Filling and Unloading a Gasoline Cargo Tank
You drive a DOT-406 cargo tank with a 9,000-gallon capacity, delivering gasoline to a Denver station. The terminal plans to load 8,650 gallons at 92°F. The cargo tank's filling limit is 95 percent of capacity. At the station, the unloading area slopes toward a storm drain, and the station's overfill protection is a simple whistle. You must connect the hose, bond and ground, and unload. The station manager asks you to leave the truck running to save the battery and to watch the gauge while he goes to lunch. There is a slight gasoline odor at the hose connection. You have 30 minutes of slack in your schedule, and the next delivery is in Boulder. The cargo tank has a current inspection sticker; the hose is 20 feet long and shows a worn gasket at the coupling.
1. Is the planned 8,650-gallon load legal? Show your calculation and explain the consequence.
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No. The filling limit is 95 percent of 9,000 gallons: 9,000 × 0.95 = 8,550 gallons. The planned 8,650 gallons is 100 gallons over the limit. Gasoline expands as it warms, and without enough outage the liquid can overflow or be forced out through the vent. At 92°F, the load is already warm, so the margin is important. I would tell the terminal to load no more than 8,550 gallons, and I would verify the actual volume on the gauge before signing. If the tank already has 8,650, I would not depart until 100 gallons are removed.
2. Describe the unloading setup and sequence at the station.
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Before unloading: park on the most level spot available, set the parking brake, chock the wheels, and shut off the engine. If the pump is engine-driven, follow the cargo tank's approved procedure, but do not leave the controls. Connect the ground from the truck to a known earth ground, then bond the truck to the storage tank. Connect the hose and vapor recovery line if required, and check the gasket and coupling. Block the storm drain with a drain cover or absorbent boom before opening any valve. Open valves slowly and watch the gauge and the overfill whistle. Stay at the controls for the entire transfer. Do not smoke, use a phone, or allow anyone to stand near the vent.
3. What do you do about the gasoline odor and the manager leaving for lunch?
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The odor is a warning. Stop the transfer, close the valves, and do not restart until the source is found. Check the hose coupling, gasket, and the tank connection with a combustible gas meter or soap solution; do not use a flame. If the coupling is worn, replace it or use another hose. The manager cannot leave the transfer unattended. Unloading must be attended at all times so the driver can shut down the pump if a hose fails or the tank overfills. I would tell him I will stop the transfer if he leaves. If he insists, I shut down, secure the truck, and call my supervisor. Also keep the storm drain blocked until the transfer is complete.