Bulk Packages and Cargo Tanks
A bulk package holds more than 119 gallons of liquid, more than 882 pounds of solid, or more than 1,001 pounds of gas, and is not a vessel or barge. Bulk packages include cargo tanks (MC-306/DOT-406 for flammable liquids, MC-331 for high-pressure gases like propane, MC-338 for cryogenic liquids). The candidate must know the surge hazard: in a partially filled tank, liquid can surge forward and push the vehicle. Baffles divide the tank to reduce surge. Outage (ullage) is the empty space left for expansion-never overfill a cargo tank. Vapor recovery and self-closing valves prevent spills. Key traps: confusing MC-306 (low-pressure, flammable liquid) with MC-331 (high-pressure gas); forgetting that cargo tanks require the N endorsement; and assuming a tank is safe to fill to the top (it isn't-leave outage). Also know that bottom-loading requires vapor recovery and grounding, and that a cargo tank must have its emergency shutoff and internal valves functioning. Rule of thumb: high-pressure gas = MC-331; flammable liquid = MC-306; cryogenic = MC-338. Worked example: A driver hauling propane (Class 2.1) is in an MC-331 cargo tank and needs both the H and N endorsements; the tank must not be filled beyond its outage limit.