5,400 Gallons of Gasoline at 95 Degrees
You are at a terminal rack loading a four-compartment DOT-406 tanker with regular gasoline, UN 1203, PG II. Compartment shell capacities are 1,800 / 1,400 / 1,400 / 1,400 gallons. The bill of lading calls for 5,400 gallons split 1,500 / 1,300 / 1,300 / 1,300. The rack attendant says the previous driver filled compartment 1 to its 1,800-gallon shell capacity 'to save a stop,' and mentions the vapor recovery line has been tripping. Ambient temperature is 95°F and the product in the line is about 60°F. Placards are in place on both sides and the rear; the front placard holder is empty.
1. Is filling compartment 1 to 1,800 gallons safe at 95°F? Show the expansion arithmetic.
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Gasoline expands roughly 0.09 to 0.1 percent per degree Fahrenheit. From a 60°F reference to 95°F is a 35-degree rise, about 3.3 percent. Take 1,800 gallons times 1.033: roughly 1,860 gallons. That is 60 gallons more than the compartment can hold.
A compartment filled to the shell has no outage, which means the liquid has nowhere to go as it warms on the road. It pushes out the vent, past the gasket, or through a dome cover, and a small gasoline spill on a hot day next to a hot engine is a fire, not an inconvenience. The correct fill is the planned 1,500 gallons with a deliberate outage, and a larger outage in hot weather. The tripping vapor line is a second warning: if the vent path is restricted, the pressure has to escape somewhere, and the dome cover becomes the relief valve.
2. What do you do about the empty front placard holder and the shipping paper?
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5,400 gallons at roughly 6.3 lb per gallon is about 34,000 lb of a Table 2 hazardous material. The placarding threshold is 1,001 lb, so you are thousands of pounds past it and the vehicle needs placards on all four sides, front included, plus the hazard class. Get a front placard before the truck leaves the rack; a missing front placard is one of the easiest things for an inspector to see and one of the easiest violations to avoid.
Then check the paper against the truck, not the other way around: the UN number, proper shipping name, hazard class, packing group, total quantity, and the compartment split. If the split on the paper does not match what is actually in the barrel, the paper is wrong and the load is not ready. Correct the paperwork at the rack rather than at the scale house.
3. How should the 5,400 gallons actually be distributed, and why isn't simply topping off the big compartment the right answer?
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Total product is about 34,000 lb, and with trailer tare around 14,000 lb you are near 48,000 lb gross, well under 80,000. So gross weight is fine and distribution is the whole problem.
The planned split of 1,500 / 1,300 / 1,300 / 1,300 fills three compartments and leaves the front one two-thirds full. That is a reasonable pattern: keep the weight low and centered, hold enough on the front group to keep the steer axle loaded without exceeding its 12,000-lb limit, and limit the number of partially filled compartments. A free surface in every compartment is worse than a free surface in one. Topping off compartment 1 and running the rest lighter moves weight rearward, unloads the steer axle, and leaves less outage in the hottest compartment. Confirm the result on a scale.