Together, they produce the chain reaction which results in formation of fire. In fact, the chain reaction is the 4th component that has been introduced recently to explain fire(Fire tetrahedron). It is seen as the feedback of heat to the fuel to produce gaseous fuel used in the flame. In other words, the chain reaction provides the heat necessary to maintain fire.
Coincidentally, the same elements apply for fire hazard Feng Shui. According to the Yi logic 易理, house is the fuel, wind is the oxygen, fire trigger is the heat and implicitly Tai Sui year facilitates the chain reaction.
I believe your next questions will be what are the land forms for the 4 components of fire and how do they look like? It is unfortunate and I apologize as I am not able to reveal here. But do take a close look at the recent fire incident that happened at Jurong West market. This is a classic fire hazard formation according to Naked Eye technique (形家長眼法).
If you are sharp enough, you may pose the question if any ignited objects such as stove, lighters, incense or electrical sparks suffice as the fire trigger? My answer is No. A fire trigger landform is needed. On the other hand, ignited objects are the physical cause of fire as a result of an action. Think about it they are different matters after all. That is why I always say Feng Shui is not science, it is the study of Feng 風and Shui 水 only…