MEDINA, Ohio – Steam experts say it was an exposed crown shield that triggered the explosion of the 1918 Case steam traction engine on the Medina County Fairgrounds July 29.
Joined by the panel of experts he had recruited to assist the investigation, Medina County Sheriff Neil Hassinger released preliminary findings of his two-week investigation Aug. 10.
The July 29 explosion killed the owner of the tractor, Cliff Kovacic, his son, William, and three others.
The explosion lifted the antique tractor 10 feet into the air, and propelled steam, hot oil, and pieces of metal almost 400 feet onto the fairgrounds.
Ten bystanders, including two Medina policemen, were badly burned in the explosion, and 40 others were injured and hospitalized.
Twisted and torn. Now the twisted and torn remains of the crown shield, once bolted securely with 4-inch long bolts to the bottom of steam tractor’s boiler directly over the firebox, sat on the table beside the experts as they attempted to explain what they knew and what they still did not know about the accident.
The crown shield, they all agreed, was the immediate cause of the explosion.
It must have become partially exposed, heated rapidly, and caused a flash of steam that, in a nanosecond, tore the crown shield loose from its bolts and sent it catapulting through the firebox and out onto the ground, while the rest of the tractor went up.
There wasn’t enough water in the boiler at the time to keep the crown shield completely covered.
Steam explosion. According to metallurgist John Wallace of Case Western Reserve University, the metal that had been exposed never attained a temperature of more than 200 or 300 degrees hotter than the part of the crown shield that had been covered with water. It had never reached a temperature hotter than 900 degrees, not nearly hot enough to melt the exposed metal.
It was the action of water touching hot metal that resulted in the steam explosion.
Dean Jager, chief boiler inspector for the Ohio Department of Commerce, said the water injectors from the supply tanks were in working condition. He said the 1-inch injector was in an open position, indicating that someone had probably been feeding water into the boiler.
Gauge cracked. There was a crack in the glass water gauge, but no real evidence as to whether it had been there before the explosion or was caused by the explosion.
Investigators found the fusible, or pop-off, plug that had been in the crown shield was still intact. The soft core had never melted out, meaning that the front part of the crown shield had been covered by water even at the time of the explosion.
Jager said ultrasonic tests indicated the metal of the crown shield was not of uniform thickness. But it’s not certain whether that played a role in the explosion, he said.
Jager is recommending steam show organizers consider requiring pre-show ultrasonic testing for all steam engines.
Still more work. There has not been time to study the boiler itself to determine its condition or to look for cracks or welds, nor to examine the piping and joints to look for possible points that might have been leaking, Jager said.
With proper water, the engine could have been driven 10 miles down the road without any problem, said steam engine restorer William Kennedy, who also served as a consultant to the investigation.
Kennedy said he did not believe that with the crew of steam tractor experts that were on hand, the fact that the Kovacic was momentarily distracted to talk with Medina policemen had any relevance to the explosion.
Why the crown shield became partially exposed is a matter of speculation that none of the investigators or experts could answer. But at some point the engine would have been positioned in a way that water that had covered the crown plate rolled back and left part of it exposed.
As soon as that happened, the explosion was going to happen.
Combination of both. Asked it the accident was the result or mechanical failure, operator error, or a combination of both, Sheriff Hassinger said he thought it was a combination of both.
No one, however, was willing to assign any weight to the degree of complicity.
What the experts did agree on was that there would have been nothing to indicate to the operators that there was a problem.
“There would have been no forewarning,” Hassinger said.
And the fact that the steam pressure pop-off valve did not go off had no relevance, because the explosion was caused by a sudden expansion of steam, not by the normal steam pressure within the boiler.
Driving a factor. Medina Fair Board Chairman Jim Biggam said he feels the extraordinary heat that was generated by the tractor being driven to the fairgrounds was a factor in the explosion.
If it had been hauled in and unloaded, then fired up, he said, it would never have gotten nearly as hot and would not have steamed out as much of the water that was in the boiler.
“We had no control of this situation,” Biggam said. “The tractor just appeared at the gate. Perhaps that is something we will have to take a look at for the future.”
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