Hazard Class: 4.1 Molten Sulfur is a FLAMMABLE SOLID and a fire and explosion risk above 450 oF (232 oC). Sulfur is a COMBUSTIBLE SOLID. Use water spray to fight fires and to keep fire-exposed containers cool. POISONOUS GASES ARE PRODUCED IN FIRE, including Hydrogen Sulfide, Sulfur Dioxide and Sulfur Trioxide.