Rank: Forum user 
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Hi I have been asked to carry out a Coshh assessment for a new substance we have introduced. I have obtained the safety data sheet but how do I establish the Short Term Exposure Limits and Long Term Exposure Limits from their figures. They have said STEL 1080 mg/m3, 250ppm and LTEL 430 mg/m3, 100ppm how do I convert these figures to an actual time period without air monitoring equipment? Thanks
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Rank: Forum user
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I think that you can't.
I often get asked to write COSHH Assessment for people who want to use a certain substance for a work project but don't know how to meet STEL and LTEL. My usual reply is to ask them to explain to me how they know it's safe to use the substance, if I can't measure it.
Surely the people who are responsible for designing the work process that require particular substances are also those who take responsibiity for ensuring there is sufficient budget to supply you with the correct monitoring equipment, if the budget isn't there, then they've failed to plan the project properly, you can't magic an answer.
On the other hand there is 'reasonableness' to consider. If it's just a pot of paint to re-paint a desk you could follow the written instruction on the tin "Only use in a well ventilated area"?
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Rank: Super forum user 
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These limits are quite high. If the process doesn't entail emitting lots of the stuff into the air that people are breathing then you won't get anywhere near them.
So either show that hardly any is going to be emitted into the air that people are breathing (because it's contained, it's not at a temperature at which lots of vapour comes off it, there's ventilation, etc) or show that lots is going to be emitted and propose control measures to reduce it. COSHH Essentials on the HSE website illustrates how to decide based on the vapour pressure and process temperature.
Air monitoring isn't automatically needed for a COSHH assessment. You're more likely to need it when the limits are very low so that even if the control measures are stringent you still can't conclude that they are good enough.
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