At a chemical site producing melamine, an accidental explosion occurred during restart of an industrial furnace powered by both natural gas and the residual gas from other units. The filters clogged by residual gas were regularly cleaned, which necessitated installation shutdown and restart. The explosion blasted the cover off the furnace where a maintenance team was working. The cover as well as the personnel fell into the furnace (heated to 350°C). All 3 employees were killed. As a means of shortening this shutdown time, technicians had defined a rapid restart protocol that neglected the site’s safety guidelines and indications. This rapid procedure introduced previously consisted of filling the furnace with a stoichiometric mix of gas and air. Mix ignition was likely triggered by a spark emanating from an electric fan turned on by a technician a few moments before the explosion. Property damage and operating losses were estimated in the several millions of Euros.