In this case, a gasoline tanker rounding a curve near Sacramento rolls over onto a field. Cars parked in the field are unoccupied, but a large amount of gasoline leaks into a drainage ditch and flows toward a housing development. Several buildings are burned.

Not much was left of the tanker; aluminum melts at the temperatures achieved in a gasoline fire. But inspection of the steel manhole covers showed that at one or more of them had broken apart as the tanker rolled. We were therefore certain that the guardrails on top of the tanker had failed to protect the manhole fittings as the tanker rolled and slid to rest.

The National Transportation Safety Board (NTSB) investigated this case and came up with a completely different scenario. They concluded that a liquid level sensing device in one of the smaller holes on the manhole cover in the photo had popped off under internal pressure when the tanker struck the ground. They calculated that this sensor failed under a pressure less than 36 pounds per square inch (psi).

We tested the NTSB theory by mounting an identical sensor on a test chamber filled with hydraulic fluid. The liquid level sensor was still attached when we terminated the test at 400 psi because the gasket under the liquid level sensor had begun to leak. Gasoline tank trailers are not built to withstand such high pressures; tests carried out in the early 1980's showed that the internal pressure generated at rollover impact is less than 15 psi.

Dr. Pesuit's deposition in this case was terminated as it was about to begin when the carrier filed for bankruptcy. The case settled soon afterward for an undisclosed amount.