Process Safety: When Everything That Could Go Wrong Does
Taken from AICHE.org, process safety is a blend of engineering and management skills focused on preventing catastrophic accidents, particularly explosions, fires, and toxic releases, associated with the use of chemicals and petroleum products. Process safety is often mentioned in passing during most of my courses, however, I was not aware of the large emphasis placed on process safety until I attended the AICHE student meeting. The keynote speaker addressed a process safety incident, and the raffle as well as the jeopardy game, were both based around process safety trivia questions. At the AICHE career fair, there was literally a line at every table, except the SACHE (Safety and Chemical Engineering Education) table. Judging by the nonchalant attitudes of the undergraduates, I rationalized that process safety isn’t taken seriously until an incident occurs. Nevertheless, prevention is always better than remedy. Unfortunately, the most important lessons are learned at the expense of others. In today’s post, the lessons learned from several incidents that were not as high profile as the EXXON Velazquez spill or the PEMEX LPG fire and explosion are addressed.
In 1990, in Channelview, Texas, a 900,000 gallon wastewater tank (containing process waste from propylene oxide and styrene) exploded killing 17 people and causing $100 million of damages after management failed to consider the wastewater tank as part of plant operations and removed the nitrogen purge which kept the vapor space inert. The explosion happened after the compressor was started in the presence of undetected oxygen buildup. The takeaway from this incident is to ensure that the proper MOC maintenance is followed, all chemicals that enter a wastewater tank should be treated as a chemical reaction waiting to happen, and finally all workers must be aware of the reactions that are taking place.
In 1994 at Terra Industries, four people were killed and 18 people injured after massive explosion occurred when ammonium nitrate solution was left in numerous vessels after a process shut down. After thorough investigation from the EPA, it was determined that the explosion occurred because a procedure for a safe state at shutdown or any procedure to monitor the vessels during shut down was not established. The key lesson learned from this incident was that it is important to make sure that operations procedure cover all phases of operation and a complete hazard identification step would have enable better design solutions to be identified.
In 2011, at Hoeganaes, a series of three incidents left a three individuals dead and five injured. The tragedy was due to several iron flash dust fires and an a hydrogen explosion. Addressing the first incident only, it occurred when the elevator used to transfer the powdered iron was shut down after they suspected that the elevator was misaligned. When the elevator was restarted, vibrations disturbed powder that was on the equipment resulting in a flash fire. The lessons learned at Hoeganaes are that there should have been a better understanding of the hazards and risks. The combustion test that determined iron to be a weak explosion should have been taken more seriously; being classified as a weak combustible material is not the same thing as saying it incombustible.
While these incidents were able to raise our awareness, they should have never happened. Process safety is as important as any other field and should not be put on the back burner, until when everything that could go wrong does.