A cast iron filtration strainer on the inlet piping of an isobutylene charge pump failed dramatically in the moments prior to an April explosion and fire at a chemical plant in Crosby, Texas, that killed one person and injured 30 more, according to a report released this week by Harris County's fire marshal.
Findings from the latest report checks with the previous results from investigations by the U.S. Occupational Safety and Health Administration and the U.S. Chemical Safety Board, a press release issued by plant owner KMCO states.
“The tragic incident that struck our Crosby facility last April was an accident and resulted from the sudden failure of cast iron material in a flow line,” a statement by KMCO quoted in the Houston Chronicle states.
As stated in the previous CSB preliminary report, the operational staff at the KMCO facility was engaged in making a batch of highly flammable sulfurized isobutylene, used to produce coolant and brake-fluid products.
At one point an operator walking by the batch reactor in use heard a loud “pop” followed by a whooshing noise comparable to an air hose coming off its fitting. Investigating further, the operator described seeing a white cloud of vapor hovering near the ground with three or four feet of wavy, hazy vapor lingering above it.
About four minutes later the isobutylene vapor ignited in a massive explosion. Searchers located the single fatality near the entrance of a former control room that had been all but obliterated by the blast.
Investigators later found a hole roughly three inches by 5.5 inches in the cast iron filtration strainer, also known as a y-strainer, on the inlet suction piping to the isobutylene charged pump. It’s location corresponds to where the leaking vapor was first observed.
The ignition source for the vapor explosion remains a mystery. A final report by CSB is pending.