Which of the following is NOT a category of fire hazards?

The correct answer is that thermal is not considered a distinct category of fire hazards in the same way the others are. Fire hazards are typically categorized based on the type of material or energy sources that can contribute to the ignition or spread of fire.

Biological hazards would encompass risks associated with living organisms, such as bacteria, fungi, or other microbial agents that may pose a fire risk in certain environments. Electrical hazards involve risks related to electrical systems and appliances that can cause sparks, heat, or other conditions leading to fires. Chemical hazards include flammable or reactive substances that can ignite or explode in certain conditions.

Thermal, while it relates to heat and can be a contributing factor to fire incidents, does not stand alone as a category of fire hazards within the commonly used categorizations. It is often a part of discussions surrounding the conditions leading to fire rather than a separate classification itself.