The ease of creating combustion with a solid substance, like a block of wood, depends on three factors:

Chemical composition, as outlined in the previous page, is an important factor in combustion, but mass and shape may be just as important. For example, shape is an important consideration when outlining the sprinkler protection for a warehouseIf a storage arrangement offers a more exposed surface area, there will be more space for a fire to move over burning surfaces. This is why rack storage is more susceptible to creating a larger fire than the same materials stored in a solid pile, or cubed storage, given the identical commodities. The cube has only a limited amount of surface area, but the rack storage has exposed sides on every pallet load..

Mass is also important. Basic physics tells us that mass absorbs energy, and some materials will have more massA piece of steel obviously has more mass than a piece of paper of the same shape and size. than others. When this is coupled with the fact that fires burn along surfaces, it is easy to see why some materials will "burn" more readily than others.

A simple word about mass...