Fourteen Twenty at the Rack: Bonding, Outage, and a Missing Drop Tube
At 14:20 you are at a bulk terminal with a DOT-406 cargo tank, 9,000 gallons, four compartments, loading UN1203, Gasoline, 3, PG II. The weather is 96°F and the product is coming from an underground line. The terminal's bonding reel cable is frayed and the attendant says the trailer's own static strap is "good enough," so you can start top-loading. Your load sheet shows the No. 2 compartment is rated 2,500 gallons, and you plan to put 2,480 gallons in it because the customer wants a full drop. When you lift the dome cover you see the fill opening is 12 feet above the tank bottom and the drop tube is missing. The attendant wants to use the high-rate setting to finish before a shift change. Another truck is waiting behind you.
1. What do you do about the bonding problem, and why isn't the trailer's static strap enough?
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Do not start loading. The bond must run from the tank shell to the loading rack - bare metal to bare metal - and it must be connected before any dome cover is opened and removed last, after the fill is complete and the line is drained.
The trailer's own static strap does one thing: it bleeds static from the vehicle to earth. It does not equalize electrical potential between the rack piping and the tank shell, which is where the spark that ignites gasoline vapor comes from. A frayed reel cable is a broken bond, not an inconvenience.
What to do: shut the operation down, tell the terminal supervisor in plain terms that the bonding cable is unserviceable, and ask for a functioning reel or a different bay. Do not substitute a chain, a strap, or a jumper cable from another truck.
While the bonding issue is open, the missing drop tube is a second stop-work item. Top-loading into a 12-foot drop without a drop tube is splash loading - it generates static in the falling stream and produces far more vapor. It is prohibited for flammable liquids for exactly that reason.
2. Compute the outage question for the No. 2 compartment and decide what you can load. Show the reasoning.
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You cannot load 2,480 gallons. Cargo tank compartments for flammable liquids must retain outage - unfilled space - to allow for expansion; the minimum is 1 percent of the compartment's capacity.
- 1 percent of 2,500 gallons = 25 gallons of required outage.
- Maximum product = 2,500 − 25 = 2,475 gallons.
At 2,480 gallons you would leave only 20 gallons, or 0.8 percent - below the minimum. That matters more than usual today because the product is coming out of an underground line, so it is relatively cool, and it will warm toward the product's temperature in a tank sitting in 96°F ambient. Gasoline expands as it warms, and with almost no outage the liquid can push into the vapor recovery line, out the venting arrangement, or out of a dome if the cover is not fully seated.
Practical answer: load the compartment to 2,475 gallons or less, check the compartment's marked capacity against the load sheet rather than assuming, and recheck the outage on every compartment, not just the one you calculated first.
3. The attendant wants the high-rate setting and intends to leave you alone at the rack to do another task. How do you handle it?
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You refuse both parts of that plan.
- Attendance: the person loading a cargo tank of flammable liquid stays at the controls. You must be able to stop the flow instantly if a hose fails, a dome overflows, or a fitting lets go. If the attendant leaves, you stop the transfer - an unsupervised high-rate fill is how large spills start.
- High rate into a missing drop tube: high-rate top loading without a drop tube is the worst combination - maximum splash, maximum static generation, maximum vapor. Even with a proper drop tube, the rate has to stay within what the venting and the bonding can handle.
- The waiting truck is irrelevant. Shift change and a line behind you are schedule problems. A gasoline release at a rack is a fire and evacuation problem, and the tank you are filling is the ignition source.
Before opening the valve: confirm the bond, confirm the drop tube or switch to bottom loading, know where the emergency shutoff is, confirm the dome cover is positioned so the fill line enters properly, and have the spill kit and fire extinguisher where you can reach them.