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HMW Enterprises, Inc.
207 N. Franklin Street
PO Box 309
Waynesboro, PA 17268
Telephone (717) 765-4690
Fax (717) 765-4660
Sales@hmwent.com

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:

CLASSIFICATIONTYPICAL MATERIALS
CLASS IGASES
Those areas in which flammable gases or vapors may be present in the air in sufficient quantities to be explosive or ignitable
Group AAcetylene
Group BHydrogen and materials with similar properties
Group CDiethyl ether, ethylene, and similar substances
Group DGasoline, methane, many industrial substances
CLASS IIDUSTS
Those areas made hazardous by the presence of combustible dusts
Group EMetallic dusts and dusts with similar electrical characteristics
Group FCoal dusts, carbon black, and dust with similar electrical characteristics
Group GPlastic dusts, agricultural dusts
CLASS IIIFLYINGS
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 1DIVISION 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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