Loading and Unloading Tank Vehicles
The loading and unloading domain tests the sequence that prevents fire, static ignition, and overfills. The exam cares about order of operations and about who is present.
Grounding, bonding, and sequence
Static electricity builds as product flows. Bond the trailer to the loading rack or receiving tank, then connect the hose, then open valves. Keep the bond connected until hoses are disconnected and domes closed. Bonding after the product starts moving defeats the purpose.
Attendance and control
- A tank vehicle loading or unloading hazardous materials must be attended by a qualified person who stays within the required distance and can shut off the flow.
- Set the parking brake, chock wheels, and shut off the engine unless the pump requires it.
- Know where the emergency shutoff is at the rack and on the trailer.
- Confirm the product matches the tank and the paperwork before opening anything.
Top versus bottom loading
Top loading drops product into the dome; the fill pipe must reach near the bottom to limit splashing and static. Bottom loading fills through the API adapter at the base and usually includes vapor recovery. Either way, watch the gauge and never rely on the automatic shutoff alone.
Worked example
A driver connects the hose first, then attaches the bonding cable. Product starts flowing and a static spark ignites vapor at the dome. The error is sequence: bond first, then hose, then flow.
Traps that cost marks
Bonding after the hose is connected. Leaving the vehicle unattended "for a minute." Trusting the overfill sensor without watching the gauge. Relying on trailer spring brakes without chocking. Skipping the paperwork and product check.