Heat release by a reacting mass, and heat transfer to the surroundings, are both important in determining the course of a combustion process. A exothermically reacting mixture has a ignition temperature assigned to it, and whether or not the reacting mixture will ignite can not depend solely on what the mixture is made up of but also on the amount of heat that is exchanged to and from its surroundings. This was recognised by Traffanel and Le Flock in 1913. When the ignition is not predominantly thermal, then the ignition may be due to chain branching.
Many ignitions have both thermal and chain-branching contributions.