Textron Aviation has been issued a citation by the Occupational Safety and Health Administration for failing to protect employees from autoclave explosion hazards in a December 2019 blast in Wichita, Kansas, that injured 15 workers and contractors.
The company faces $13,454 in penalties from the federal agency.
A 64-foot tall industrial autoclave operating at 90 pounds per square inch pressure separated suddenly at Textron’s East Campus, Building 36, Plant 3, the citation states. That release of pressure caused extensive damage throughout the facility.
“As the pressure in the autoclave built, the head suffered a catastrophic thermal fatigue failure, which resulted in an explosion which critically injured 15, exposing employees to amputation, broken bone, concussion, crushing, laceration, and struck-by hazards,” the citation reads.
Measures to correct this hazard in future suggested by OSHA included closer adherence to existing inspection and operating standards established by the American Petroleum Institute, the American Society of Mechanical Engineers and the National Board Inspection Code.
The pressure inside the autoclave at the time of the accident was less than it takes to inflate a tire mounted on a big rig, Fire Chief Douglas J. Williams with Sedgwick County Fire District 1 told the county board of commissioners in an after-action report.
“We were very, very lucky that this happened during a shutdown period,” Williams said. “The large number of employees that would normally have been there were home for the holidays. Those injured were maintenance personnel and other contractors.”
Initial reports indicated that a ruptured nitrogen line was the cause of the blast. Those reports were incorrect, Williams said.
The blast hurled a 2-ton piece of the spherical autoclave more than 630 feet, taking the corner off a neighboring building in the process. As for the rest of the autoclave, it tried to climb out of a four-foot deep pit dug to protect against exactly what happened.
“The pit is there to prevent the autoclave from rolling across the floor if this occurs,” Williams said. “Even so, it shoved the pit wall and a 12-inch concrete floor on top more than eight feet back from its original position.”
The blast blew off the building’s roof, bringing the trusses and other debris down on top of the autoclave.
The first report of the blast reached 911 dispatchers at 8:02 a.m., Williams said.
The first fire officer on the scene established an incident command. Shortly after that, it was expanded to a unified command that brought the leadership of the various agencies into the command structure.
“We pulled the department heads — health department, sheriff and others – into the command van at one time to form a single command team,” Williams said.
But in those the first critical minutes after the blast, the mission was dictated by training and experience – isolate, evacuate and figure out what happened. Division Chief Tony Tracy was designated rescue group coordinator and initiated the first reconnaissance of the scene.
“The first six units that arrived were assigned to get everybody out, establish a perimeter to keep everyone back and conduct a recon to figure out the situation,” Williams said.
At 8:14 a.m., dispatches ordered the hazardous materials unit to the scene. Even though nitrogen is inert rather than toxic, Williams said the concern was about other critical operations in the plant that might have been upset in the blast.
By far the biggest upset was the giant autoclave in Building 36-C, used to compress composite materials together. When built in 1984, the ruptured autoclave was the biggest in the state. Even today it remains the largest of at least eight autoclaves in use at Beechcraft.
“When the autoclave is filled with nitrogen, they heat it,” Williams said. “Nitrogen expands 700 times when heated, building pressure inside the autoclave. That heat and pressure is used to bond composite materials used to make aircraft.”
However, rather than thousands of pounds of pressure, the autoclave’s normally operates at between 90 and 120 psi. Volume rather than extreme pressure created the problem.
Photographs show the autoclave split open along its diameter where the two halves can be opened and then resealed. Although the two halves only appear ajar, the pressure released demolished at least 20 percent of the three-building unit at Beechcraft designated Plant 3.
Outside, the large tanks of nitrogen gas used to operate the autoclave toppled and collapsed. Inside, debris that went through the wall just missing the main natural gas line, Williams said.
“Had this been hit and breached it would have been a different event,” he said. “It would have been a fire event in addition to the damage done.”
Also notable amongst the debris was a 20-foot-long piece of 10-inch iron that went through the roof of 36C and landed in the building next door, he said.
“Had this been a normal workday that alone would have injured half a dozen people,” Williams said.