Question 663 Deck Safety

The correct answer is C) chemical action within a substance. Spontaneous combustion occurs when a substance undergoes exothermic chemical reactions, generating enough heat to ignite the material without an external heat source. This happens when a substance, such as oily rags or hay, undergoes a slow oxidation process that builds up heat within the material until it reaches the ignition point. The chemical action within the substance is the root cause of spontaneous combustion, not an external heat source (A), or heat conduction through a wall (B). The other options, while possible causes of ignition, do not accurately describe the mechanism of spontaneous combustion, which is the key focus of the question.