What are Hazardous Chemicals? "Any chemical which is a physical or health hazard." â¢ Physical hazards - are chemical reactions that could result in a fire, explosion, and/or toxic gas release which cause physical trauma if chemicals are handled or stored improperly. â¢ Health hazards - are health effects (illness or disease) caused directly by the chemicals themselves, not an injury resulting from a reaction. All chemical materials can cause health problems under the wrong conditions.