We're sorry, but OSHAcademy doesn't work properly without JavaScript enabled. Please turn on JavaScript or install a browser that supports Javascript.

664 HAZWOPER for General Site Workers V
Skip to main content

664 HAZWOPER for General Site Workers V

Instruments

The selection of equipment to be used must be part of the air monitoring plan.

Portable Gas Detector

There are many factors to consider when determining the proper equipment to use.

  • Hazard: The proper equipment must be selected to monitor the specific hazard or chemical.
  • Selectivity: Selectivity is the ability of an instrument to detect and measure a specific chemical. If other chemicals are detected, they are called interferences. Interferences can affect the accuracy of the instrument reading.
  • Sensitivity: Sensitivity is important when slight concentration changes can be dangerous. Sensitivity is defined as the ability of an instrument to accurately measure changes in concentration. Therefore, "sensitive" instruments can detect small changes in concentration.
  • Accuracy: Accuracy is the measure of how close readings are to true values. It is expressed as % bias. For example, if an instrument is tested and the average results are 15 % higher than the true concentration, then the instrument is said to have a bias of + 15 %. NIOSH recommends a portable direct-reading instrument be within 25 % of the true value 95 % of the time.
  • Precision: Precision is the grouping of the data points. It is a quantitative measure of the variability of a group of measurements compared to their average value. It is defined by the standard deviation. This value is a ± qualifier when a value is reported (e.g., 10± 1 ppm).
  • Calibration: An instrument must be properly calibrated, prior to use, to function properly in the field. Calibration is the process of adjusting the instrument readout so it corresponds to an actual concentration. Calibration involves checking the instrument results with a known concentration of a gas or vapor to see that the instrument gives the proper response. For example, if a combustible gas meter is checked with a calibration gas that is 20% of the lower explosive limit (LEL), then the instrument should read 20% of the LEL.
    • Instruments come from the manufacturer calibrated to a specific chemical. The manufacturer supplies information about how to maintain calibration.

Knowledge Check Choose the best answer for the question.

4-5. When is the sensitivity of air monitoring equipment important?

Previous Section
Next Section