MEDINA, Ohio — Investigators said Friday that a low water level caused last month's fatal explosion of an antique steam-powered tractor at the Medina County Fair, but they may never know why there was not more water cooling the boiler.

        The tractor's engine exploded when a gush of water hit overheated steel in the boiler. The July 29 blast killed five people and injured about 50 others who were hit by flying shrapnel and soot propelled across the fairgrounds.

Steam engine owner Bill Kennedy (left) and Medina County Sheriff Neil Hassinger look Friday at the damaged crown sheet of an antique steam tractor that exploded July 29, killing five. (Associated Press photo) | ZOOM |

        John Wallace, an expert in metallurgy from Case Western Reserve University in Cleveland, said the piece of metal covering the engine's coal firebox, called a crown sheet, is supposed to be cooled by a high level of water.

        With the water level low, the tractor apparently stopped on a slope, tipping the water to one side and leaving the crown sheet at the other end exposed. When the tractor moved, water sloshed back onto scorching metal and instantly turned to steam, creating so much pressure that the engine exploded.

        “I suspect there was really not quite enough water in there,” Mr. Wallace said.

        Boiler inspectors and metal experts said they do not know why there wasn't enough water in the boiler, but that the low level could have been caused by operator error, mechanical failure or a combination of the two.

        The tractor carries 375 gallons of water in reserve tanks, but the water has to be transferred to the boiler manually, said Bill Kennedy, a steam-tractor operator who was part of the investigation team.

        “You constantly have to keep injecting water into this boiler,” Mr. Kennedy said. He added that one of the refill valves was found in the open position, suggesting that someone may have been trying to refill the boiler at the time it exploded.

        Because the tractor operators died in the explosion, “we'll never know why more water wasn't injected,” Sheriff Neil Hassinger said when asked by reporters why the water level was low.

        The sheriff said the investigating team will continue to test parts of the tractor and collect information about the explosion.

        Investigators said it was unclear whether the tractor's gauges were all operating properly. State boiler inspector Donald Milan said he discovered a crack in the tractor's water gauge that could have allowed moisture into the gauge, making it hard to read.

        The engine blew up as the tractor, which was about 90 years old, was arriving the day before the opening of the fair about 35 miles southwest of Cleveland.

        The explosion took place so quickly that the safety valve, which regulates and releases the steam pressure in the boiler when the engine is operating properly, didn't have time to work, Mr. Kennedy said.

        “What you had was a flash of steam,” Mr. Kennedy said. “There's no way the safety valve could have stopped it.

        “It's like dropping a teaspoon of something in a hot skillet. It's tremendous.”

        Those killed were Cliff Kovacic, 48, who owned the tractor; his son William Kovacic, 26; family friends Alan Kimble, 46, and Dennis Jungbluth, 58; and an employee, Bryan Hammond, 18, of Homerville.
       

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