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Direct-Reading Instruments

Direct-reading instruments are valuable tools for detecting and measuring worker exposure to gases, vapors, aerosols, and fine particulates suspended in air. These instruments permit real-time or near real-time measurements, and their use is specifically required by some OSHA standards. There are many types of instruments available, each of which is designed for a specific monitoring purpose. Proper operation of direct-reading instruments is essential to ensure that accurate information is obtained when evaluating air contaminants.

Direct-reading instruments are addressed in specific standards for the general industry, shipyard employment, and the construction industry.

OSHA Standards

This section highlights OSHA standards, standard interpretations (official letters of interpretation of the standards), and other resources related to direct-reading instruments in the workplace.

Note: Twenty-five states, Puerto Rico and the Virgin Islands have OSHA-approved State Plans and have adopted their own standards and enforcement policies. For the most part, these States adopt standards that are identical to Federal OSHA. However, some States have adopted different standards applicable to this topic or may have different enforcement policies.

         General Industry (29 CFR 1910)

  • 1910 Subpart H, Hazardous materials [related topic page]
    • 1910.120, Hazardous waste operations and emergency response. Direct-reading instruments are an important element of the monitoring program outlined by this standard. [related topic page]
  • 1910 Subpart J, General environmental controls
    • 1910.146, Permit-required confined spaces. Confined spaces must be tested before entry with a direct-reading instrument for oxygen content, flammable gases and vapors, and toxic contaminants. [related topic page]
  • 1910 Subpart R, Special industries
    • 1910.269, Electric power generation, transmission, and distribution. Direct-reading instruments are required to test for oxygen-deficient atmospheres and flammable gases and vapors. [related topic page]
    • 1910.272, Grain handling facilities. Requires that the atmospheres of bins, silos, and tanks are tested before entry. [related topic page]
      • Appendix A, Grain handling facilities. It specifically states that direct-reading instruments should be used to periodically monitor atmospheres in bins, silos, and tanks.

Shipyard Employment (29 CFR 1915)

  • 1915 Subpart B, Confined and enclosed spaces and other dangerous atmospheres
    • 1915.12, Precautions and the order of testing before entering confined and enclosed spaces and other dangerous atmospheres. Includes similar requirements to 29 CFR 1910.146.

Construction Industry (29 CFR 1926)

  • 1926 Subpart D, Occupational health and environmental controls
    • 1926.65, Hazardous waste operations and emergency response. Contains requirements identical to 29 CFR 1910.120 regarding direct-reading instruments used in construction.

Standard Interpretations

Other Resources


The following references provide information regarding methods and means used to evaluate workplace exposures with direct-reading instruments.

Sampling and Analysis

Video Exposure Monitoring (VEM)

With this technique, worker exposures are monitored with direct-reading instruments while workplace activities are simultaneously recorded on videotape.

Additional Information


Other Resources

  • The Industrial Environment - its Evaluation and Control. US Department of Health and Human Services (DHHS), National Institute for Occupational Safety and Health (NIOSH) Publication No. 74-117, (1973).

  • American Industrial Hygiene Association (AIHA). American Industrial Hygiene Association (AIHA). Publishes manuals on the use of direct-reading instruments.
    • Aerosol Science for Industrial Hygienists. Publication No. 246-SI-96R, (1995). Includes information on direct-reading monitoring for workplace aerosols.
    • Direct-Reading Instrumental Methods for Gases, Vapors, and Aerosols. In: The Occupational Environment - its Evaluation and Control. Todd LA, editor. Chapter 9. Publication No. 252-BP-97, 1997.
    • Direct-Reading Colorimetric Indicator Tubes Manual, Second Edition. Publication No. 172-SI-93, (1993).
    • Manual of Recommended Practice for Combustible Gas Indicators and Portable Direct-Reading Hydrocarbon Detectors, Second Edition. Publication No. 158-SI-93, (1993).
    • Manual of Recommended Practice for Portable Direct-Reading Carbon Monoxide Indicators. Publication No. 175-SI-85, (1985).
  • American Conference of Governmental Industrial Hygienists (ACGIH)
    • Air Sampling Instruments, 9th ed. Publication No. 0031, (2001). Includes information on several types of direct-reading instruments.
    • EPA Training Manual #7 - Emergency Response to Hazardous Material Incidents. Publication No. 3115 (EPA Manual 165.16). Includes information on using direct-reading instruments for evaluating and mitigating the release of hazardous materials.
  • National Safety Council (NSC)
    • Direct-Reading Instruments for Gases, Vapors, and Particulates. In: Fundamentals of Industrial Hygiene. 5th ed. Hahne RM, editor. Chapter 17. Product No. 15148-0000, 2002.

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