A wastewater tanker being welded at a repair shop exploded, sending the welder and a manhole cover through the roof. The welder died.

The tanker owner had agreed to provide the tanker clean and ready for welding. His driver had washed it out with a garden hose using a single manhole opening at the center of the top of the tanker.

When the tanker arrived on Friday, the welder brought it into the repair shop, "sniffed" it using a combustible gas detector and found no problem. The tanker exploded Monday morning just after the welder began the repair work.

It was clear that the tanker driver had done a poor washing job. The tanker had many baffles down its length; the driver could not possibly have seen what he was washing or reached most of the tank using a garden hose through its central opening.

Defense attorneys said the tanker had not been "sniffed," but the testimony indicated otherwise. Our analysis showed that Friday was a cool day, and that the chemicals in the tanker were not volatile enough on Friday to produce an explosive mixture. The mixture became explosive as the tanker warmed up in the garage over the weekend.