Williams Olefins Incident: The Day Multiple Safety Errors Led to a Major Chemical Plant Blast- Part 2: The errors that should have been avoided

On June 13, 2013, the Williams Olefins chemical plant in Geismar, Louisiana blew up, killing two workers and injuring 167. The main cause of the explosion was an inability to control pressure building up inside of a propylene fractionator — a distillation column that separates propylene and propane.

How did the company get to the point where such a catastrophic incident occurred? It started out with a concept that seemed to make good business sense. Instead of running their two reboilers (Reboiler A and Reboiler B) that served to cool the propylene fractionator simultaneously and shutting down the process when they fouled, why not operate one at a time?  In that way, the management team reasoned, when one shows signs of fouling, just start up the other and take the original reboiler off line.  Maintenance could then be performed on the off-line unit while the process continued to run without interruption, thereby assuring higher plant output.  In order to implement such a process, the workers only needed to add a few valves that could allow one reboiler to work while the other remained idle until needed.

However, upon closer inspection, the team at Williams Olefins should have made sure that Occupational Safety and Health Administration (OSHA) Process Safety Management and Environmental Protection Agency Risk Management Program (RMP) regulations were strictly adhered to.  These regulations require that chemical process facilities conduct a Management of Change (MOC) review before initiating an equipment change 

The purpose of an MOC review is to analyze the impact of the change on safety and health, and to determine whether operating procedures need modification in order to safely accommodate the change. The OSHA and EPA regulations also require companies to properly train affected employees on the change prior to startup or implementation.

In 2001, 12 years before the deadly explosion, Williams Olefins performed an MOC to address the installation of valves on six quench water heat exchangers, including the propylene fractionator supported by Reboiler A and Reboiler B.

Williams Olefins’ MOC process required operations, maintenance, technical, environmental, safety, and project engineering departments to consider the safety implications of installing the valves. The key departmental managers provided responses to checklist questions by answering “yes”, “no” or “n/a (not applicable). The questions were designed to prompt a targeted analysis by each department. By analyzing the data from this checklist, it would be possible to design in – and understand -- any safety issues before making the change.

While MOC checklists can ensure consideration of common hazards and typical change requirements, the Williams Olefins MOC reviewers did not identify the serious overpressure hazards introduced by installing valves on the reboilers.

The goal of the MOC process was to identify and control all possible hazards presented by a process change before implementing the change in the facility. However, the issue that Williams Olefins ran into was that they failed to perform an MOC before installing and commissioning the new block valves. Instead the MOC was performed after the plant was operating with the new valves. In effect, the MOC was used as a tool to address a regulatory requirement rather than a tool to identify and then control potential process hazards.

A better, and safer approach would have been to work with a safety provider to review all possible risk scenarios involving the proposed change so that proper risk mitigation processes and tools could be implemented.  Installing block valves into a process where they previously did not exist is a significant process change that requires careful safety analysis during the MOC.

Additional safety risks

Other safety exposures were revealed by the Williams Olefins 2001 MOC:

  • The MOC reviewers indicated that the valves did not have to be car sealed open (a car seal is a simple device used to lock or 'seal' a valve in the open or closed position), which would have provided overpressure protection for the reboilers. A safety review would have revealed that installing pressure relief valves on the reboilers would have been an even safer option than car seals.
  • Reviewers incorrectly indicated that existing operating procedures were adequate to account for the new valves, even though there was no defined procedure on how to switch from one propylene fractionator reboiler to another. A robust, equipment-specific procedure detailing the steps for switching the propylene fractionator reboilers could have prevented the disaster.
  • Reviewers indicated that the change would not require a Process Hazard Analysis (PHA), a process which would have resulted in a more robust hazard evaluation option. The new valves introduced a significant reboiler overpressure hazard, and a formal PHA would have identified that hazard.
  • Based on lack of knowledge, reviewers provided incorrect responses regarding whether the new equipment met all applicable codes and standards. They indicated that the valves either met all codes and standards, or that the question was not applicable. In fact, the addition of the valves without ensuring reboiler overpressure protection for the reboilers represented a violation of American Petroleum Institute, and the American Society of Mechanical Engineers’ codes and standards.

The responses to the MOC checklist provided an early indication of the thought processes of key managers within the organization. The priority was on managing the documentation and maintenance requirements for the new valves. What was evident, based upon the checklist responses, was a lack on emphasis or concern regarding how the addition of the valves could affect the overall process.


Following the installation of the propylene fractionator Reboiler A and Reboiler B valves, Williams Olefins also performed a Pre-Startup Safety Review (PSSR), as required by process safety management regulations. While filling out this 21-question form reviewers either did not answer or failed to correctly answer key PSSR process safety questions.

PSSRs are key opportunities to verify the validity of assumptions regarding design intent, accuracy of process safety information, and proper installation and configuration of equipment. Companies should always conduct thorough and effective PSSRs before starting up.

Bringing in a safety consultant during the MOC and PSSR process would have nullified hazards that Williams Olefins unwittingly introduced into their core process.

In order to find out how some of the various mistakes that occurred over time should have been addressed and prevented, click here.