Hazardous Area Computers
Introduction
Government and industrial organizations concerned with matters of safety impose very strict regulations on the operation of computers and other electrical devices placed in hazardous environments. Consequently, strict rules and precise specifications control the proper construction and installation of these devices. Often, these rules and regulations frustrate the engineer, since they limit the scope of project requirements. It is not only the " bits and bytes" that define a hazardous area project, but also the mandates and interests of groups and organizations such as OSHA, insurance companies, corporate legal departments, and others.
Hazardous areas have been classified according to the following table:
| CLASSIFICATION | TYPICAL MATERIALS |
|---|
| CLASS I | GASES |
|---|
| Those areas in which flammable gases or vapors may be present in the air in sufficient quantities to be explosive or ignitable |
| Group A | Acetylene |
| Group B | Hydrogen and materials with similar properties |
| Group C | Diethyl ether, ethylene, and similar substances |
| Group D | Gasoline, methane, many industrial substances |
| CLASS II | DUSTS |
| Those areas made hazardous by the presence of combustible dusts |
| Group E | Metallic dusts and dusts with similar electrical characteristics |
| Group F | Coal dusts, carbon black, and dust with similar electrical characteristics |
| Group G | Plastic dusts, agricultural dusts |
| CLASS III | FLYINGS |
| Those areas in which there are easily ignitable fibers or flyings present due to the type of material being handled, stored or processed. These may include rayon, cotton, sisal, hemp jute, Spanish moss, and similar substances |
| DIVISION 1 | DIVISION 2 |
|---|
| A location in which ignitable concentrations of the combustible material(s) are present in the air under normal operating conditions. | A location in which ignitable concentrations of the combustible material(s) are present in the air only under abnormal operating conditions, such as the case during accidental rupture or breakage, or during unusual or faulty operations. |
In the USA, agencies such as UL (Underwriters Laboratories), FMR (Factory Mutual Research) and others perform qualification tests and certify equipment for operation in various sectors of a given hazardous area location. International agencies, like CSA (Canadian Standards Association), BASEEFA (British Approvals Service for Electrical Equipment in Flammable Atmospheres), CENELEC (European Committee for Electrotechnical Standardization) and others in Europe concern themselves with Certification issues outside the USA. Certification of hazardous area equipment is costly and time consuming, and once certified, any change or modification requires re-certification.
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