Can My PID Monitor Distinguish Between Multiple VOCs?

Even for people who are quite familiar with gas detection in industrial or confined space settings, there are some finer points where more explanation is necessary. A customer recently wrote with a question about his PID monitor. He wanted to know if his MultiRAE PID monitor which was set to measure Turpentine would pick up a multitude of volatile organic compounds (VOCs) or if it would only measure the specific gas.

We told him a MultiRAE monitor with a PID sensor can be set to detect Turpentine as well as a wide range of other VOCs. However, the monitor cannot differentiate between various VOCs you may have on-site. For instance, if you wish to check for jet fuel in this corner of the factory and diesel fuel on the other side, the monitor cannot distinguish between the two.

In practice, the monitor is set for the most dangerous VOC known to be present. With the MultiRAE there is a handy scroll-down menu listing all possible VOCs your PID lamp will recognize. The monitor will then go into alarm if dangerous levels of any VOCs register on the device.

He wrote back to expand on his original question: "Methyl mercaptan has the lowest 8 hr OEL/TWA (0.5ppm) compared to dimethylsulphide (10ppm) or turpentine (20ppm). If the MultiRAE is showing 4ppm then I should also have a device that can detect only Mercaptan if I want to be able to rule out mercaptan as a potential hazard in the area, would you agree?"

Indeed we would agree. Portable monitors aren’t going to allow you to rule out mercaptan in an area. In fact, the only way to know exactly which VOCs are in an area is to do an air test with an industrial hygienist. They can come take an air sample, or these days just send you a kit in the mail along with instructions. The sample is sent to the lab and a thorough analysis can be made to let you know exactly what VOCs are in the area. While there are some devices that have the sensitivity to measure only a specific VOC like mercaptan, they are specialty devices and not produced currently as hand-held devices.

Another point to be aware of, the MultiRAE is only able to measure mercaptan down to 1.0 for OEL/TWA, and not to the NIOSH standard of 0.5.

If you have questions or need help finding the right gas detection solution for your application, please feel free to call us at 800-829-9580, or visit us online at pksafety.com.