Photoionization detectors (PIDs) at hazardous materials incidents provide which of the following?

• A. They detect carbon monoxide.
• B. They identify the exact material present.
• C. They are slow to detect hydrogen cyanide.
• D. They do not identify the material present.

Answer: (D)

Photoionization detectors measure the presence and level of volatile organic compounds by using ultraviolet light to ionize many organic molecules. The reading reflects the total VOC concentration in the air, not the exact chemical identities. Because a PID doesn’t produce a fingerprint for a specific substance, it cannot tell you which material is present. To identify the exact chemical, you’d need sampling and laboratory analysis (or more specialized instrumentation). PIDs are fast and useful for spotting VOCs and tracking changes, but they do not identify the material present.