Teaching safety in the chem lab
Last year Willey’s article analyzing the chemical reaction that led to the tragic explosion at T2 Laboratories in 2007 earned him the Bill Doyle Award for best paper presented at the 2011 American Institute of Chemical Engineers Loss Prevention Symposium, the second highest award in the specialized area of process safety.
T2 was a small start-up company manufacturing a gasoline additive. The process involved a large scale exothermic reaction — meaning it created lots of heat. The reaction took place in a 2450 gallon reactor vessel surrounded by cooling water. The heat from the reaction would transfer into the water, which would boil and release the heat with its steam while more cool water enveloped the reactor.
One day — December 19, 2007 — the cooling water mechanism failed. The reaction began to heat up. The heating up caused the reaction to go faster. Which caused it to heat up even more. Eventually, the temperature rose so high that the solvent in which the reaction was taking place began to decompose — another more violent exothermic reaction, which heated the system even more. And sped it up even more. As this process continued (a runaway reaction), gas built up in the reactor. When the pressure reached 400 pounds, the relief valve opened releasing the pressure. But it was already too late. The reactor exploded with the force equivalent to 1400 lbs of TNT, according to the Chemical Safety Board, which completed a report on the incident in 2009.
The graph to the left shows some of the results from the team’s efforts. They offer three scenarios: Diglyme decomposition under normal conditions, when cooling is functioning properly, diglyme decomposition under the conditions present during the accident, when the relief valve was set to 400 pounds, and diglyme decomposition under an intermediate set of conditions, where the relief valve was set to 75 pounds. “If the relief valve had opened at a lower pressure, this second reaction would not have had the initiating conditions to bring it into a runaway,” said Willey.
“The lesson to the reader is the physical demonstration that the relief device should be set to open at slightly over working pressures instead of closer to the pressure rating of the reaction vessel.” This seems like common sense, Willey admitted. The problem is that it’s not.
The two owners of T2 had undergraduate degrees in chemical engineering and chemistry, respectively. Neither of them had any training chemical engineering hazard avoidance. They both died — one from the explosion, one from a heart attack after the explosion, according to Willey.
Willey’s paper now appears as a module in the Safety and Chemical Engineering Education Program, an online resource for ChemE educators. “There are slides for professors to use, we show the development of the equations used in the modeling,” he said. Further, the example is used in Fogler’s textbook on chemical reactor design, which is used by an estimated 75% of all chemical engineering programs in the country.
When I asked Willey if this was the main area of his research he responded with the words “Runaway reactions. You know, as in Bhopal.” I’d told him earlier that I had a background in chemistry and when I didn’t recognize the words, I thought I was forgetting some essential lesson from inorganic. “Type Bhopal reaction into Google and see what comes up,” he said. Bhopal reaction disaster came up.
Willey received the Bill Doyle Award once before, for his paper “The Accident in Bhopal: 20 Years Later.” In that case it wasn’t four people who died, it was several thousand. It happened in 1984 (2 years after I was born, my weak excuse for not knowing about it) as a result of cost cutting measures which jeopardized the safety checks. Forty-one metric tons of methyl isocyanate were released into the atmosphere. Since the chemical is heavier than air, it sank to the ground after being blown out the vapor stacks and infiltrated the surrounding land and the slums that were built on it. In addition to the deaths, hundreds of thousands were exposed to the chemical resulting in serious illness.
I asked Willey how many people died in Chernobyl. That number is harder to pinpoint, as people continue to suffer from exposure related illness after that 1986 tragedy. But he put Bhopal at second worst non-war related man-made disaster in history. And I’d never heard of it. He picked up his cell phone and called his friend, “Dennis,” he said, “I’m sitting in front of a chemist who’s never heard of Bhopal.” I was kind of horrified. When he hung up after a few minutes of small talk I asked if I was unique.
“No, you’re not unique,” Willey said. “That’s the problem.”
If you’re reading this, please comment: did you know about Bhopal before? Were you taught in a chemistry or chemE class?
Photo: Aerial view of T2 Laboratories, Inc., following explosion and fire, via Wikipedia