PID Measurements Vs Air Samples

Is your photoionization detector (PID) keeping your workers safe? What do you set your alarm levels to?

If your company uses a PID to protect workers from exposure to Volatile Organic Compounds (VOCs), are they really protected? A PID is a non-specific tool for measuring levels of VOCs in air. It displays the total sum of all detected compounds ionized by the internal lamp. Other PIDs use solid state sensor technology, which have limitations as well. In Ontario, there is no MOL exposure limit for Total VOC (TVOC). Ont. Reg. 833 lists several VOCs with individual exposure limits, many of these in ppm or mg/m3.

So how do you compare the PID readings to these individual limits? The short answer is, you really can’t. The only verifiable way to determine specific VOC concentrations is by collecting an air sample and having it analysed at a certified laboratory. Airzone can assist companies with VOC sampling and analysis and determine the exact compounds in the air. Our integrative sampling results are directly comparable to the 8 hour Time Weighted Average listed in the regulation.

Overall a PID is most useful as an investigative tool to determine if a liquid is volatile or if VOCs are present in an atmosphere. However they do not unambiguously determine which compounds are present at what concentration. Therefore a worker’s exposure remains unknown.