Hazardous Area Terminology

Table of Contents

Certification Standards

Industrial products are certified to international standards for the installation and use of electrical equipment in hazardous areas.

Worldwide: The IEC defines the most-widely adopted hazardous area standards. These standards:

Classify hazards;
Areas (Zones) in which hazards may be present;
Protection used to prevent explosions in these areas (IEC 60079 series).

Many countries are replacing national standards and certification schemes, with IECEx conformance and require IECEx certification:

Europe: Products are certified to EN IEC standards under the ATEX scheme. We have full 3rd party approval under the relevant Directives and our Manufacturers Declaration of Conformity to European Standards (CE marking).
Brazil: Products have INMETRO certification to IEC standards.
Australia & Singapore: IECEx certification is already mandatory.

North America: the NFPA (National Fire Protection Association) is the primary agency for the protection of installations from fire and explosion.

NFPA70 is the National Electrical Code (NEC). It describes permissible electrical installations for residential, commercial and industrial uses.
Article 500, within the NEC. This categorizes hazardous locations & materials as Divisions and Classes.
Article 505 is a later addition. This classifies hazardous locations into Zones & Groups, following IEC guidelines.
NFPA496 is the Standard for Purged and Pressurized Enclosures for Electrical Equipment.

Hazardous Areas

Hazardous areas or locations are where the potential for fire or explosion exists because of gases, dust, or easily ignitable fibers or filings in the atmosphere. Hazardous areas are defined as

Zones under worldwide IEC standards;
Divisions under North American NEC standards.

North America: The level of safety equipment installed in each location, depends on:

Classes: the flammable materials in the atmosphere;
Divisions: the probability of the presence of flammable materials;
Groups: the flammable nature of the material.

In 1998 Canada introduced the “Zone” system for new hazardous area plants.

Worldwide: The classification of hazardous areas (locations) follows the IEC format:

Zones; define the probability of the presence of flammable materials;
Protection Types: denote the level of safety for the device;
Groups: classify the exact flammable nature of the material. NB. IEC groups are not the same as the USA’s NEC Groups.

T-Ratings

For both IEC and NEC, T-ratings indicate the apparatus’ maximum surface temperature under normal operation and specified fault conditions. The equipment’s T-rating must be lower than the hazardous material’s ignition temperature in that location.

The surface temperature is based on 40°C (104°F) ambient. The

IEC has T1 (450°C) through T6 (85°C);
NEC uses the same principles, but has more subdivisions – e.g. T3A, T3B, T3C.

Explosion Protection Techniques

The following describes explosion protection techniques to enable the use of electrical equipment in hazardous areas.

National or international standards and codes of practice govern each technique and define the equipment’s design and application.
National certifying (or approvals) authorities ensure design compliance.
National inspectorates (or insurance companies) vet and usually inspect each installation.

Flameproof [Ex d] IEC/European Harmonized Standard 60079-1
An enclosure contains the equipment. This enclosure will:

Withstand an internal explosion of flammable gas or vapour that may enter it;
Without suffering damage;
Without communicating the internal flammation to the external explosive atmosphere through any joints or structural openings.

The enclosure is designed for a particular gas grouping (I, IIA, IIB or IIC). Equipment using this protection method is:

Marked Ex d;
Suitable for Zone 1 and Zone 2 hazardous areas.

Usually Ex d equipment is large and robust, which limits its application to components.

Intrinsic Safety – Ex ia / Ex ib / Ex ic IEC/European Harmonized Standard 60079-11
This protection technique restricts the electrical energy within the equipment and interconnecting wiring. The energy is so restricted that it cannot cause ignition by sparking or heating.

Equipment in the hazardous area and the connected apparatus in the safe area must be certified as intrinsically safe. Also the whole system including interconnecting wiring must be assessed as “safe”. Certified independent bodies generally evaluate equipment. The user is responsible for system assessment.

The sub-types a/b/c define the equipment’s suitability for Zone 0, Zone 1 or Zone 2. The difference is performance under fault conditions:

Ex ia systems are safe even with 2 faults;
Ex ib systems are safe with 1 fault;
Ex ic systems are safe in normal operation (no fault).

Intrinsic safety is limited to low power circuits. It is mainly used for instrumentation and exposed measurement devices.

Pressurization [Ex p] IEC/European Harmonized Standard 60079-2
This protection method uses the pressure of a protective gas to prevent explosive gases or dust entering a space that might contain an ignition source. If that space contains equipment that emits gas, it prevents an explosive atmosphere by using a continuous flow of protective gas to dilute the atmosphere.