46 CFR §98.25-75

1. (a)All enclosed spaces containing cargo tanks fitted with bottom outlet connections shall be provided with mechanical ventilation of sufficient capacity to assure a change of air every 3 minutes. Where cargo tanks are fitted with top outlet connections, the enclosed spaces containing such tanks shall be fitted with efficient natural or mechanical ventilation.
2. (b)Enclosed compartments in which machinery such as cargo pumps or vapor compressors are located shall be adequately ventilated.