Intumescent Letterplate 12″ Defender Range – 30 minute rated

When exposed to fire temperatures, the intumescent material expands and swell, forming a stable, fire resistant barrier to seal the opening of the letterbox on the fire door and preventing flames and smoke from spreading through.

Fire rated intumescent letterboxes are mail slots that use intumescent materials as their primary fire protection mechanism. When exposed to fire temperatures they seal the opening and prevent flame and smoke passing through the gap on the fire door.

The typical fire ratings of intumescent letterboxes include 60, 90, and 120 minutes. The fire rating depends on the type and thickness of intumescent material used in the letterbox on the fire door and the overall design of the letterbox assembly.