Which of the following is a potential source of flammable or explosive gases in sewers?

Accidental discharges are a potential source of flammable or explosive gases in sewers because these incidents can introduce volatile substances, such as hydrocarbons or organic solvents, into the sewer system. When these substances mix with other materials in the sewer, they can create a highly combustible atmosphere. Furthermore, certain chemicals may produce flammable gases as they break down. Inadequate ventilation in sewer systems can lead to the accumulation of these gases, increasing the risk of explosion or fire.

While rain runoff can introduce contaminants into sewer systems, it typically does not lead to the accumulation of explosive gases. Low temperatures generally do not contribute to the generation of flammable gases, and wind conditions do not directly influence the gases present in sealed sewer systems. Therefore, the concern for flammable or explosive gases is most closely associated with accidental discharges.