Self-inflammation

Some materials susceptible to severe oxidization are prone to self-inflammation. During oxidization, high degrees of heat accumulate exceeding oxidization and causing inflammation without external fire source. Below are examples of self-inflammation:

1- Chemical decomposition:

Some times, if materials are stored for a long time, they decompose. Decomposition leads to self-inflammation. Example: the nitrocellulose that is used in paints manufacture, needs to be stored at a particular degree of moisture; long storage lowers moisture degree, raising nitrocellulose's temperature to inflammation.

2- Chemical reaction:

Sometimes when some materials mix with each other, an inflammation occurs without outside fire source because they produce heat when mix. Example: when sodium or calcium mixes with water, temperature gets high; and water decomposes into oxygen and hydrogen making inflammation, yellowish in sodium case, and violet in the case of calcium. The addition of petroleum to white phosphor produces powerful inflammation; this is how phosphoric bombs are composed.

3- Oxygen absorption

Some cellular materials like charcoal are capable of absorbing oxygen. Temperature gets high during absorption causing self-inflammation depending on oxygen available at the location and the smoothness of charcoal that helps absorption of oxygen, speeding the rise of temperature. 

4- Proliferation and growth of bacteria

Bacteria multiply due to the increase in the proportion of moisture in organic materials such as barley, straw and sawdust or in the presence of average wet within these materials. The result is a gradual rise in the stored temperature up to inflammation level. Such process may take long course of time, relatively reaching weeks, knowing that the increase in temperature accelerates oxidization. Example: in hot countries, percentage of moisture should not exceed 12% when storing barley; otherwise, environment will become good for bacteria to proliferate. The percentage should not exceed 15% in cool countries.

5- Slow oxidization

Some organic materials such as cotton contaminated with oils gain greedy to unify with oxygen when oil dries, pushing temperature high enough for self-ignition. Some of the most important oils subject to self-ignition when used are those used to manufacture timber such as that oil used for polishing. Vegetable oils need from 4-6 hours to self-inflame after painting. Such oils are harmful if drip over sawdust in wood workshops which may cause fires.