Methods of Protection Area Classificiation Systems Summary of commonly used protection methods for different div. & zones Apparatus Grouping Temperature code & Temperature class Testing Facilities Standards and Protection

Technical Information and Requirements

There are several ways to protect electrical equipment so that hot components will not be an ignition source causing an explosion.

• Explosion-proof or flameproof protection requires an enclosure that:
  • can withstand an internal explosion without rupture, and
  • prevents flame or an explosion inside the enclosure from causing an explosion in the surrounding atmosphere outside the enclosure.

This is the usual protection method used in North America for heavy industrial equipment.

• Intrinsic safety involves limiting the electrical energy at potential sources of ignition in electrical circuits (hot components and spark sources) to such low levels that even under abnormal (fault) conditions-there is no possibility of the electrical energy igniting an explosive atmosphere. This method of protection may be used for a wide range of low power equipment, including pagers, process control tank level transmitters, and portable gas detectors.
• Non-incendive equipment also limit energy at potential sources of ignition in electrical circuits (hot components and spark sources). But unlike the intrinsic safety method described above, non-incendive equipment is designed to provide protection only under normal operating conditions, which may include the opening, shorting or grounding of field wiring. This method of protection may be used for a wide range of equipment, including pagers, process control tank level transmitters, and portable gas detectors.
• Increased safety protection establishes safeguards against the possibility of gas or vapor mixtures being ignited by high temperatures or arcing or sparking under worst-case operating conditions. Increased safety is typically applied to luminaires, motors, and junction boxes.
• Pressurization involves using a protective gas to purge and maintain an internal pressure in the equipment. This prevents an external potentially explosive atmosphere or flammable gas or vapor from leaking into the equipment and contacting otherwise unprotected components. Pressurization is used in equipment such as motors, control panels, and gas chromatographs.
• Encapsulation involves molding the parts that could cause an explosion in a compound to exclude the external atmosphere. It is usually applied to components, such as valve solenoids.
• Dust-tight construction of electrical equipment prevents the entry of combustible or electrically conductive dust in Class II hazardous locations. A bin level indicator would be a typical application.

For exact definitions, see the Canadian Electrical Code, Parts I and II, available from CSA. To order the Code, visit our On-line store.

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Area classification systems

North America

In North America, hazardous locations have traditionally been defined by the following combination of Class and Division:

Class I - A location where a quantity of flammable gas or vapor, sufficient to produce an explosive or ignitable mixture, may be present in the air.

Class II - A location made hazardous by the presence of combustible or electrically conductive dust, including Groups E (metal dust), F (coal dust) and G (grain dust).

Class III - A location made hazardous by the presence of easily ignitable fibres or flyings in the air, but not likely in sufficient quantities to produce ignitable mixtures.

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Division 1 - A location where a classified hazard is likely to exist.

Division 2 - A location where a classified hazard does not normally exist but is possible under abnormal conditions.

For example: In Class I, Division 1, flammable gases or vapours could exist in quantities sufficient to produce explosive or ignitable mixtures under normal operating conditions; in Class I, Division 2, flammable volatile liquids are normally confined within closed containers from which they can only escape as a result of accidental rupture.

International

Internationally (and more recently in North America, for Class I hazardous locations), areas where explosive gas atmospheres are likely to be present are divided into three IEC-defined Zones:

Zone 0 - An area in which an explosive gas atmosphere is continuously present or present for long periods.

Zone 1 - An area in which an explosive gas atmosphere is likely to occur in normal operation.

Zone 2 - An area in which an explosive gas atmosphere does not normally exist.

For exact definitions, see the Canadian Electrical Code, available from CSA. To order the Code, visit our On-line store.

Area classification - Division versus Zone

Comparing Divisions versus Zones

Division 1 corresponds closely to Zones 0 and 1. Division 2 corresponds closely to Zone 2. The most important difference between the Division and Zone systems is the difference in marking conventions. Division markings identify the locations where the product could be used. The markings for the Zone method show the type of protection, according to IEC 60079 Series standards-for example, "ia" (intrinsic safety) or "d" (flameproof).

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Summary of commonly used protection methods for different Divisions and Zones

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Apparatus Grouping

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Temperature Code & Temperature Class

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Testing Facilities

CSA International's hazardous locations laboratories provides the expertise, test facilities, and services needed to evaluate your products in accordance with applicable CSA, UL, FM, CENELEC and IEC standards.

The explosion test chamber is designed to contain test gas mixtures for evaluating flame propagation and for determining maximum explosion pressure.

The overpressure test system includes hydrostatic test apparatus capable of delivering 18 gallons (68 litres) per minute at a maximum pressure of 3,000 psig (20,684 MPa). In addition, a hydraulic system is available for testing leak-free equipment to a maximum pressure of 40,000 psig (275,790 MPa). These systems are used to test an enclosure's ability to withstand pressure. This pressure withstand test is based on a multiplier of the maximum explosion pressure obtained in the explosion pressure test.

The IEC spark ignition test apparatus is used to evaluate the inductive, capacitive, and resistive energy levels of circuits for intrinsic safety or non-incendive circuit ratings with representative ignition-sensitive test gas mixtures. Our refinements help to ensure optimal sensitivity and repeatability. Specially modified units are available for low-voltage, high-current applications.

The component incendivity test system uses a see-through test chamber for evaluating non-incendive devices, such as switches, relays, and connectors, with electrical overloads applied in a simulated explosive atmosphere. The test chamber can be used for spark ignition testing of electrostatic paint spray guns.

The thermal ignition test chamber exposes small components, such as transistors and resistors that reach temperatures of more than 160oC, to a uniform ether/air test mixture. If the test mixture does not ignite with the component at its maximum temperature, the component qualifies for the corresponding temperature "T" Code or Class marked on the equipment. The apparatus is also used to check the ignition capability of lamp filaments.

Combustible gas detectors are used to enhance the safety of operations in hazardous locations. Our performance test facility is equipped to handle portable, mobile, and stationary instruments, including system applications. Specialized test equipment consists of:

• bounce apparatus
• two-stage regulated gas mixing supply
• primary standard reference gas mixtures
• gas environment exposure chambers
• small-volume sensor chamber for extreme temperatures
• gas flooding apparatus
• drop-out pulse generator for power interrupt simulation.

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Standards and Protection

Contact Us Hazloc@CSA-International.org

Inquire about our hazloc certification services. With our response we will also send a free hazloc poster.

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