Federal investigators from the U.S. Chemical Safety Board (CSB) now believe they know what caused the explosion: the fine plastic powder used in the manufacture of rubber products that was trapped above a suspended ceiling. CSB investigators shared the preliminary findings of their investigation at a June 18 community meeting in Kinston
"We held this meeting to brief the community on our findings to date and hear from members of the public who were affected," said CSB Chairman Carolyn Merritt, who presided at the session. When the investigation is completed the full board will convene in Kinston to issue final safety recommendations on the case.
Merritt said that CSB is "deeply concerned" by the Kinston event and a subsequent plant explosion in Corbin, Ky. that claimed seven lives.
"The dangers of explosive dust are not well known, and helping industry to understand this insidious hazard certainly will be a priority," she added.
The dust explosion occurred above an area where rubber strips were coated with moistened polyethylene powder, investigators told the audience at the Kinston High School Performing Arts Center auditorium. Although made from a plastic similar to that in milk jugs, the powder when dry is as fine as talcum and is capable of forming explosive mixtures in air, according to CSB test results made public at the meeting.
"Our testing has now confirmed that actual polyethylene powder recovered from the plant ruins is explosive when mixed with air," said CSB lead investigator Stephen Selk. He also noted the heavy damage had thus far prevented his team from determining the source of the ignition that triggered the dust explosion.
During the production process, the plant's ventilation system drew fine dust particles into the space above an unsealed, suspended ceiling, where the dust settled and built up.
CSB Investigator Angela Blair told the group that on Jan. 29, the five conditions necessary for a dust explosion were all met at the West plant: fuel, oxygen, dispersion, confinement, and ignition.
Blair explained that by installing a suspended or false ceiling years earlier, the company had inadvertently created an area where dust could accumulate out of view, and also created a space where a dust explosion could occur and spread.
It is for these reasons, Blair added, that unsealed ceilings are not recommended where hazardous dusts may be present.
Blair said investigators had recovered numerous ceiling tiles that were scorched exclusively on the upper surface, confirming the origin of the dust explosion within the overhead space. "Eyewitnesses heard a sound like rolling thunder, as a rapidly expanding chain of explosions moved through the ceiling space and literally tore the building apart," Blair noted.
The blast was so powerful it broke windows across town and shook the airport control tower several miles away. The ensuing fire burned so hot for so long, it was two days before anyone was permitted to enter what was left of the building.
The CSB so far has conducted 93 detailed interviews of witnesses to the West explosion, including plant workers and residents, and participated in or reviewed the results of 177 additional screening interviews conducted by the Bureau of Alcohol, Tobacco and Firearms.