Cooperative Personnel Services Firefighter (CPS) Practice Exam 2025 - Free Firefighter Exam Questions and Study Guide

The correct choice is pyrophoric material, which is characterized by its ability to spontaneously ignite in air at or below room temperature. This characteristic makes pyrophoric substances particularly hazardous, as they can combust without any external ignition source.

Pyrophoric materials react with oxygen in the environment, resulting in a rapid exothermic reaction that leads to ignition. This property necessitates specific storage and handling procedures to minimize the risk of accidental ignition. In contrast, flammable materials typically require a source of ignition to catch fire, and while they may combust at low temperatures, they do not have the same propensity for spontaneous ignition as pyrophoric materials. Reactive materials might also pose safety hazards but generally exhibit different behaviors, such as becoming volatile or releasing gas under certain conditions, rather than igniting spontaneously at room temperature. Therefore, pyrophoric materials stand out as having an autoignition temperature at or below typical environmental conditions.