On-Site Use of Direct-Reading Instruments

Unlike air sampling devices, which are used to collect air samples for later analysis in a specially equipped lab, direct-reading instruments provide immediate information at the time of testing. They are the primary tools of initial site characterization of air quality. They have both benefits and limitations.

Benefits

• Direct-reading instruments can rapidly detect flammable or explosive atmospheres, oxygen deficiency, certain gases and vapors, and ionizing radiation.
• Information provided by direct-reading instruments can be used to do the following:
  • Take appropriate protective measures (for example, PPE or evacuation)
  • Determine appropriate equipment for further monitoring
  • Determine best procedures for further sampling and analysis

Limitations

• Only specific classes of chemicals can be detected and/or measured by direct-reading instruments.
• Only certain concentrations of airborne contaminants can be detected or measured (generally, direct-reading instruments are not designed to measure or detect airborne concentrations below 1 ppm)
• Many direct-reading instruments that have been designed to detect one particular substance also detect other substances (interference) and consequently may give false readings.

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