The CSB's lead investigator, Don Holmstrom, says instruments inside BP's control room and some inside the actual unit didn't give accurate readings or didn't work at all on March 23rd.
The alarms would have alerted operators that a tank storing hydrocarbons had filled more than 100 feet past what was considered a safe level, causing an overflow and the subsequent explosion and fire.
In a report released last month, BP officials blamed workers for the accident, saying they failed to follow emergency procedures. Some of those operators and supervisors were fired as a result. Gary Beevers is the Regional Director of the United Steelworkers Union and says those workers should get their jobs back.
The company's Ronnie Chappell says the CSB's latest report contains some of the same information BP released in May and that it stands by its decision to fire workers who were involved in the operations at the Texas City refinery.
CSB investigators say they'll spend the next 4-6 weeks examining the unit's alarm system and other instrumentation to figure out why they didn't work.