Filling a Cargo Tank at Minus Eight
St. Cloud, 5:30 a.m., minus 8 °F. You are filling a DOT 406 cargo tank with unleaded gasoline, UN1203, PG II. The tank's marked capacity is 9,000 gallons and the water capacity on the data plate is 9,200 gallons. Your company's loading sheet for this run says 8,300 gallons. The rack operator has set the meter for 8,900 gallons and tells you the last three loads went out the same way: "Fill it, nobody's ever had a problem, and the customer pays by the gallon." Your delivery is a terminal near Kansas City where the afternoon high is forecast to be 62 °F, and the trailer will sit outside in the sun for at least two hours before it is unloaded. The shift supervisor at the rack has already gone home, and the operator says he cannot change the meter without written authorization.
1. Work the expansion numbers and explain why 8,900 gallons is not a safe fill for this trip.
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Gasoline expands roughly 0.07 to 0.10 percent per degree Fahrenheit, so about 0.7 to 1.0 percent per 10 °F of warming.
Loading at −8 °F and delivering into a 62 °F afternoon is a swing of about 70 °F. That is a volume increase of roughly 5 to 7 percent.
8,900 gallons × 1.05 ≈ 9,345 gallons; × 1.07 ≈ 9,523 gallons. The water capacity of the tank is 9,200 gallons and the marked capacity is 9,000. The product alone, before any outage, would exceed the physical volume of the tank somewhere in the 40s for ambient temperature.
That is what outage is for. The tank must be loaded so that thermal expansion during the trip still leaves headspace; your company's 8,300 gallons leaves about 700 gallons of room against a 9,000-gallon marked capacity, which absorbs the expansion with margin. The operator's "nobody's ever had a problem" is a statement about luck so far, not about this trip's temperature spread.
2. The meter is already set and the rack operator says he needs written authorization to change it. What do you do?
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Do not load 8,900 gallons, and do not sign for it.
Sequence: tell the operator plainly that the quantity is over the safe fill for the forecast and that you will not take it. Ask for the meter to be reset to the 8,300 on your loading sheet. If he will not act without authorization, call your company's on-call supervisor or dispatcher - a fuel haul is a 24-hour operation and someone has authority at 5:30 a.m. - and get the instruction confirmed to the rack, in writing or by recorded phone authorization to the terminal.
The pressure to resist is the "just take it and sort it out at the customer" logic. If you load it, the overfill is on your vehicle and your signature, and topping off later is not an option a full tank gives you. If no one will authorize the correct quantity, the truck leaves the rack empty or partly loaded at a documented amount. Write the refusal on the ticket.
3. Suppose you load to 8,900 anyway and are 150 miles down the road. What would an overfilled tank look like, and what do you do?
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The classic signs are a strong gasoline odor inside or around the truck, wet streaking on the tank shell running down from the vents or the manhole area, product visible at a vent, and fuel on the ground under the trailer when you stop. Expansion drives liquid, not vapor, out of the vents once the headspace is gone.
Those signs mean stop. Pull off at the first safe location away from buildings, traffic and ignition sources, shut down, and do not smoke or let anyone else do so. Do not open the manhole to "check" - that releases vapor and can spray product. Keep people back, notify your company immediately, and call for spill response and, if there is a release to the ground or a waterway, emergency responders.
Do not try to burn off the extra by driving to the destination. The remaining miles are the hottest part of the day, and the tank has no room left.