PID (photoionization detectors) are generally used for the detection of volatile compounds and certain classes of toxics. They've been around for awhile, and are generally included in every HAZMAT team's toolkit.
There has been some controversy over the impact that humidity has on their readings, with one company- Ion Science- claiming that humidity variations have a significant effect on detection suppression. In high humidity environments that claim this suppression could be in excess of 50%, which makes humidity and serious consideration when trying to get an accurate reading out of a PID. However, there are rumors of a new study showing that improvements in PID technology have knocked that down to the range of only 10%.
Of more concern to me is the effect of smoke on PID readings at the time of an emergency event and residual contamination on the detector cell because of the smoke and/or chemical extinguisher vapors. In earlier postings I have stressed the importance of cleaning PID cells after a chemical event. Now I raise the question of how much smoke or other particulate and/or condensate fumes have on the accuracy of a PID's readout.
To my knowledge, there have been no studies conducted on this issue by any of the gas detection companies or sensor manufactuerers. I'm going to keep pushing them to look at this problem, and hope you'll push for the same. This problem shouldn't be ignored. After all, the responders actually are at risk in the field. Gas detector salesman typically don't tend to show up at emergency events where toxic gases are involved.