Which of the following is an example of a passive detector?

• A. Multi-gas meter
• B. Colorimetric detector tube
• C. Photoionization detector (PID)
• D. Infrared gas analyzer

Answer: (B)

A colorimetric detector tube is an example of a passive detector because it relies on a chemical reaction that occurs as a result of gas exposure without the need for active sampling systems or powered devices. In this method, a sample of air is drawn through the tube passive by diffusion. The chemical reagents inside the tube react with specific gases to cause a color change, which indicates the presence and concentration of those gases. This makes it useful for field assessments where equipment may be limited or where continuous monitoring isn't needed.

In contrast, devices like a multi-gas meter, photoionization detector, and infrared gas analyzer require active mechanisms to function. These devices often employ pumps or other electrical components to collect air samples or analyze gas concentrations, thus classifying them as active detectors. Understanding the distinction between passive and active detection methods is crucial for choosing the appropriate equipment based on the situation, including factors like portability, power availability, and the need for continuous monitoring.