Hello land_dispute and thank you for choosing JustAnswer.
Though there has been no direct evidence of adverse effects from inhaling the waste gas from patients who have been administered isoflurane during surgery, there is a potential for harmful effects from chronic exposure. Because of this potential risk, the exposure level was established.
I hope this answered your question. If you need more information, please let me know.
I will accept you answer, even though it is not quite what I was looking for! I knew that the UK set a level of 50 ppm (http://www.hse.gov.uk/coshh/table1.pdf) but was there actually any research behind it, if so are the scientific papers on line? in the USA the ACGIH sets exposure limits based on scientific research, which OSHA eventually adopts, however isoflurane levels has not been set yet so I cannot rely on ACGIH or OSHA data. I hoped an MD familiar with the UK WEL process would answer this question, but thank you.
In the US, NIOSH sets the occupational exposure limits. They set a limit to include all halogenated compounds, even though isoflurane was not being used when the standard was set and it is metabolized differently than other compounds.
Here is a link to a 1997 study regarding isoflurane and exposure limits:
Thank you for the accept!