Unloading Gasoline With a Damaged Bonding Cable
You arrive at a retail station to unload 2,500 gallons of regular gasoline from a 3-compartment tanker into a 10,000-gallon underground tank. The station has a vapor-recovery system. While setting up, you find the truck's bonding cable clamp is cracked and will not grip the station's grounding post. The station attendant offers a pair of automotive jumper cables and says, 'The vapor hose is connected, so you don't need the bond.' The emergency shutoff is 60 feet away near the office, and the attendant says he will be inside doing paperwork. The station is busy with customers. The underground tank is at 85 percent capacity, and the load is 2,500 gallons.
1. Is the attendant correct that vapor recovery makes bonding unnecessary? Explain the static-ignition hazard and what must be bonded or grounded.
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No. Vapor recovery controls vapors; it does not equalize static potential between the truck and the storage tank. Static can build as product moves through hoses, filters, and piping, and a spark at the hose connection or dome can ignite gasoline vapor. The truck must be bonded to the storage tank, and grounded if the system requires it, with a proper bonding cable and clamp. Jumper cables are not an acceptable substitute: the clamp may not grip, may spark, and may not be rated for the purpose. The bond must be made before any dome cover or valve is opened and kept in place until transfer is complete and the vapor line is disconnected. The 10,000-gallon tank at 85 percent has only 1,500 gallons of ullage; a 2,500-gallon load would overfill it by 1,000 gallons, regardless of bonding.
2. What should you do before opening any valve, and what would make you stop the transfer?
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Before opening a valve: park so the truck is stable, set the parking brake, chock wheels, shut down unnecessary electrical equipment, verify the bond and ground, confirm the vapor-recovery connection, confirm the emergency shutoff is accessible and the attendant is present, and calculate ullage. Here the tank has only 1,500 gallons of room, so I would not unload 2,500 gallons; I would stop and arrange a split delivery or another tank. I would also refuse to unload unattended with the shutoff 60 feet away. During transfer I would stop immediately for any leak, odor, hose strain, loss of bond, overfill alarm, unattended condition, or emergency. A damaged bonding clamp alone is a stop-work condition until a proper replacement is available.
3. If a spill or hose rupture occurs during transfer, what is the emergency sequence?
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If a hose ruptures or a spill occurs, do not try to stop the flow with your hands or by kinking the hose. Use the emergency shutoff if it is safe and within reach; otherwise move away and call 911. Shut off the truck engine if safe, keep people away, eliminate ignition sources, and stay upwind. Contain the spill only if you can do so without exposure; gasoline vapor is heavier than air and can travel. Notify the station, your dispatcher, and the emergency responders, and do not restart transfer until the system is repaired and inspected. If the emergency shutoff is not accessible, that is a reason not to start the transfer in the first place.