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I NTRODUCT I ON HAZARDOUS LOCATION DATA

Explosive Dust Atmospheres – Comparing Division and Zone Dust Groups

The main difference between the two systems for combustible or explosive dusts is that the Zone System has only two dust groups as opposed to the Class/Division system that has three. The Zone system also includes what the Class/Division system identifies as Class III simply as a third Dust Group (IIIA). This means installation Rules in the NEC and CE Code for explosive dust atmospheres become the same for Class II and Class III. Using the Class/Division system, the Rules for Class III installations and equipment are less stringent than those used for Class II.

ZONE DUST GROUPS DIVISION DUST GROUP Class II, Group E

TYPE OF DUST

ZONE DUST GROUP

Conductive dust

IIIC IIIB IIIA

Non-conductive dust Class II, Groups F, G

Combustible flyings Class III Locations

Equipment Standards for Hazardous Locations Determining which type of equipment is acceptable for a specific hazardous location is predicated by a combination of the installation codes, certification requirements, user requirements and the authority having jurisdictions. The following is a brief outline of the types of equipment for each location. Details on equipment construction are provided in the next section.

While Class/Division products are predominantly used in Canada and the US, other jurisdictions may permit their use. In some countries, North American companies are permitted to construct facilities using the Class/Division system and equipment. This needs to be confirmed with the local AHJ. Class I, Division 1 Equipment For Class I, Division 1 locations, most devices that produce ignition-capable arcs or temperatures must be installed in an explosionproof enclosure. The wiring system connected to these enclosures must be sealed (using explosionproof sealing fittings or cable glands) to prevent any internal ignition from escaping through the wiring connection(s). While the exceptions to this requirement are rare (examples such as oil immersed transformers, purged systems (to NFPA 496), submerged pumps with additional protective controls, etc.), and different product certification, installation rules and maintenance requirements often apply. Low energy systems often specify Intrinsically Safe (or Intrinsic Safety) technology. The “Intrinsically Safe” or “Intrinsic Safety” (IS) concept involves more than simply the purchasing and installing of a single product. IS systems are an engineered solution which evaluates everything from the power source to the end device (including all components and wiring). Intrinsic Safety installations are addressed in NEC Articles 504 and 505 and CE Code Appendix F. Class I, Division 2 Equipment There are more options for equipment design in Class I, Division 2 locations. Certain types of industrial or “non-hazardous” equipment, such as terminals and

Class/Division Equipment Electrical equipment must be designed and

manufactured so that it does not become a source of ignition when installed in a hazardous location. The NEC and CE Code are very specific on which types of equipment are permitted to be installed in the various hazardous locations and equipment must be certified or approved by a Nationally Recognized third-party Certification Body. The certification of equipment also addresses any NEC and CE Code installation requirements that may apply. The US Occupational Health and Safety Administration (OSHA) registers Nationally Accredited Testing Laboratories (NRTL) that are approved to test and certify equipment to ANSI and other hazardous location Standards. The Standards Council of Canada (SCC) registers Certification Bodies (CB) to test and certify equipment to Canadian hazardous location Standards. In many cases, NRTLs and CBs are registered with both OSHA and SCC to simplify North American approvals. In both cases, acceptance of an NRTL or CB is determined by the Authority Having Jurisdiction (AHJ) responsible for the installation (AHJs do not always accept every NRTL or CB).

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