Which substance is prohibited from discharge due to creating a fire hazard?

The correct answer identifies flammable materials as the substance prohibited from discharge due to their potential to create fire hazards. Flammable materials can ignite easily and burn with great intensity, posing a significant risk both at treatment facilities and within the broader environment. Allowing such materials to enter wastewater systems could lead to hazardous situations, including fires or explosions, which could harm personnel, damage infrastructure, and pose broader safety issues.

Heavy metals and lead, while harmful to aquatic life and human health, do not typically present an immediate fire risk in the same way that flammable materials do. Strong acids can cause corrosion and damage to systems but are not classified primarily as fire hazards. Thus, the focus on flammable materials highlights the specific dangers related to fire safety in wastewater management. Understanding this distinction is crucial for ensuring safety and regulatory compliance in wastewater treatment processes.