Labor officials in Nova Scotia want to know to why a 46-year-old quality-control technician died 18 hours after inhaling D-Malic acid at a Sepracor plant in Windsor, where a stop-work order has been issued to the laboratory, the Canadian Broadcasting Corporation reports. Three other workers at the Sepracor plant were also exposed to the compound, but did not suffer any reactions.

“The lab has been closed to performing this procedure with this material until further notice,” a Labor Department spokeswoman told the CBC. “The company has also been ordered to provide the department with their health and safety procedures, and the company is going to be carrying out an incident investigation of their own, to be completed by October 24.”

Investigators are examining protective equipment in the area where the technician was exposed to the compound, which is used in the analysis of drug ingredients. “It’s something dangerous enough that it is normally used within a fume hood. But in this particular case, as part of a larger investigation, we are looking into whether or not a fume hood was operating properly at the time,” she said.

“Sepracor has been informed that the employee had been home for several hours after leaving work in apparently good condition on October 7,” the drugmaker said in a statement. “Sepracor is unaware of any link between the employee’s work duties and the condition he reported in hospital, and is co-operating with all concerned authorities, including the Department of Labor.”