HAZMAT CDL Test 2025 – 400 Free Practice Questions to Pass the Exam

Spontaneously combustible materials are defined by their ability to ignite without the need for an external ignition source. This characteristic arises from their propensity to generate heat through oxidation or other chemical reactions, which can lead to ignition when the temperature reaches a critical point.

When discussing the other choices, it's important to clarify their relevance to spontaneously combustible materials. Igniting upon contact with water refers to a different class of materials known as reactive substances, which can react violently when they come into contact with water. Burning easily in the air without additional heat is more characteristic of flammable materials rather than specifically spontaneously combustible ones. Finally, specific packaging materials are necessary for many hazardous materials according to regulations, but this is not a defining characteristic of spontaneous combustion itself.

Thus, the ability to ignite without an external ignition source is fundamental to understanding the behavior and risks associated with spontaneously combustible materials.