Code of Federal Regulations Title 46. Shipping § 46.151.25–1 Cargo tank

(a) Inerted. All vapor spaces within the cargo tank are filled and maintained with a gas or vapor which will not support combustion and which will not react with the cargo.

(b) Padded. All vapor spaces within the cargo tanks are filled and maintained with a liquid, gas (other than air), or vapor which will not react with the cargo.

(c) Ventilated (forced). Vapor space above the liquid surface in the tank is continuously swept with air by means of blowers or other mechanical devices requiring power.

(d) Ventilated (natural). Vapor space above the liquid surface in the tank is continuously swept with atmospheric air without the use of blowers or other mechanical devices requiring power (e.g., “chimney-effect” ventilation).

(e) Dry. All vapor space within the cargo tank is filled and maintained with a gas or vapor containing no more than 100 ppm water.