As a spate of autumn accidents at chemical plants continues, ExxonMobil’s oil refinery at Baton Rouge, Louisiana, was hit last week by a major fire. Four workers – at least two of which belonged to a contractor firm – were critically injured, and other employees suffered minor injuries in the blaze that broke out in a compressor associated with the plant’s 18,750-bpd alkylation unit.

The workers were taken to the Baton Rouge General Burn unit, where their conditions meanwhile have been upgraded to fair or serious, and the unit is said to be operating normally with no production issues. The refinery is listed as the fourth largest in the US, with capacity to refine 502,500 bbl/d of crude oil. Its alkylation unit produces high-octane components that for premium gasoline and chemicals.

According to news agencies, the fire started as isobutane was being pumped into a line associated with the compressor to prepare for start-up. Multiple compressors are tied to the alkylation unit, so that the alkylation unit can continue to function even when the compressor is shut, local reports said. Exxon said it is investigating the cause of the incident.