone else does it, I was pointing out that "COSHH training" wouldn't be enough to deal with the sampling raised by other posters.
The poster asked how they should interpret the figures for each substance - "On topic" is an explanation of why interpreting EH40 and using it in the workplace is not simple. another poster pointed out the samping is needed for the figures to be meaningful.