Sections 18 and 20 of the Canadian Electrical Code define hazardous locations and specify the types of electrical equipment and wiring methods acceptable in areas where flammable or explosive materials are handled, stored or produced. In such areas, the risk of a fire or explosion may exist due to the presence of flammable gases or vapours. The electrical code provides requirements for protection in hazardous locations, from electrical ignition sources, due to the effects of electrical arcing or heating.
Sections 18 and 20 have always seemed rather complicated to the average person. Now they may seem even more so, since we have just inherited two different methods for classifying Class I hazardous locations and methods of protection for each. As you begin to peruse the 1998 Canadian Electrical Code, Sections 18 and 20, you will notice some major changes. Class I locations are now defined as “explosive gas atmospheres,” which contain “a mixture with air, under atmospheric conditions, of flammable substances in the form of gas, vapour or mist–”. In other words, if a flammable or explosive gas, vapour or mist can occur, the area must be classified.
You will also discover that the two-division system has been replaced by three zones. At the beginning, I should point out that both systems result in a safe installation when equipment and wiring are correctly installed. In this article, let’s review the differences and similarities between the old system of classification and the new.
In the 1994 CEC version, Class I hazardous locations had two divisions:
Division 1 – where flammable gases or vapours exist:
- Continuously, intermittently or periodically
- Due to repair, maintenance or leakage
- Due to breakdown or faulty operation
Division 2 – where flammable gases or vapours:
- Are in closed systems or containers
- Where prevented by positive mechanical ventilation
- Next to a Division 1 location, with positive air pressure
In the 1998 CEC, the 1994 requirements have been moved to Appendix J, and the earlier requirements have been replaced by the new IEC system in Sections 18 and 20.
In the new 1998 CEC, Class I hazardous locations are divided into three zones in accordance with the European IEC classification system, which recognizes a higher hazard level than we are accustomed to in North America:
Zone 0 – where an explosive gas atmosphere exists continually or for long periods. It is estimated that such locations are found in only 1% of hazardous location installations. Under our Division system, Zone 0 would have fallen within Division 1, but with no special recognition of a higher hazard level.
Zone 1– where an explosive gas atmosphere:
- Is likely to occur in normal operation
- May exist due to repair, maintenance or leakage
- Is next to a Zone 1 location
Zone 2 – where an explosive gas atmosphere:
- Is unlikely, but may occur for a short time
- Flammable materials may be handled, stored, used or contained in a closed system
- Next to a Zone 1 location with positive air pressure
You may have noticed that the definitions for Zones 1 and 2 are almost identical to our old Divisions 1 and 2. The big change is Zone 0, which is intended to contain the most hazardous conditions.
In the 1998 CEC, the Scope paragraph of Section 18 prescribes application of the new zone classification system as follows:
- The Division system of classification may still be used for additions, modifications and renovations to existing facilities
- Appendix J requirements are to be followed when classifications are made in accordance with the Division system
- Class I, Zone 2 electrical equipment may also be installed in a Class I, Division 2 hazardous location
Eventually, you may find that the provincial and territorial electrical code authorities may still decide to amend the application of the new system of classification.
Where the old system required the use of explosion-proof electrical equipment, the new system permits a wider assortment of equipment types, all of which can satisfy code requirements when correctly applied.
Zone I Locations – may have equipment of the following types:
- Class I, Division 1
- Intrinsically safe – creates insufficient energy to ignite a fire or explosion
- Flameproof – similar to explosion-proof
- Increased safety – a method of ensuring connections don’t come loose, causing sparking or overheating
- Pressurized – using a protective gas
- Encapsulated – arcing contacts are enclosed within a com pound
Zone 2 locations – may have equipment of the following types:
- Class I, Division 1 or 2
- Intrinsically safe
- Equipment permitted in Zone 1
- Nonincendive – a form of intrinsic safety, but only incapable of causing an ignition under normal conditions
- No-arcing, sparking or heat- producing
In some cases, electrical equipment may use more than one of the above protection methods.
You may also have noted that wiring methods for Zones 1 and 2 are quite similar to Divisions 1 and 2, except that:
- Non-tapered threads are acceptable, but in some atmospheric groups, must have at least eight engaged threads
- Adaptors must be used where wiring systems and equipment have different threadforms
- Some equipment has factory- made seals and does not require field-installed seals
Only intrinsically safe electrical equipment marked ExI or Exia is permitted in Zone 0. Intrinsically safe circuits are usually instrument wiring to sensors in the Zone 0 hazardous locations. An example of a Zone 0 location is within the nozzle boot of a gasoline dispenser.
Intrinsically safe electrical equipment does not require a flame-proof enclosure, field-installed sealing or any other protection method. However, field-installed seals are required at:
- The point where conduit leaves a Zone 0 location
- The first termination after a cable enters the Zone 0 location.
All flammable gases and vapours are grouped according to their common explosive characteristics. Under the North American system, four levels are used – A, B, C and D. The IEC system uses three levels – IIA, IIB and IIC. Both designation systems are found in the 1998 CEC. In the IEC system, electrical equipment temperature codes are reduced from fourteen to six.
As in past articles, your local inspection authority should be consulted for a precise interpretation of any of the above in each province or territory as applicable.