In this exclusive series by Chem.Info, we’re taking a look at some of the worst case scenarios that can happen when working with hazardous chemicals and asking: Do you know what it takes to survive?
The scenario: You’re an operator of a batch reactor. Outside, where the feed-tanks are located, temperatures have dropped to an extreme, once-in-a-decade low. Inside, you’re ready to add a catalyst to your batch.
You hit the button, and the catalyst goes into the batch – but nothing happens. You think it’s odd, but most likely, the reaction is happening slowly because this catalyst does not get used a lot, and it might be old. So, you hit the button again. Still no reaction.
You don’t want this batch of chemicals to go to waste. So, what can you do to get this reaction going? (Careful! The wrong answer could blow the roof off.)
- Hit the dispense button a few more times. Adding more catalyst, which could just be old and not as strong anymore, might kick-start the reaction.
- Do nothing. Letting the batch of chemicals sit could gradually heat it up — although this might take hours, and we have a schedule to keep.
- As the batch card specifies, preheat the mixture in the reactor using the heat jacket, a bit like pre-heating an oven. After the temperature is right, add the catalyst.
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C. Preheat the batch using the heat jacket and then add the catalyst.
This exact situation once played out at a specialty chemicals plant in Toronto. After adding catalyst to a batch of chemicals and not getting a reaction, an operator continued to dispense catalyst – adding eight to 10 times the amount required. At the time, he thought that the catalyst was just old or weak and that more was needed. But really, it wasn’t working as well because it was so cold, and he had not pre-heated the batch to the specified temperature.
When there was still no reaction, the operator eventually heated the reactor. Suddenly, rather than getting the reaction going slowly, all of the extra catalyst set off a runaway reaction that caused the reactor to over-pressurize. Although the rupture disk vented, it was not enough and the resulting reactor failure blew a portion of the roof off of the building, releasing toluene diisocyanate, xylene and other reactants into the air over downtown Toronto. Luckily, no one was injured in the incident, but part of the city, including a hospital, had to be evacuated for hours. The city revoked the company’s operating permit, and production of those materials had to be transferred to a plant in the U.S.
Special thanks to Scott Harris, a chemical safety expert and director of EHS Advisory Services for UL Workplace Health & Safety, who contributed to this piece! If you're a chemicals safety expert and want to contribute a "Worst Case Scenario," we'd love to hear from you! Please email Meagan Parrish: firstname.lastname@example.org.