I have a question about using Expostats for evaluating compliance with a ceiling limit. Do I change the “Overexposure risk threshold” to “0” for a ceiling OEL?
Also, under the Tool1 “Exceedance” tab, do I change the “Exceedance threshold” also? – obviously it can’t be “0” but should I use 1/250 (i.e., 1 day out of 250 working days per year; or 1 day out of a working life – 10,000 days)?
Should I change anything else?
For a ceiling limit, presumably we want the proportion of exposures above the OEL as low as possible. Not zero indeed as it is not possible to demonstrate this without measuring all situations. Your proposal of 1/250 is as good as any.
Then Expostats is going to estimate overexposure risk, i.e. the probability that this threshold is breached, i.e. that more than 1/250 days are over the OEL.
Overexposure risk threshold is the maximum acceptable value for this probability, i.e. what probability of a problem is too high. Traditionnally this is 5% ( equivalent of 95% sure that there is no problem), but a European guideline proposes 30%.
To summarize the Expostats speedometer : overexposure risk drives the needle , and overexposure risk threshold defines the colors.
One consideration if you are analysing real time data : carefull that they are not too correlated (e.g. a continuous 2h series of 1 min measurements), which would mess the inference.
I hope this helps