What is primarily found in sewer air that poses an explosive risk?

The primary concern regarding explosive risks in sewer air is the presence of methane. Methane is a byproduct of organic matter decomposition in the sewer system and is known for its flammability and potential for explosion in confined spaces. While hydrogen sulfide is indeed a toxic gas found in sewers, it is primarily hazardous due to its toxicity and potential to cause asphyxiation at high concentrations, rather than an explosive threat. Carbon monoxide, a colorless and odorless gas produced during incomplete combustion, poses serious health risks but is not typically associated with sewer systems. Hydrogen cyanide, a highly toxic chemical compound, is not a common contaminant in sewer air. Understanding the dangers of these gases is crucial for safety in plumbing and sewer maintenance, with methane being the main focus when assessing explosive risks.