What is generally considered a physical hazard in the context of hazardous materials?

In the context of hazardous materials, a physical hazard refers specifically to materials or situations that pose risks due to their inherent physical properties. The option relating to materials that can cause fires or explosions directly aligns with this concept. Flammable gases, for instance, are physically hazardous because they can ignite easily under certain conditions, leading to fires or explosions that can endanger personnel and property.

This definition encompasses the potential danger that such materials present in laboratory settings, particularly where open flames or other sources of ignition might be present. Understanding this classification is critical for implementing appropriate safety measures when working with these materials.

The other options address different aspects of hazards. For instance, a toxic chemical pertains to health hazards, as it can adversely affect living organisms upon exposure. A substance harmful to the environment relates to ecological hazards rather than immediate physical dangers. Lastly, a chemical with low evaporation rates may suggest stability and less immediate risk in terms of fire or explosion but does not inherently categorize it as a physical hazard.