Nickel - cadmium battery shops will be mechanically ventilated to provide how many air changes per hour in order to ensure the removal of any hydrogen gas?

• A. 3-4
• B. 1-2
• C. 5-6
• D. 7-8

Answer: (A)

Hydrogen gas is produced during charging of nickel–cadmium batteries, and it can form an explosive mixture with air if it accumulates. To prevent dangerous buildup, the shop’s air must be refreshed continually so the gas is diluted and removed. Air changes per hour measure how many times the entire room air is replaced in an hour, and for battery charging areas this dilution is achieved with a mechanical ventilation rate of three to four air changes per hour. This range provides enough dilution to keep hydrogen concentration well below the 4% lower explosive limit without wasting excessive energy from over-ventilation. Going with too few changes risks accumulation, while much higher rates aren’t necessary for typical Ni–Cd charging operations.