Spontaneous Combustion - Mint

When a combustible substance is heated in oxygen or air, it begins to burn with a flame of its own accord. This is called spontaneous ignition, and is to be distinguished from pilot ignition. The mechanism of ignition varies significantly depending on the type and state of the substance, heating conditions, etc., but in most cases it can be explained by thermal theory based on the balance between heat generation and heat dissipation due to reaction. Therefore, the process of heat storage plays an important role in causing spontaneous ignition, and the amount of heat generated, heating temperature, and size of the sample have a large influence. In the first place, the phenomenon of spontaneous ignition does not differ depending on the heating temperature, but when the heating temperature is high, the reaction is fast and there is little need for heat storage inside, so the time to ignition is short and ignition occurs near the surface. In contrast, when the heating temperature is low, there is a greater need for heat storage, so the ignition time is long and the ignition site moves to the center. A typical example of the latter is spontaneous ignition, which occurs over a long period of time at a temperature slightly higher than room temperature when a large amount of coal or raw cotton is piled up.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

酸素または空気中で可燃性物質を加熱したとき，みずから炎をあげて燃えはじめる現象を自然発火といい，口火による発火(pilot ignition)と区別する．発火の機構は物質の種類や状態，加熱条件などによっていちじるしく変わるが，多くの場合，反応による発熱と放熱の釣合いに基礎を置いた熱理論で説明できる．したがって，自然発火が起こるためには，蓄熱の過程が重要な役割を果たし，発熱量，加熱温度，試料の大きさなどが大きな影響をもつ．もともと，自然発火の現象は加熱温度の高低で相違することはないが，これが高いと反応が早く，内部での蓄熱は必要性が薄いので，発火に至る時間は短く，また発火は表面近くで起こる．これに対し，加熱温度が低いと蓄熱の必要性が増し，そのため発火時間は長く，発火位置は中心に移る．石炭や原綿などが多量に堆積したときに，常温より少し高い温度で長時間かけて起こる自然発火は後者の代表的な例である．

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