Final answer:
The stage of fire development described here is the smoldering stage. During this stage, there is an unlimited supply of fuel but limited oxygen, resulting in diminished flames and the production of smoke and toxic gases.
Step-by-step explanation:
The stage of fire development described here is known as the smoldering stage. This occurs when the fire has an unlimited supply of fuel but limited oxygen. During this stage, visible flames diminish and the fire will continue to smolder, producing smoke and toxic gases, particularly carbon monoxide.