Water Distribution D1/D2 Exam Practice 2025 – Complete Study Resource

Hydrogen sulfide is particularly known to affect the sense of smell because it has a characteristic rotten egg odor at low concentrations. However, at higher concentrations, it can quickly dull and then completely inhibit the sense of smell, making it difficult for individuals to detect its presence. This is dangerous because the loss of the ability to smell hydrogen sulfide can lead to exposure without awareness, increasing the risk of poisoning due to its toxic nature.

In contrast, while the other gases listed have various health impacts and can be dangerous, they do not typically impair the olfactory senses in the same manner as hydrogen sulfide. Carbon dioxide is not known to affect the sense of smell directly, chlorine is more associated with respiratory irritation, and methane is largely odorless in its natural state and not toxic, which means it wouldn't impair smell unless mixed with another gas that has a potent odor.