Fire Plays Return Engagement Explosions and fire tore through several buildings of the M. Backes & Sons Company Fireworks plant at Wallingford, Conn., on March 29, causing damage estimated at $100,000. One employee, Michael Gust, was badly injured and taken to Meriden hospital. Two other employees were less seriously injured. Firemen heard three explosions and sped to the plant without waiting for an alarm. Flames fed by the highly combustible fireworks materials roared through the sparkler plant, a building used for making caps, and a storage building. Cause of the fire was not immediately determined. Less than four years ago an explosion and fire at the same plant killed one worker and injured several others.