May 20, 2020

Electrical classification of hazardous locations: wastewater treatment plants

  • Article
  • electrical classification
  • hazardous locations
  • wastewater treatment plants
  • NFPA-820
  • safety

According to the NFPA-820 2020 standard [1], most pumping stations, spaces and buildings that make up a wastewater treatment plant must be considered hazardous locations.

  1. In these classified areas [2] where an explosive atmosphere is possible or probable, electrical systems and apparatus must be:

    • properly designed and certified (e.g., explosion-proof motors).
    • securely connected (e.g., installation classified in accordance with the current electrical code with classified hardware and proper grounding practices).
    • meticulously inspected and maintained (e.g., visual, close-up and detailed inspections).

    Wastewater treatment plant managers and operators must also consider the following:

    • Under Section 18-004 of the Canadian Electrical Code[3] (CSA C22.1-18), they are legally obligated to identify areas where explosive atmospheres are likely to occur—the status quo is not an option.
    • There are two possible approaches to analyzing and diagnosing locations (either one of the following options or both):

      - Direct application of NFPA requirements[4].

      - Identifying optimization solutions that often significantly lower the number and scope of classified zones.

    Where to start

    Wastewater pumping and treatment emit flammable gases and vapours. These emissions come mainly from substances that the wastewater could be carrying (e.g., oils, solvents or gasoline from accidental spills) and from anaerobic digestion of organic matter (process).

    This is a known risk and reference documents like the NFPA-820 2020 standard establish a scale to guide design. The challenge is that wastewater treatment plants—whether they are recent or antiquated—may not have been designed to reflect the potential presence of combustible gases and vapours in explosive concentrations, and, as a result, often present a significant gap between the current level of safety and the targeted level. When using a conservative classification approach, applying measures involves major changes that are difficult to predict.

    Thus, we suggest the following complementary action plan:

    • Step 1 – Perform a general survey of the facilities (on site or remotely) and diagnose the current situation.
    • Step 2 – Establish the applicable classification based on two approaches (basic and optimization) for each area of the facility.
    • Step 3 – Assess the gap between the existing safety level and the compliance target for each analyzed area.
    • Step 4 – Find solutions to control risks, upgrade and ensure existing facility compliance, and establish an implementation strategy.

    Substantial savings

    Upgrading electrical installations that were not designed for hazardous locations can be tedious and costly for wastewater treatment plants. From simple sump pumps to major equipment like presses, filters or conveyors, replacing motors, starters, connectors and other connections can be a major challenge both in terms of equipment availability on the market[5] and the costs involved (e.g., installing a 50 HP standard motor costs $1,000, while the same motor for Zone 1 costs $4,000, or installing building electricity for a standard pump room costs $10,000, while the same installation for Zone 1 costs $30,000).

    When building areas are classified, electrical apparatus management, which includes inspection, servicing and maintenance, is very demanding and complex, and requires qualified resources who are adequately trained. Additionally, certain specific apparatus, such as gas detection systems, require frequent calibration (usually three times a year).

    When an optimization solution or control measures have been established, implementing them can prevent the total or partial classification of an area. For example, if ventilation is determined to be or may become enough to control the flammable gases and vapours[6] emitted by the process in a given area (e.g., pumps, tanks and basins, conveyors), it would be wiser to commit to improving ventilation rather than classifying the area. When optimization is possible, the return on investment is quick.

    Wastewater treatment plant operators have put BBA’s unique expertise to good use, demonstrating that optimizing control measures costs up to 10 times less than an equivalent prescribed upgrade. The benefits not only translate into safer and more compliant installations, but also into reduced inspection and maintenance requirements, and lower electrical apparatus maintenance and replacement costs. Result: increased operator safety and their work made easier.


    Managers at wastewater treatment plants must consider controlling explosion hazards and classifying hazardous locations, because flammable gas and vapours are present or may be present in explosive concentrations in certain equipment and areas.

    Reference standards, like the NFPA-820 2020 standard, provide recommendations for identifying and classifying hazardous locations in industrial facilities, but the resulting requirements are rather demanding and often create a significant gap between the reality of wastewater treatment plants and expected levels.

    A fundamental principle in classifying hazardous locations remains the need to reduce the scope and number of classified zones. A facility should therefore consist predominantly of unclassified locations or of Zone 2 and/or Zone 22 locations, i.e., locations where explosive atmospheres is unlikely to form. The physical scope (extent) of the zones with hazardous concentrations as well as their frequency and duration will decrease or even be eliminated. Containing emission sources and controlling flammable gases and vapours will be achieved through intelligent design of process systems and equipment and by implementing mitigation and control measures like ventilation, gas detection, partitioning or pressurization.

    An optimization approach will allow wastewater treatment plant managers to demonstrate that they are in full control of the risk and adequately meet applicable regulatory requirements, while achieving substantial savings on the costs of implementing, replacing and operating electrical equipment.

    The BBA team has ventilation experts who will help you control risks while saving you money.

    Interested in online training or looking for quick tips? Contact our experts.


    [1] Certain electrical equipment suitable for operation in classified areas may not be available on the market (non-existent or simply unsuitable for the intended use).

    [2] E.g., hydrogen sulphide (H2S), methane (CH4).

    [3] In Québec, the Canadian Electrical Code is applicable in accordance with the Safety Code, Chapter II – Electricity, and Québec’s Construction Code, Chapter V – Electricity, which consists of the Canadian Electrical Code, Part 1, 23rd edition and Québec amendments (CSA C22.10-18 standard).

    [4] For example, wet and dry wells for wastewater pumping stations as well as storage tanks and holding vaults, settling ponds and homogenization tanks are hazardous locations (zone 1 or class I, division 1).

    [5] National Fire Protection Association standard.

    [6] E.g., zone 0, zone 1 or zone 2; zone classification can also be in classes and divisions (e.g., class I, division 1; class I, division 2) based on the imperial system.

This content is for general information purposes only. All rights reserved ©BBA

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