This paper describes three distinct steps for the assessment and management of deflagration hazards associated with combustible solids, flammable and combustible liquids, and flammable gases in chemical processes. This includes rapid combustion in the form of explosion or flash-fire.
Gases, vapors, and dusts can all form flammable atmospheres under certain process operating conditions; both normal and abnormal. For many years, hazardous area classification procedures have been used to select and install suitable electrical equipment in flammable atmospheres to ensure that the electrical equipment does not become a source of ignition to the identified flammable atmosphere. The same hazardous area classification approach may be used to identify areas where ignitable atmospheres could be present under both normal and abnormal processing conditions. However, the broader objective for risk management of deflagration hazards is to expand the hazardous area classification to include all ignition sources that would be capable of igniting the atmosphere of concern and not just electrical equipment and devices.
Per NFPA 70; NFPA 497; and NFPA 499 (the National Electrical Code) hazardous locations are identified by Classes and Groups that distinguish between different types of flammable atmospheres (Class I for gases and vapors, Class II for dusts, and Class III for fibers and flyings) and the fuel properties (Group A, B, C, D, E, F, or G designation). The hazardous locations are further divided into Divisions (or Zones in international classification approach), based on the likelihood of the fuel being present. Continuous exposure within a given area to a flammable substance would require a Division 1 classification, for example, and areas where the flammable atmosphere could occur due to an abnormal condition or component failure are classified as Division 2.
