Which ventilation instrument is essential for recovery work in mines?

The anemometer is essential for recovery work in mines because it measures the velocity of airflow within the mine's ventilation system. Proper ventilation is crucial in mining environments, as it helps to ensure that fresh air is supplied to work areas while also eliminating harmful gases or dust. The anemometer enables mine foremen and safety personnel to constantly monitor air movement, assess ventilation effectiveness, and maintain safe working conditions for miners. Accurate airflow measurements are vital when planning recovery operations, especially in situations where there might be a risk of gas buildup or reduced oxygen levels.

In contrast, while the barometer, manometer, and thermometer provide useful measurements related to atmospheric pressure, air pressure, and temperature respectively, they do not directly gauge air movement within the mine, which is critical for maintaining a safe environment during recovery work.