All around us, there is air. Air has mainly three kind of molecules; nitrogen, oxygen and carbon dioxide, and the approximate ratio is 75% nitrogen, 24% oxygen and 1% carbon dioxide. The molecules have some kind of reaction in some substances. For example, most metals corrode or oxidize when in contact with oxygen. Global warming is caused by an increase in carbon dioxide. An increase in carbon dioxide increases the amount of solar heat that reaches the earth. Nitrogen doesn’t have a reaction with other substances as it is an inert gas. This is the case when talking about reactions at room temperature.
If the temperature around the molecules becomes higher than room temperature, the molecules react with some substances more easily. Even nitrogen has some reactions. For example, iron is nitrided by nitrogen when the temperature reaches more than 600℃. Iron creates some nitrides (Fe2N, Fe3N, Fe4N…)on its surface by coming into contact with nitrogen at a high(more than 600℃) temperature. Of course most of people don’t know about it as we can't see the phenomena in our daily life. But this is an important reaction for iron and some metals, because even on the surface, the ration of increasing nitrogen affects some kind of mechanical properties, for example corrosion property.
Propane gas is flammable while charcoal does not catch fire easily. Even if it succeeds the charcoal fire doesn't continue to burn easily. What is the difference between them? Burning is the phenomena that occurs when a substance is combined with oxygen. Propane gas is a gas, of course, and it easily mixes with air. The contact between propane gas and air has a high density because they are both gases. It’s the reason that propane gas catches fire more easily in the air than charcoal. On the other hand, charcoal is solid and contact with the air occurs only on the surface. So, the difference between propane gas and charcoal is the contact area with the air. The bigger the contact area is, the easier the substance catches fire.
The above is an explanation why charcoal is slow to catch fire, but it does not explain why charcoal catches fire. It needs to take advantage of a high temperature mixed with a substance and a large amount of air. A high temperature promotes the combination between a substance and oxygen. And the creation of fire causes a chain reaction because of the heat generated in the reaction. If the temperature remains higher than the point of fire, the fire continues to burn.
The above is an explanation why charcoal is slow to catch fire, but it does not explain why charcoal catches fire. It needs to take advantage of a high temperature mixed with a substance and a large amount of air. A high temperature promotes the combination between a substance and oxygen. And the creation of fire causes a chain reaction because of the heat generated in the reaction. If the temperature remains higher than the point of fire, the fire continues to burn.
There have been some incidents of propane gas explosions. For example, when nobody knows, it happens when a room is filled with propane gas. In generally, when a fuel gas and air mix, there is a suitable rate of explosion, even if only a small amount of firing reaction occurs an explosion transmitting the heat surrounds the gas. There is a limit to the size of explosion for some gases. There is less chance of an explosion from a leak of propane gas, and if only a part of the density of propane gas is high, the explosion will be on a small scale. If the air of a room puffs out and the density of propane gas is rather high, an explosion won’t happen because of a shortage of air density.