DEER PARK, Texas (KTRK) — The US Chemical Safety and Hazard Investigation Board (CSB) released an update Wednesday on the investigation into a chemical leak that killed two people and injured others at the PEMEX Deer Park Refinery in October.

The video above is from a previous ABC13 report.

According to the CSB, two contract employees at the refinery partially opened a flanged connection on pipes containing hydrogen sulfide gas, causing the spill.

One of these workers was killed.

Two other contract workers from a separate company, working on equipment less than 250 feet away and upwind of the spill, were also affected, one of whom died from the hydrogen sulfide exposure.

About 27,000 pounds of toxic hydrogen sulfide gas was released, CSB said.

ORIGINAL STORY: 2 dead, at least 35 injured after chemical spill reported at Deer Park refinery, officials say

A lawsuit has been filed for one of the contractors, identified as 28-year-old Jose Perez.

His family, which is suing Pemex and two other companies, said his death was preventable.

The 30-page lawsuit was filed in Harris County and alleged negligence by Pemex, Shell USA and PMI Services of North America.

“(The families) cannot get their loved ones back. What they want is changes so that this never happens again. This was an event that was absolutely preventable if people would have followed procedures and safety rules,” Managing Partner at Abraham Watkins Law Firm , Benny Agosto Jr. said.

Attorney Benny Agosto Jr. representing the Perez family. He says Perez was in an adjacent unit when the release occurred. He tried to escape but passed out before he could get out.

Agosto says they have been investigating the Pemex site with their engineers.

“There was a work order that wasn’t done properly. When you do work permits, you have to go out with contractors. Contractors that started working on this pipe, which was not insulated. (It) opened up and toxic gas came out,” Agosto said.

The lawsuit accuses Pemex, PMI Services and Shell USA of a laundry list of violations, including failure to implement safe evacuation procedures and improper maintenance of equipment.

The CSB said its investigation is ongoing and focuses on several key areas, including permit-to-work procedures, energy isolation procedures, contractor management systems, emergency preparedness, communication and response systems, hazard analyzes and risk assessments, maintenance procedures, training programs, respiratory protection and remote isolation capabilities.

The board does not issue citations or fines, but issues safety recommendations.