Generally speaking, the requirement for intumescent seals or gaskets are a function of the individual manufacturers’ listing.
Intumescent products are typically used for a smoke and fire barrier on wood doors and are activated by heat.
Given the basic properties of steel (e.g. it expands when exposed to heat), seals or gaskets are not required on steel doors.
Intumescent seal are specially designed weather stripping which expands when exposed to heat and fills the voids between two surfaces (the door and door frame) creating a fire seal.