What does an incendiary device primarily use to cause harm?

An incendiary device primarily utilizes a fire-producing substance to achieve its intended effect, which is to ignite and create a significant fire. These devices are specifically designed to generate heat and flames, often causing destruction to property and posing a danger to life.

The distinction here lies in the purpose and mechanism of incendiary devices, which focus on fire rather than an explosive reaction or the presence of chemicals that would cause harm through a different means. This makes fire-producing substances the core component of incendiary devices, as they are crafted to spread fire quickly and effectively, resulting in damage or injury.

Other options, although related to harmful devices, do not directly pertain to the primary function of incendiary devices, which is centered around fire production rather than explosions or chemical reactions.