Intumescent Strips FAQs | Fire Door Seal Questions Answered

Posted on: 07.11.2024

Categories: DCD News

Fire door with door closer, hinges and intumescent strips

Intumescent door seal strips are a critical component of effective passive fire safety measures. Let us guide you through the most frequently asked questions about these seemingly simple life safety products - what are they, where do you fit them, and more.

Q: What are intumescent strips?

A: Intumescent strips are items of passive fire protection. They expand when exposed to high temperatures. They are used to seal gaps around doors to prevent the spread of fire and smoke leakage.

Q: What are the different types of intumescent strips?

A: There are several types of intumescent strips - fire only or combined fire and cold smoke. They can be made of different materials, be different sizes, and come in different finishes. Each type is designed for specific fire resistance requirements and applications.

Q: What is the difference between intumescent strips and smoke seals?

A: Intumescent strips are designed to expand to seal the gap between the door and frame in the event of a fire. Some smoke seals are designed to also fill the gap but offer additional passive fire protection as they block smoke from passing through gaps. But all smoke seals do not necessarily provide fire resistance. Some fire doors may need separate fire-only seals if fitted with smoke and acoustic seals.

Intumescent stips on a door

Q: How do intumescent seals work?

A: Intumescent seals expand to differing degrees and in different ways when heated to a high temperature. Depending on the type of intumescent strip, they are used to seal off gaps and contain fire and the spread of smoke.

Q: How much do intumescent strips expand?

A: Intumescent strips can expand at different rates depending on the core material and its specific composition.

Exfoliating Graphite: This material expands multi-directionally and can achieve a high expansion ratio of up to 28 times.
Sodium Silicate: This pale-coloured intumescent material expands up to 10 times in a uniaxial direction.
Mono Ammonium Phosphate (MAP): MAP can expand up to 40 times its original size and is multidirectional.

Due to the different expansion rates, always ensure the same type of seal is fitted all the way around a door. If only one length needs replacing you must replace seals all around the whole door.

Q: Where do you fit intumescent strips?

A: Intumescent strips are typically fitted into grooves in the door or frame. They are installed on the top of the door and up both sides. On double doors, both edges of the meeting stiles should have seals fitted. At the bottom of the door, a drop seal could be installed, if necessary. Responsible persons should check applicable building regulations, the building’s fire risk assessment, and door test evidence to determine the exact requirements and placement of seals and fire door ironmongery. BS 8214 in particular gives guidance on threshold smoke seals.

Watch our video below which demonstrates the correct use of intumescent strips on fire and smoke control doors.

Q: Do fire doors need intumescent strips on the bottom?

A: No, intumescent strips are not fitted to the bottom of a door but as mentioned, refer to BS 8214 for specifics about drop seals and accompanying threshold plate as they are not always needed.

Q: What size intumescent strip do I need?

A: The size of the intumescent strip needed depends on the fire rating required and the door’s test evidence. Intumescent strips whether fire only or fire and smoke, are typically 10mm, 15mm, or 20mm in width but can span up to 40mm. The overall length is often 1050mm or 2100mm to suit the top and sides of the door. These fire door seals are often 4mm thick but can range from 2mm to 14mm. Bespoke lengths are available. Contact our team for more details.

Intumescent strip on a door

Q: Can you paint over intumescent strips?

A: Fire-only seals can be painted over if necessary. Although it is generally recommended not to as it can affect their ability to expand. Combined fire and smoke seals should not be painted over. The brush or blade smoke seal should not be covered in any way and should be replaced if it has been painted over.

Q: Are intumescent strips required on fire doors?

A: Yes, to provide effective passive fire protection, intumescent strips should be installed on fire doors. Specific requirements can vary based on local regulations and the type of building. Approved Document B (England) notes a fire doorset supplied as a complete assembly should have edge seals.