Electrical Apparatus magazine, November 2003 Applying Motors in Hazardous Areas -- What are the Rules?

Where explosive gas or combustible dust may be present, a motor must be designed to minimize the possibility of fire or explosion. Such construction is costly, and economically justified only for locations that are clearly hazardous during normal circumstances. (Motor starting has been considered an abnormal condition because of its short, infrequent duration.)

In the United States, judging area classification according to the degree of hazard is the responsibility of the authority enforcing the applicable safety code, and is the subject of several standards of the National Fire Protection Association (which also issues the National Electrical Code defining the requirements for apparatus to be used in hazardous areas).

Areas of potential hazard are divided into two Classes (flammable vapors and gases, or combustible dusts). Each is subdivided into either two Divisions (1 and 2) or three Zones (0, 1, and 2. In Division 1, motors must be designed for explosion-proof or dust-ignition-proof service.

The Zone concept, standard in Europe, was adopted by the NEC in 1996 as an alternative to Divisions. Zone 0 involves such a high risk that only intrinsically safe equipment is permitted (no motors qualify).

In Class I Zone 1 locations, "increased safety" motors (based on IEC Standard 60079-7) are allowed. Such motors and their controls are designed to ensure that surface temperatures cannot reach the atmosphere ignition point.

In either Division 2 or Zone 2, explosion-proof or dust-ignition-proof motor construction is not required. But motor surface temperature limits apply, and accessories or components that produce arcs or sparks are not permitted.

As a guide to applying motors in Division 2 areas, IEEE Standard 1349 was published in 2000. Experience in the petrochemical industry indicates that standard open or enclosed motors have no significant history of causing ignition of flammable atmospheres even with gas/air mixtures of the lowest commonly-encountered ignition temperatures.

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Featured Technical Article
November 2003

On this page is a summary of the Electrical Apparatus November 2003 featured technical article, by Richard L. Nailen, P.E. , "Applying Motors in Hazardous Areas -- What are the Rules?" Regeln über den Einsatz von Motoren in Gefahrenbereichen ... Utilisation des moteurs dans les endroits dangereus - Quelles sont les regles? ... La Utilización de los Motores en Sitios Pelgrosos. ¿Cuales son las Reglas?..

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