Evaluation of Systems for Intrinsic Safety

  • Ernest C. Magison


Evaluation of a system, i.e., equipment and associated wiring, to determine whether it is intrinsically safe in accordance with the requirements of ISA Recommended Practice RP12.2, is not, and cannot be, a “cookbook” procedure. ISA RP12.2 adequately states the essential energy limitations and specifies the considerations of failure against which to judge the system. However, it is not practical to list all possible specific constructional features which would render a particular mode of failure highly improbable or “for all practical purposes” impossible. The requirements of RP12.2 must be applied to a particular system with judgment. This judgment must be based on knowledge of the technology underlying the specific requirements of RP12.2. This is emphasized in RP12.2, paragraph 2.4:

“This Recommended Practice is intended to promote uniformity among specialists. It is intended that it be applied only by those who have carefully studied the subject. This Recommended Practice is not an instruction manual for untrained persons.”


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  1. 1.
    Proceedings of 1960 Symposium on Safety for Electrical Istrumentation in Hazardous Areas, Instrument Society of America, Pittsburgh. Maltby, F. L., “History of ISA Committee on Hazardous Area Instrumentation.” Hickes, W. F., “Intrinsic Safety.”Google Scholar
  2. 2.
    “A Review of Electrical Research and Testing with Regard to Flameproof Enclosure and Intrinsic Safety of Electrical Apparatus and Circuits, “Ministry of Fuel and Power, 1943, London.Google Scholar
  3. 3.
    National Electrical Code, Article 500.Google Scholar
  4. 4.
    British Standard 2031, “Metal Rectifiers for Intrinsically Safe Signaling and Control Circuits. “Google Scholar
  5. 5.
    British Standard 1259:1958, “Intrinsically Safe Electrical Apparatus and Circuits.”Google Scholar
  6. 6.
    British Standard 1975:1953, “Primary Cells and Batteries for Intrinsically Safe Bell Signaling Circuits in Coal Mines.”Google Scholar
  7. 7.
    British Standard 1538:1949, “Intrinsically-Safe Transformers for Bell-Signaling Circuits.”Google Scholar
  8. 8.
    British Standard Code of Practice CP 1003:1948, “Installation and Maintenance of Flameproof and Intrinsically-Safe Electrical Equipment.”Google Scholar
  9. 9.
    Ministry of Fuel and Power Testing Memorandum No. 10, “Test and Certification of Intrinsically Safe Electrical Apparatus and Circuits.”Google Scholar
  10. 10.
    IEE Conference Report Series No. 3, “Flameproofing, Intrinsic Safety, and Other Safeguards in Electrical Instrument Practice,” April 27, 1962. Berz, I., “Protective Devices for Intrinsically Safe AC Circuits.” Haig, Lister, and Gordon, “The Testing of Flameproof and Intrinsically Safe Electrical Apparatus.” Redding, R. J., “Intrinsic Safety Practice in Industrial Instrumentation.” Thomas, V.M., “The Design of Intrinsically Safe Apparatus for Use in Coal Mines: A Review of Data and Technique.” Wells, G.M., “Intrinsically Safe Instrumentation in Coal Mining.” Simons, Kögeler, and Bijl, “Safety of Electrical Instruments in the Oil Industry.”Google Scholar

Copyright information

© Springer Science+Business Media New York 1966

Authors and Affiliations

  • Ernest C. Magison
    • 1
  1. 1.Honeywell Inc.Fort WashingtonUSA

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