Volatile organics in municipal sewers: principal hazard If volatile compounds such as gasoline, oil fractions, alcohols, or ether enter municipal sewers, what is the foremost immediate risk to the system and workers?

Introduction / Context:
Sanitary sewers are confined spaces with limited ventilation. Introducing volatile organic compounds (VOCs) such as gasoline, ether, or alcohols can create flammable vapor mixtures that pose grave safety hazards to workers, the public, and infrastructure.

Given Data / Assumptions:

• Presence of low-boiling, volatile, flammable substances in sewer headspace.
• Potential ignition sources (sparks, electrical equipment, static discharge) exist.
• Confined space with pockets where vapors can accumulate above lower explosive limit (LEL).

Concept / Approach:
VOCs readily evaporate and can form combustible mixtures with air. In confined spaces, even small releases may accumulate and migrate. The most acute hazard is explosion and fire, which can occur before chronic effects (e.g., corrosion) become significant. This is why industrial pretreatment programs strictly prohibit discharge of flammables into sanitary systems.

Step-by-Step Solution:

Verification / Alternative check:
Incident case histories document manhole explosions and fires following gasoline or solvent discharges. Sewer entry protocols require LEL monitoring precisely for this reason.

Why Other Options Are Wrong:

Common Pitfalls:
Underestimating ignition sources; even routine maintenance equipment can ignite vapor-air mixtures if not intrinsically safe.

Final Answer:
explosion