Tanker Vehicles: Surge, Outage, and Stability
Maryland's Tanker Vehicles domain tests the physics of liquid loads: surge, high center of gravity, and stopping distance. Tanker questions often ask why a smooth-bore tank behaves differently from a baffled tank.
Surge and stability
Liquid moves when the tank moves. A smooth-bore tank has no internal barriers, so the liquid surges front-to-back and side-to-side; baffles and bulkheads reduce but do not eliminate surge. A high center of gravity increases rollover risk. Slow down before curves, steer smoothly, and brake early and gently. Do not use sudden steering or hard braking with a partial load. Keep the outage, the empty space above the liquid, to allow expansion; never fill the tank completely.
Loading and inspection
Check dome covers, valves, hoses, and placards. Ground and bond the vehicle before loading flammable liquids. Top loading and bottom loading have different hazards; follow the terminal's procedures. Know the tank's gross weight limits and axle distribution. After loading, check for leaks and secure the dome.
Worked example
A 6,000-gallon tank is loaded to 98% capacity. The outage is 2% of 6,000, or 120 gallons. If the driver fills to 100%, there is no expansion space, and liquid can escape through the dome or damage the tank as it warms.
Traps
Filling to the top; skipping grounding; braking late in a curve; assuming baffles stop all surge; not checking dome covers; and forgetting that a partial load can be more unstable than a full one.