on september 7, 2017, a massive explosion in the plant's hydrogen recovery unit resulted in the release of a steam cloud which could be seen for several miles, as well as the environmental release of low-concentration hydrochloric acid. due to initial concerns about the composition of the cloud, local officials closed a section of i-75 between nearby cleveland and calhoun, as well as nearby state route 308 in charleston. during the event, seven local residents, and a plant worker were transported to a local hospital with unspecified injuries. a firefighter and four sheriff's deputies were also treated for heat-related symptoms and later released. the following day, officials from the tennessee occupational and safety administration announced a temporary shutdown of the plant pending investigation. five days later, an environmental sensor detected elevated levels of an unnamed substance prompting a shelter-in-place order for emergency workers involved in cleanup efforts within the facility.