Which locations may be hazardous due to an oxygen-deficient atmosphere?

An oxygen-deficient atmosphere can be a significant hazard in various confined spaces, and all the locations mentioned in the question can present this risk.

Sewers may experience an accumulation of gases such as methane or hydrogen sulfide, which can displace oxygen and create an unsafe environment. Manholes, similar to sewers, can collect harmful gases that may result in low oxygen levels. Septic tanks also pose a danger as the decomposition of organic matter produces gases that can reduce oxygen concentration.

Each of these environments has the potential to create an oxygen-deficient atmosphere due to the natural processes occurring within them, making the selection of all the options the most accurate choice. Understanding the risks associated with these specific locations is critical for safety when working in or around them.