Pump stations are essential components of any water and wastewater collection and management system, but they could be the source of significant safety risks due to the potential accumulation of flammable and explosive gases.
The NFPA (70 & 820) Class and Division classification system categorizes hazardous locations based on the likelihood of having flammable gases or vapors inside the well. In this system, hazardous areas are divided into Class I, Class II, and Class III, where Class I focuses on flammable gases. In addition, in this standard, Class I is subdivided into Division 1, where hazardous conditions may exist under normal operations, and Division 2, where such conditions are not expected but may occur under abnormal circumstances.
Proper classification of hazardous areas, as guided by NFPA standards and addressed by the Canadian Standards Association (CSA Z462), is the first consideration in designing any underground lift stations to ensure the safety of the operator team and equipment. Wet wells usually handle fluids that can produce gases such H₂S and methane, and they are generally classified as Class I, Division 1 or 2, depending on several parameters, including gas concentration and exposure, ventilation, environmental factors, and site location. This makes it essential to consider explosion-proof equipment and adequate ventilation in the design of the wet wells, as highlighted in CSA C22.1, which is the primary standard for the installation and maintenance of electrical systems in Canada.
The International Electrotechnical Commission (IEC) standards (IEC 60079) define similar guidelines for installing and operating electrical equipment in hazardous areas where flammable gases or vapors may be present using a zoning system. Zone 0, Zone 1, and Zone 2 are defined based on the likelihood of exposure to explosive gases. Zone 0 refers to continuous gas presence, Zone 1 to frequent presence, and Zone 2 to occasional exposure. Like NFPA and CSA, the IEC standards emphasize using explosion-proof equipment and proper ventilation to prevent the buildup of explosive and dangerous gases, especially in confined spaces like wet wells and underground pump stations.
Although the risk of accumulated gases inside the rain and stormwater lift stations is less than in sewage and wastewater wet wells, it is still important to study and clarify their area classification due to the risk of unexpected contaminants, such as fuel, oil, and other chemicals, that may enter the station from surrounding areas such as roadways, an accident, or industrial plants.
It is a common practice for engineers and expert designers to maintain a Class I, Division 1 classification in most scenarios for wet well lift stations that handle sewage and wastewater. This approach offers maximum safety, mitigates the explosion risk, and safeguards operators and infrastructure. However, to have a tailored design meeting the project's unique requirements, we should always consider project specifications, site conditions, and local codes and regulations for safety and hazardous environments.