LA PORTE (FOX 26) - It's a grim bottom line from the Chemical Safety Board.
Four DuPont workers in La Porte who lost their lives to toxic gas should not have died.
That finding after a seven month investigation revealed design flaws and blown safety procedures at the insecticide plant where a perfect storm of factors triggered a fatal event.
"I think the biggest take away is these incidents don't have to happen. They are preventable," said John Morawetz on International Chemical Workers Union.
In a CSB reconstruction investigators detailed how unvetted efforts to unclog pipes blocked by frozen material inadvertently caused toxic methyl mercaptan to flow where it shouldn't have.
When workers later attempted to drain waste liquid from a normally unhazardous section of pipe, vaporized methyl mercaptan escaped, creating a deadly cloud and overcoming four workers unprotected by gas masks.
"It was not a requirement for them to wear it. It had become a normal routine procedure for those folks to go out there and drain that line without wearing additional breathing protection," said Dan Tillema, lead investigator for the U.S. Chemical Safety Board.
"Sounds very clearly the procedure was not to wear it and therefore the workers were overcome very rapidly," added Morawetz.
Tillema says the evidence shows DuPont personnel disregarded toxic gas alarms and the company's management audits apparently failed to discover flaws in the plants design and production process.
"We want to know why those audits didn't identify the deficiencies we see following the accident," said Tillema.
DuPont has agreed to implement a full range of CSB recommendations before the plant re-opens.
CSB chairperson Vanessa Allen Sutherland says it's unlikely DuPont's deficiencies will result in a criminal prosecution.
In depth video from CSB: https://www.youtube.com/watch?v=YjVOJUrhrJM