Why Do Fire Doors Have Intumescent Seals Around the Edges?
Fire doors have intumescent seals around the edges because the seals expand when exposed to high heat, closing gaps that would otherwise allow fire and smoke to spread.
What Intumescent Seals Are
Intumescent seals are narrow strips made from materials that react to heat. Under normal conditions, they remain thin and unobtrusive.
When temperatures rise rapidly, the material expands many times its original size.
Why Gaps Are a Problem During Fires
Fire doors are installed with small clearance gaps so they can open and close normally. During a fire, these gaps can allow flames and hot gases to pass through.
Even small openings can significantly increase fire spread.
How the Seals Respond to Heat
When exposed to high temperatures, the intumescent material swells and fills the space between the door and the frame.
This expansion creates a tight seal that blocks fire, heat, and smoke.
Containing Fire Without Moving Parts
The seals activate automatically through heat exposure. No sensors, motors, or external controls are required.
This makes the system reliable even if power is lost.
Role in Passive Fire Protection
Intumescent seals are part of passive fire protection systems designed to slow fire spread rather than extinguish flames.
The expanded seal helps the door maintain its fire-resistance rating during an emergency.
