The US Chemical Safety and Hazard Investigation Board on Sept. 24 approved two final reports on accidents that killed six workers. The reports were critical of AB Specialty Silicones of Waukegan, Illinois, where four workers were killed May 3, 2019, and an Evergreen Packaging paper mill in Canton, North Carolina, where two workers died Sept. 21, 2020.The silicones plant was making a silicon hydride emulsion when a flammable vapor cloud developed and ignited, causing an explosion and fire. In addition to the deaths, a fifth employee was seriously injured. The CSB found that workers inadvertently mixed several incompatible chemical compounds that were stored near each other in nearly identical drums, generating hydrogen gas that ignited.The facility lacked an adequate ventilation system and a working alarm system, the CSB noted.
It was surprising to me that the various chemicals were all in 55-gallon blue drums. They could be easily confused, although there are plenty of ways (different staging sites, double-sign offs, ID verification) that you could stop operators from charging the wrong reagents into reactors.
I've seen this go wrong on a smaller scale. I worked in a CASE industry formulation plant where all raw materials were given a code name of two letters and four digits, and the plant staff generally knew chemicals by their internal code names rather than their chemical or trade names. The alphanumeric system helped minimize the consequences of errors because the two letters at the beginning indicated a general class such as resin, curing agent, additive, filler, etc. The too-common mistake of transposing a couple of digits resulted in the wrong resin or curing agent being substituted, not someone accidentally mixing a big pot of resin and curing agent (which is unlikely to blow up, but likely to generate a dangerously large exotherm and large amounts of noxious smoke).
ReplyDeleteI agree that the system could have been improved with additional verifications, and I think we got cocky because errors seldom caused worse consequences than a ruined batch.