Why don’t the NFPA and HMIS ratings always agree?
The NFPA and HMIS rating systems are targeted at different audiences. They have similar appearances and similar interpretations, but they are fundamentally different. The NFPA rating system is directed at providing immediate information to firefighters responding to a fire that may involve hazardous materials. The HMIS rating system is directed toward providing persons using chemical products with general information related to safe use of the product. The NFPA rating is primarily based on flash point, LD50 (lethal dose for 50% mortality) information, and conditions firefighters may encounter. The HMIS information uses a wide variety of acute and chronic health effect parameters, as well as the same fire and reactivity parameters used by the NFPA system. Thus, ratings are frequently different.
