How to properly handle safety issues with electrical equipment in hazardous areas.
BY SIMON FRIDLYAND
An area in any industrial facility classified as hazardous is one in which the atmosphere contains, or may contain, flammable or explosive gases, dusts or fibres. In this type of area, a fire or explosion could occur when three basic conditions are fulfilled:
1. Flammable gas, vapour, dust or fibres must be present.
2. The combustible material must be mixed with air in the proportion required to produce a flammable mixture.
3. A source of ignition must act to ignite the mixture. This can be any source that could release sufficient energy to cause ignition. A spark or even a hot surface may release the incendiary energy.
Generally, a potential source of ignition from an electrical system is any spark or hot component that release energy sufficient to ignite the combustible mixture surrounding it.
The ignition source may occur in any of four mechanisms: a) discharge of capacitive circuits, b) interrupting (opening) of inductive circuits, c) opening or closing of resistive circuits with slow intermittent interruption increasing the ignition capability (hazard), and d) high temperature sources.
Ignition mechanisms may occur in relay contacts, switch contacts, fuses, short circuits (from damage or component failure), and arc-over between components or conductors. However, the components or circuits that present a potential ignition source may be designed in a variety of ways in order to prevent the ignition of a hazardous atmosphere.
Three basic approaches are used individually or in combination to prevent the ignition of hazardous atmospheres:
1. Intrinsically Safe/Non-incentives Equipment: Eliminates the ignition source by designing equipment that cannot cause ignition when in contact with flammable or explosive atmospheres.
2. Gas Purge/Hermetic Sealing: Controls the atmosphere surrounding the potential ignition source so those components are enveloped within a non-hazardous atmosphere.
3. Flame-proof/Explosion-proof Housing: Contains the explosion within the housing, preventing the ignition of the surrounding atmosphere.
Regulations require than an area classified as hazardous be established by an engineer. In Ontario, for example, drawings of a classified area shall be stamped by a professional engineer, operating under a Certificate of Authorization issued by the Association of Professional Engineers of Ontario (APEO).
The electrical inspector from an electrical inspection agency (Ontario’s Electrical Safety Authority — ESA — for example) reviews the installation drawings for wiring methods in each classified area of a plant or other industrial facility and any safety devices such as dust collectors, ventilating equipment, etc., that might have an impact on the installation methods with reference to the stamped drawings. The electrical inspector ensures that the wiring and equipment installed conforms with the requirements of each area.
Any time electrical equipment is destined to go into a classified area, regulations state it shall be reviewed by a professional engineer before it is built. There are two reasons for this.
First, Ontario Electrical Safety Code Bulletin 18-1-15, as well as Ontario Regulation 851 Section 7, stipulate that a PSR (Pre-start Health and Safety Review) is required when dealing with flammable liquids, potentially explosive processes or dust collectors.
A Pre-Start Health and Safety Review is required if — in a factory other than a logging operation — a provision from the regulation and the circumstances described exist:
(a) When a new apparatus, structure or protective element is to be constructed, added or installed or a new process is to be used, or
(b) When an existing apparatus, structure, protective element or process is to be modified and one of the following steps must be taken to obtain compliance with the applicable provision: (i) New or modified engineering controls are used. (ii) Other than new or modified measures are used. (iii) A combination of new, existing or modified engineering controls and other new or modified measures is used.
Since a PSR is required, it makes sense to work with the equipment manufacturer at the design stage. It is possible for purchasers to pass on the responsibility for PSRs to their suppliers before the shipment is accepted by using the services of an engineering consulting firm. The firm can work with suppliers and end-users during the manufacture of the equipment, advise the supplier about the local compliance requirements, and co-ordinate any potential issues with the end-users. This approach ensures that when equipment arrives at its final destination, it is ready to be immediately operational, as the PSR will come with the equipment.
The second reason relates to the fact that electrical field evaluation agencies do not do field evaluations of electrical equipment in hazardous areas. Therefore, the design of the equipment has to be reviewed by a professional engineer before it is built, and the client advised as to whether to use approved and certified electrical components acceptable to the ‘Authority Having Jurisdiction in Canada’, or whether it must conduct additional tests by testing laboratories accredited by the Standard Council of Canada. Generally, both of these tasks are combined to reduce and minimize the expenses associated with the compliance process.
Simon Fridlyand, P.Eng., SAFE Engineering Inc., specializes in industrial health and safety issues and PSR compliance. For more information, visit www.safeengineering.ca.