Rationale for Classification of Combustible Gases, Vapors, and Dusts with Reference to the National Electrical Code

摘要

Electrical equipment that operates in an environment containing combustible materials must conform to requirements presented in Article 500 of the National Fire Protection Association's National Electrical Code (NEC). These requirements reflect the degree of combustion hazard created by the particular chemical compounds present in the equipment environment, and compounds are classified in groups that are indicative of the perceived explosion hazards. The Committee on Evaluation of Industrial Hazards of the National Research Council's National Materials Advisory Board has classified many hundreds of compounds in accordance with current NEC groupings. Although some tests were conducted on selected key compounds, the committee primarily considered the chemical similarity of compounds and other known flammability properties and relied heavily on the experience and intuition of its members. The committee also has recommended that the NEC grouping of dusts be changed in some ways and has reclassified dusts according to the modified version of the code. Nevertheless, the committee has serious reservations about the entire classification procedure and the precepts on which it is based, and these are discussed in this report.