Which gas has a legal limit expressed as 1.25%?

Study for the NSW Deputy Coal Mine Exam. Prepare with detailed multiple choice questions, each with hints and explanations. Master test content on your way to certification!

Multiple Choice

Which gas has a legal limit expressed as 1.25%?

Explanation:
Carbon dioxide is the gas whose regulatory limit is given as a percentage of the air, specifically 1.25% by volume. This reflects its role as an asphyxiant: as CO2 builds up in the mine air, the amount of oxygen available for breathing decreases, so a limit expressed as a percent signals when ventilation or evacuation actions are required. The other gases are typically regulated using different units—toxics like NO2 and SO2 are tracked in parts per million, and methane is governed by its relation to the lower explosive limit—so their limits aren’t stated as a fixed percent in air.

Carbon dioxide is the gas whose regulatory limit is given as a percentage of the air, specifically 1.25% by volume. This reflects its role as an asphyxiant: as CO2 builds up in the mine air, the amount of oxygen available for breathing decreases, so a limit expressed as a percent signals when ventilation or evacuation actions are required. The other gases are typically regulated using different units—toxics like NO2 and SO2 are tracked in parts per million, and methane is governed by its relation to the lower explosive limit—so their limits aren’t stated as a fixed percent in air.

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