Is the reported ppm based on a TWA?
The concentration (ppm or mg/cubic meter) on the laboratory report is the time-weighted average concentration for the actual exposure time that was used. It is not based on an 8 hour period, unless the actual exposure time is 8 hours. There are exceptions to this, when the client requests the results for an 8 hour TWA period, or when it will add to the clarity of the report, as described below.
