Hazardous locations: the game rules - Part 2

Distribution method (classification) for hazardous locations

In Canada, the Standards Council of Canada, through the Canadian Electrical Code of the Canadian Standards Association, has consensually decided to adopt the so-called international classification method known as the “Zone system of classification”. Historically, Canada’s approach was modelled on the method prescribed in the U.S. National Electrical Code (NFPA-70) and therefore the classification of hazardous locations was based on the Class and Division system of classification (e.g., Class I, Division 2).

According to the current edition of the Canadian Electrical Code (CEC), hazardous locations are defined as “[…] premises, buildings, or parts thereof in which:

• an explosive gas atmosphere is present, or may be present, in the air in quantities that require special precautions for the construction, installation, and use of electrical equipment.
• dusts are present, or may be present, in the form of clouds or layers in quantities to require special precautions for the construction, installation, and operation of electrical equipment.”

It’s important to note that the 2015 edition of the CEC includes a specific definition for locations where “combustible fibres or flyings are manufactured, handled or stored”. In the 2018 version, this type of location is no longer in effect, as the particles or fibres are included in the definition of combustible dust if they are “500 μm or smaller (material passing a No 35 standard sieve as defined in ASTM E11) and present a fire or explosion hazard when dispersed and ignited in air.”

Hazardous locations must be divided as follows [1]:

• Zone 0 – A location in which explosive gas atmospheres are present continuously or are present for long periods.
• Zone 1 – Location in which:
  
  - explosive gas atmospheres are likely to occur in normal operation.
  
  - explosive gas atmospheres could be communicated from an adjacent Zone 0 location.
  
• Zone 2 – Location in which:
  
  - explosive gas atmospheres are not likely to occur in normal operation, except for a short period.
  
  - explosive gaseous atmospheres could be communicated from an adjacent Zone 1 location, unless the possibility of communication of such gaseous atmospheres is prevented by adequate positive-pressure ventilation from a source of clean air and effective safeguards against ventilation failure are provided.
  
• Zone 20 – A location in which an explosive dust atmosphere, in the form of a cloud of dust in the air, is present continuously, for long periods or frequently.
• Zone 21 – A location in which an explosive dust atmosphere, in the form of a cloud of dust in the air, is likely to occur in normal operation occasionally.
• Zone 22 – A location in which an explosive dust atmosphere, in the form of a cloud of dust in the air, is not likely to occur in normal operation but, if it does occur, will persist for a short period only.

Since 1998 for explosive gas atmospheres and since 2015 for explosive dust atmospheres, the classification approach recommended in Canada, including Québec, is that defined in the international standards of the IEC 60079 series[2]. Any new construction must comply with the Zone system of classification. The former Class and Division system of classification is therefore being phased out. However, according to section 18-000 (CEC 2015 and CEC 2018), where the “old” system of classification is used, it is permitted to continue to follow the corresponding method for additions, modifications, renovations to, or operation and maintenance of existing facilities. This means that for many years to come, as long as there are “old” industrial buildings in Canada, designers, manufacturers and users will have to be able to exercise their “bilingualism” in area classification!

Why and how to classify?

When flammable gases, flammable and combustible liquids, and/or combustible dust are deemed to be present, production areas and plant sectors, as well as process equipment and systems, must be carefully analyzed; where it’s established that the presence of an explosive atmosphere is possible or even probable, the areas and enclosures under examination are classified as hazardous locations. In accordance with section 18‑050 of the CEC[1], “electrical equipment for use in hazardous locations shall be suitable for the specific explosive atmosphere that will be present.” In other words, the higher the probability of such an atmosphere being present, the greater the equipment protection level (thus, the lower the possibility of an ignition source being present). In the end, statistically, the probability of explosion is equivalent, regardless of the location/equipment combinations:

• Zone 0 hazardous location requires at best no electrical device or at least only equipment suitable for such location certified as EPL[2] Ga, Intrinsic safety (ia)[3], Encapsulation (ma), Flameproof (da), Inherently safe optical radiation (op is) or Optical system with interlock (op sh)
• Zone 1 hazardous location requires equipment suitable for such location certified as EPL Gb, Intrinsic safety (ib), Encapsulation (m, mb), Flameproof (d, db), Increased safety (e, eb), Pressurized enclosure (p, px, pxb, py, pyb), Powder filling (q, qb), Oil immersion (o, ob), etc.; equipment suitable for Zone 0 and for Class I, division 1 are also permitted
• Zone 2 hazardous location requires equipment for such a location certified as EPL Gc, Intrinsic safety (ic), Encapsulation (mc), Flameproof (dc), Pressurized enclosure (pz, pzc), Type of protection (nA, nC, nL, nR), Increased safety (ec), Oil immersion (oc), etc.; equipment suitable for Zone 1 and for Class II, division 2 are also permitted
• No specific requirements are related to unclassified locations; however, ordinary electrical equipment might not be adequate[4].

Subject matter experts have the competence and responsibility to establish the classification of hazardous locations and their boundaries (extents); knowledge of the process and related elements, such as ventilation and human behaviour, is required to perform quality work. Specialists and experts who classify the locations engage their professional liability for risk management. If they believe they have limited knowledge in this area, they should make sure to have the right people around them to carry out this exercise, which can be complex.

Classify, yes, why not declassify?

Classifying is assigned to a process or source of risk where there is no other way to manage the risk. BBA goes further and has stood out for its ability to revalidate the foundations of risk. As stated in the IEC 60079-10-1 standard, Zone 0 and Zone 1 areas “should be minimized in number and extent by design or suitable operating procedures”; moreover, “plants and installations should be mainly Zone 2 or non-hazardous”. In many cases where gas compositions can be changed or even evacuated, risks can be controlled and reduced at the source, without having to classify areas as hazardous. A study can therefore prevent significant installation costs. Would you like to optimize your classification and declassification practices? Give BBA a call!

References

[1] Section 18-002 (CEC 2015 and CEC 2018).

[2] International Electrotechnical Commission (IEC).

[3] Editions 2015 and 2018.

[4] Intrinsically safe: Electrical equipment designed and installed so that there are no sparks or heat build-up during normal or abnormal operating conditions that can cause ignition of any flammable gas, vapour or dust used.