Hazardous Area Classification (HAC) in Water and Wastewater Treatment Plant

BBA was mandated to assess hazardous locations and define a hazardous area classification at the wastewater treatment plant for the City of Montréal. This installation is the second largest in the world and defining hazardous locations, or “electrical classification,” based on general and conservative principles like those prescribed by the NFPA-820 standard, was not at all suited to the station’s reality.

Client: City of Montréal, Wastewater Treatment Plant
Location: Montréal, Québec


So, BBA decided to perform a tailor-made analysis based on defining specific risks associated with the process reality, resulting in optimized classification. In addition to substantial cost savings for the City of Montréal, using this approach made it possible to accurately define the real risks incurred at the station, thereby targeting corrective actions.

Our experts initially identified all the “risk scenarios”, i.e., conditions necessary to release flammable gases or vapours, potentially producing an explosive atmosphere. Thanks to a study approach suited to the site’s reality, operating conditions and the nature of existing effluents, and after analyzing the history of activities spanning over 40 years, we proposed mitigation solutions. The solutions that were implemented included specific ventilation (dust collection), general ventilation (dilution), gas detection and strengthening staff management, maintenance and awareness.

We then prepared a comprehensive study report for the main wastewater treatment plant (Jean-R. Marcotte). This report included:

  • Results of the station’s historical analysis (accounts, event history)
  • A description of the “risk scenarios” associated with the water treatment processes
  • Strategies and solutions to optimize classification of hazardous locations
  • A set of classification drawings (including a master plan of the treatment plant) to identify hazardous locations and reveal the selected conditions for analysis

BBA also prepared a practical guide for the hundred or so pumping substations in the municipal network, some that were nearly fifty years old. This document included a flowchart so the owner could establish classifications for existing substations. Finally, our experts also defined the design criteria for several pumping plants that were being refurbished, resulting in significant savings for the City of Montréal.

Our experts met the challenge of providing the client with tools that are easy to understand and use to optimize hazardous location classification.


“Thanks to BBA’s optimization approach, we were able to significantly reduce classification impacts and improve risk control at the source.”

Jacques-Olivier Gauvin, P.Eng., Project Manager BBA


  • Largest wastewater treatment plant in Canada
  • Average flow rate of 25 m3/s
  • Over 100 pumping substations operating 24/7 on the network