Name two devices used for direct-reading measurements of gases or vapors.

Name two devices used for direct-reading measurements of gases or vapors.

• A. Gas chromatography and mass spectrometry
• B. Photoionization detector (PID) and electrochemical gas detectors
• C. Infrared spectrometry and photoacoustic sensors
• D. Colorimetric badges and diffusion tubes

Answer: (B)

Direct-reading monitors give an immediate concentration in the field, allowing quick decisions and alarms. For gases and vapors, two common devices used for this purpose are a photoionization detector and electrochemical gas detectors. A photoionization detector uses UV light to ionize many organic compounds; the resulting current is proportional to the total VOC concentration, providing real-time readings and a rapid response to changes. It’s versatile for screening and leak detection, though it generally measures a broad class of organics rather than identifying each one. An electrochemical detector produces a current that matches the concentration of a specific gas; these sensors are highly selective, compact, and reliable for real-time readings and alarms for gases such as CO, H2S, chlorine, or oxygen-related conditions. They’re particularly cost-effective for routine occupational hygiene monitoring. Other options aren’t direct-reading field devices in the same sense: gas chromatography and mass spectrometry require lab analysis and aren’t real-time field monitors; colorimetric badges and diffusion tubes are passive sampling methods that need lab analysis after exposure periods.

Direct-reading monitors give an immediate concentration in the field, allowing quick decisions and alarms. For gases and vapors, two common devices used for this purpose are a photoionization detector and electrochemical gas detectors. A photoionization detector uses UV light to ionize many organic compounds; the resulting current is proportional to the total VOC concentration, providing real-time readings and a rapid response to changes. It’s versatile for screening and leak detection, though it generally measures a broad class of organics rather than identifying each one. An electrochemical detector produces a current that matches the concentration of a specific gas; these sensors are highly selective, compact, and reliable for real-time readings and alarms for gases such as CO, H2S, chlorine, or oxygen-related conditions. They’re particularly cost-effective for routine occupational hygiene monitoring.

Other options aren’t direct-reading field devices in the same sense: gas chromatography and mass spectrometry require lab analysis and aren’t real-time field monitors; colorimetric badges and diffusion tubes are passive sampling methods that need lab analysis after exposure periods.