Tanker Vehicles: Surge, Rollover Risk, and Outage
Colorado's Tanker Vehicles test is 20 questions with 80% to pass, and it applies to vehicles carrying liquid or gaseous cargo in tanks with an individual capacity over 119 gallons and an aggregate of 1,000 gallons or more. The exam focuses on what makes a tanker different: surge, a high center of gravity, and loading limits.
Surge and stability
- Liquid moves inside the tank. When you brake, the load surges forward; when you accelerate, it surges back; in a curve, it pushes to the outside.
- Baffles divide the tank and reduce surge, but they do not eliminate it. An unbaffled tank has the worst surge.
- A loaded tanker has a high center of gravity, so it rolls over more easily than a dry van. Slow down before curves and avoid sudden steering.
- Start, stop, and shift smoothly; abrupt inputs start the liquid moving.
Loading and unloading
- Leave outage space for expansion: never fill a tank more than 95% full.
- Ground and bond the vehicle before loading to prevent static electricity sparks, and use vapor recovery when required.
- Check dome covers, valves, and hoses before moving. A loose dome cover or open valve is a spill waiting to happen.
Worked example
You drive an unbaffled tanker half full of milk at 50 mph and need to stop for a light. Because the liquid can surge forward, the effective load on the front axle rises and stopping distance increases; the surge can also push the truck after it stops. Correct technique: begin braking earlier and more gently than in a dry van, keep a longer following distance, and avoid a hard final stop.
Braking and curves
- Brake before the curve, not in it. A tanker that is braking while turning is at high rollover risk.
- On downgrades, use a low gear and snub braking; do not ride the brakes.
- Keep the center of gravity low by not overfilling and by checking that baffles and bulkheads are intact.
Traps
- Assuming baffles stop all surge - they only reduce it.
- Filling the tank to 100% and leaving no outage.
- Taking a ramp or curve at the speed you would in a car.
- Forgetting to ground and bond before loading, which risks a static spark.