Working conditions at Mayak resulted in severe health hazards and many accidents. The most notable accident occurred on 29 September 1957, when the failure of the cooling system for a tank storing tens of thousands of tons of dissolved nuclear waste resulted in a chemical (non-nuclear) explosion having an energy estimated at about 75 tons of TNT (310 gigajoules). This released 740 PBq (20 MCi) of fission products, of which 74 PBq (2 MCi) drifted off the site, creating a contaminated region of 15,000–20,000 km2 called the East Urals Radioactive trace. Subsequently, an estimated 49 to 55 people died of radiation-induced cancer, 66 were diagnosed with chronic radiation syndrome, 10,000 people were evacuated from their homes, and 470,000 people were exposed to radiation.