For a vapor such as hydrogen peroxide, which has an OSHA permissible exposure limit (PEL) of 1 ppm (8 hr TWA), the DAQ has an 8 hour TWA of 1 ppm. There is no OSHA short term exposure limit for hydrogen peroxide and so the DAQ does not have a STEL alarm.
For vapors such as peracetic acid for which there are no OSHA PELs, alternative exposure limits must be sought. The first step is look to see if there are any ACGIH threshold limit values (TLV) or other recognized exposure standard. The ACGIH does not have a TLV for peracetic acid, but it has proposed a short term exposure limit (STEL) of 0.4 ppm. In the absence of recognized exposure limits, one looks for published studies and reviews of published studies.
Recently Pechacek, Maier and Haber reviewed a range of studies of the health effects of exposure to peracetic acid and came up with several recommendations. The authors are with Ecolab, one of the largest suppliers of peracetic acid and TERA, a non-profit organization dedicated to solving problems associated with public health.
The authors' first recommendation is that neither a ceiling limit nor a STEL on its own is appropriate since
" PAA is an irritant that can cause cytotoxicity. Insufficient dose-response information is available to ensure that the absence of a sensory response also protects from accumulating subclinical cytotoxic responses." The authors go on to comment that the combination of 8 hr TWA and STEL is valuable. This conclusion may have significance to the ACGIH proposed STEL for peracetic acid.
In addition to recommending the use of both an 8 hr TWA and STEL, Pechacek et al calculated a value for the 8 hr TWA occupational exposure limit based on published reports of 0.26 to 1.56 mg/m3, which corresponds to a concentration range of 0.08 to 0.5 ppm.
The ChemDAQ DAQ calculates both the STEL and the 8 hour TWA, and the ChemDAQ alarm limits are set at 0.4 and 0.2 ppm respectively, both within the range recommended by Pechacek, Maier and Haber.