When exposed to fire as in a warehouse event, plastic IBCs containing combustible or flammable liquids can melt or burn fairly rapidly, releasing their entire contents and increasing the fire hazard by the sudden addition of combustible fuel. Rigid plastic (as high-density polyethylene) IBCs that transport and house flammable/combustibles are recommended to have clear labeling and stored within properly secured structures and according to federal regulations, such as NFPA and OSHA. Metal IBCs (as carbon steel and stainless steel) are often approved per UL 142 requirements for housing these materials long term. Accordingly, metal IBC tanks can be used for Class I materials, while rigid plastic IBCs can be used for Class II/III materials.