Storage rooms for flammable and combustible liquids should have ventilation systems that completely re-supply the air at least ____ times an hour.

The requirement for storage rooms containing flammable and combustible liquids to have ventilation systems that completely re-supply the air at least six times an hour is based on safety standards aimed at minimizing the risk of fire or explosion.

This frequency of ventilation helps to disperse vapors that may accumulate in the air, reducing the likelihood of reaching an explosive concentration. Proper ventilation is essential because flammable vapors can ignite if they come into contact with an ignition source. By ensuring that the air is exchanged multiple times within an hour, the ventilation system maintains a safe environment and enhances the overall safety of the storage area.

In comparison, lower ventilation rates would not effectively mitigate the risks posed by flammable vapors, making option six the minimum standard for safe operations. Adhering to such standards is crucial for the protection of workers, equipment, and the surrounding environment.