What does PID stand for in gas detection?

• A. Portable Infrared Detector
• B. Photonic Ionization Device
• C. Photoionization Detector
• D. Positive Ion Detector

Answer: (C)

Photoionization Detector is what PID stands for in gas detection. It works by exposing the air sample to ultraviolet light, which has enough energy to ionize many volatile organic compounds. The ionized molecules and free electrons are collected by electrodes, producing a small current that is proportional to the concentration of ionizable vapors in the air. This allows for rapid, sensitive screening of a wide range of VOCs at very low levels, which is why PIDs are commonly used in hazmat and industrial hygiene settings. Readings are usually reported on a VOC scale and calibrated with a reference gas like isobutylene, rather than providing an exact concentration for each individual compound. The device will not reliably detect inorganic gases or substances with ionization energies beyond the lamp’s energy, and humidity can sometimes affect responses. The other options describe different detection methods or terms that don’t match the UV photoionization principle of this instrument.