Construction Skills Certification Scheme (CSCS) Practice Test 2025 – All-in-One Guide to Master Your Certification Exam!

Hydrogen Sulphide (H2S) is a highly toxic gas that poses significant health risks, especially in environments where it is present, such as in sewers or industrial sites. The ability of H2S to cause unconsciousness within just a few breaths is due to its potent neurotoxic effects. When inhaled, even in small concentrations, it can rapidly affect the respiratory system and central nervous system, leading to dizziness, loss of coordination, and ultimately unconsciousness. This quick action makes it particularly dangerous, as individuals may not have enough time to evacuate or seek help after exposure.

The other options describe potential effects of hydrogen sulphide, but they do not highlight the immediate and severe impact that unconsciousness can have, which underscores the urgency of safety measures around this gas. While skin irritation and nausea can occur with certain levels of exposure, they often manifest with longer exposure times, whereas unconsciousness can result from acute inhalation. Furthermore, the statement that hydrogen sulphide has no harmful effects is inaccurate, as the gas is well-known for its toxicity and lethal potential in significant concentrations.