Sampling of which gas in the air is required under normal working conditions for mines employing at least 500 workers on average?

• A. Carbon Monoxide (CO)
• B. Methane (CH4)
• C. Hydrogen sulfide (H2S)
• D. Oxygen (O2)

Answer: (A)

Monitoring air quality for carbon monoxide is required in mines with a large workforce to ensure ventilation is providing clean air and to detect buildup from engine exhaust or other combustion sources. Carbon monoxide is colorless and odorless, so it can accumulate without noticeable warning, making routine CO sampling essential in big operations. If CO levels rise, it signals ventilation problems or increased combustion by-products, prompting corrective actions to protect workers.

Other hazards like methane, hydrogen sulfide, and oxygen levels are also important in mining safety, but the requirement described here specifically targets carbon monoxide as a reliable indicator of air quality under normal operating conditions in large mines.