Which hazard category includes self-reactive and pyrophoric chemicals?

The correct answer is that self-reactive and pyrophoric chemicals fall under the category of Physical Hazards. This classification is based on the inherent properties of these chemicals that can cause physical harm without necessarily leading to an adverse health effect.

Self-reactive chemicals are substances that can undergo an exothermic reaction without the involvement of an external oxygen source, leading them to potentially explode or release harmful gases under certain conditions. Pyrophoric chemicals ignite spontaneously in air at or below 130°F (54°C), presenting significant risks of fire and explosion upon exposure to air.

In contrast, health hazards generally refer to chemicals that can cause harmful effects primarily through inhalation, skin contact, or ingestion, affecting health in various ways over time. Simple asphyxiants relate specifically to gases that can displace oxygen in the air but do not tend to involve reactions that present the kind of immediate physical risks posed by self-reactive and pyrophoric substances. Combustible dust primarily pertains to finely divided solid materials that can create explosive conditions when suspended in air, and does not encompass the characteristics of self-reactive or pyrophoric chemicals.