Which of the following is correct regarding responders using photoionization devices (PIO) at weapons of mass destruction or hazardous materials incidents?

• A. It is slow to detect hydrogen cyanide.
• B. It recognizes natural gas most readily.
• C. It does not identify the material present.
• D. It is used to detect carbon monoxide.

Answer: (C)

Photoionization devices shine by giving a quick signal about the presence and relative amount of ionizable organic vapors, but they do not tell you exactly which chemical is present. In weapons-grade or hazmat scenes, this means a PID can indicate that VOCs are in the air and show a trend (rise or fall in concentration), but it cannot identify the specific substance responsible for the reading. For identification, you’d need confirmatory methods such as GC/MS, FTIR, or targeted sampling. That’s why the statement that best fits is that the device does not identify the material present. Keep in mind that some gases (like CO) aren’t reliably detected by PIDs due to their ionization energy, and natural gas is a mixture of compounds, so a PID’s reading isn’t a definitive label for any single substance.