Four people were injured in a fire at the Haartz Corporation complex, 87 Hayward Rd.  10:25 a.m. Wednesday morning, according to Acton Fire Department officials. 

Acton Fire Department Deputy Chief Robert Vanderhoof said an appliance inside the complex ignited, seriously burning its operator, who was transported to Mass General Hospital with the other three injured civilians.

Vanderhoof said when the fire companies arrived, there were heavy smoke conditions on the building's first and second floor, where the fire had spread. He said the fire was extinguished fairly quickly.

Vanderhoof said fire companies from Boxborough, Concord, Maynard, and Westford responded with both fire suppression and emergency medical services.