Texas Wastewater Class B Practice Exam

Which of the following gases is potentially dangerous and may be found in lift stations and manholes?

1. Chlorine

2. Nitrogen dioxide

3. Hydrogen sulfide

4. Carbon monoxide

The correct answer is: Hydrogen sulfide

Hydrogen sulfide is indeed a potentially dangerous gas that can be found in lift stations and manholes. It is produced by the decomposition of organic matter in anaerobic conditions, which are common in wastewater systems. This gas is particularly hazardous because it is colorless, has a characteristic rotten egg smell at low concentrations, but can quickly become odorless at higher concentrations. Exposure to hydrogen sulfide can lead to serious health risks, including respiratory distress, unconsciousness, and even death, particularly in confined spaces such as lift stations and manholes where ventilation may be poor. While chlorine is used as a disinfectant in wastewater treatment and nitrogen dioxide can be a byproduct of combustion processes, they are typically not found within wastewater systems in the concentrations that pose the same risk as hydrogen sulfide. Carbon monoxide, although toxic, is more commonly associated with incomplete combustion and might not be as prevalent in wastewater facilities as hydrogen sulfide. Therefore, hydrogen sulfide is the correct answer as it is a significant safety concern in lift stations and manholes.