NEBOSH Practice Test

Which property of Hydrogen Sulphide (H2S) is most critical to safety in confined spaces?

1. Pungent odor

2. Heavier than air

3. Non-flammable

4. Highly soluble in water

The correct answer is: Heavier than air

In the context of safety in confined spaces, the critical property of Hydrogen Sulphide (H2S) is that it is heavier than air. This is important because when H2S is released, it tends to accumulate in low-lying areas or confined spaces that are poorly ventilated. The accumulation of this gas can create hazardous conditions, as higher concentrations near the ground can lead to suffocation or poisoning, especially because it may not be immediately detectable if the person is in a low-lying area. While the pungent odor is a significant property, indicating the presence of H2S, it can become less effective at high concentrations or if individuals become desensitized to the smell. Non-flammability is also a relevant characteristic, as it means H2S does not pose a fire hazard. However, the risk posed by inhaling hazardous concentrations in confined spaces far outweighs these other properties. The solubility of H2S in water is pertinent for understanding its behavior in certain environments but not as critical in the immediate assessment of risks within confined spaces where people are likely to be exposed. Hence, the factor of being heavier than air is the most critical consideration for safety regarding H2S in such scenarios.