Industries, such as petroleum, chemical, and pharmaceutical, use chemicals considered flammable and sometimes explosive; gasoline and natural gas are the obvious top two. Typically, where these are stored, handled, or transferred, the area needs to be classified, but most industries need to do some area classification.
The ISA12 standards committee has approved a newly revised ISA-60079-15 standard that specifies requirements for the construction, testing, and marking for Group II electrical apparatus with type of protection, “n” intended for use in Class I, Zone 2, hazardous (classified) locations as defined by the National Electrical Code, ANSI/NFPA 70.
Type protection “n” applies to electrical apparatus not capable of igniting a surrounding explosive gas atmosphere in a normal operation, and when a fault capable of causing ignition is not likely to occur.
The ISA-60079-15 standard is applicable to non-sparking electrical equipment, as well as electrical equipment with parts capable of producing arcs or sparks or having hot surfaces which, if not protected in one of the ways specified in this standard, could ignite a surrounding explosive gas atmosphere.
“The standard provides design requirements for equipment intended to be used in Zone 2 (or Division 2) hazardous locations,” said Rich Masek, chair of subcommittee ISA12.12 on apparatus for Division 2 hazardous locations, and a project manager for hazardous locations at CSA International, a provider of product testing and certification services for the U.S., Canada, and countries worldwide, for electrical, plumbing, gas, and mechanical products out of Wickliffe, Ohio.
The reason for the IEC designation instead of ISA is “there is a continuing effort to harmonize standards around the IEC standards,” Masek said. “It is confusing to those who buy standards when an IEC standard is adopted with national deviations, but then is given a different number such as ISA12.12.02. The committee is in agreement that when adopting IEC standards, the number on the standard should relate to the IEC standard number.”
Generally, users (those who buy equipment) would not need to use this standard, “but they would if they also need to design their own one-off equipment that will be located in a Zone 2 hazardous location,” Masek said. “Anyone involved with Zone 2 (or Division 2) hazardous locations would benefit from understanding this standard. Two new key aspects, external connectors and motors, now have requirements in the standard.”
The specific application is to Zone 2 (or Division 2) hazardous locations. There is a wide variety of process control equipment that can be made suitable for Zone 2. ISA-60079-15 is primarily intended to show requirements that do not rely on explosion-proof housings or on the intrinsic safety concept. So it generally is much less expensive.
In most cases, wherever flammable chemicals are used or stored, there is an area classified as Zone 2 (or Division 2). The big difference between divisions and zone is Zone 1. For all intents and purposes, Zone 2 and Division 2 are equivalent. The National Electrical Codes permit products certified as Division 2 to be used in Zone 2 and vice versa.
“Most electrical equipment is capable of producing an arc or spark. A typical arc or spark producing device is a switch,” Masek said. “This can be the on/off switch for the equipment or other switches, such as internal programming switches.”
Other parts that can produce an arc or spark are relays, motors with brushes, connectors, removable parts such as fuses and lamps, and sliding contacts such as potentiometers. “If the energy in the arc or spark is great enough, the flammable atmosphere will be ignited,” Masek said. “This standard provides the design requirements for eliminating arcing/sparking components or for making the arc or spark incapable of igniting the flammable atmosphere.”
Ellen Fussell Policastro writes and edits Standards.
Hazardous location types
The National Electrical Code (NEC) defines hazardous locations as those areas “where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings.”
Class I locations
Areas in which flammable gases or vapors may be present in the air in sufficient quantities to be explosive or ignitable:
Class II locations
Those areas made hazardous by the presence of combustible dust. Finely pulverized material, suspended in the atmosphere, can cause as powerful an explosion as one occurring at a petroleum refinery:
Class III locations
Areas where easily-ignitable fibers or flyings are present due to the types of materials being handled, stored, or processed. The fibers and flyings are not likely to be suspended in the air but can collect around machinery or on lighting fixtures and where heat, a spark, or hot metal can ignite them:
SOURCE: U.S. Department of Labor, Occupational, Safety, and Health Administration, http://www.osha.gov/doc/outreachtraining/htmlfiles/hazloc.html.