Berlin (CNN) -- A chemical accident involving chlorine gas injured nearly 40 people Tuesday at a plant for security technology in Bruhl.

Of the 39 victims, seven were seriously injured, according to Markus Brachschoss, a spokesman for the local fire department. Around 300 people were inside the plant at the time of the accident.

The incident occurred when two chemicals -- sodium hypochlorite and hydrochloric acid -- came into contact, emitting chlorine gas.