Chemical hazards can be categorized as physical or health related. They involve the unintentional release of harmful substances that can damage human health or the environment. Chemical hazards affect the body through the skin, digestive system, or lungs if air is contaminated. There are three broad types of chemical hazards - flammability which involves substances that readily catch fire, reactivity where chemicals rapidly decompose or explode when heated or shocked, and health hazards where contact with chemicals causes adverse health effects. Categories of hazardous chemicals include flammable and explosive substances like gasoline, irritants to skin and lungs like acids and paint fumes, and chemicals that interfere with oxygen in the body like carbon monoxide.