Intumescent strips are essential components in passive fire protection systems, designed to seal gaps around doors and windows to prevent the spread of fire and smoke. Selecting the appropriate strip involves understanding various factors, including the type of fire door, the specific fire rating required, and compliance with relevant building regulations.
Understanding Intumescent Strips
Intumescent strips are heat-sensitive seals that expand when exposed to high temperatures, typically above 180°C, forming a protective barrier that seals gaps between doors, frames, and windows. This expansion helps contain fire and smoke, providing occupants with more time to evacuate and reducing property damage.
Types of Intumescent Strips
There are primarily two types of strips:
Fire-Only Intumescent Strips
Description:
Fire-only strips are designed solely to expand under heat and seal the gap between the door (or window) and its frame. When temperatures rise above approximately 180°C, the strip swells to many times its original size, forming a dense barrier that restricts the spread of flames and hot gases.
Common Uses:
Installed in fire-rated doors that are not required to provide smoke resistance.
Suitable for internal fire doors between compartments where smoke control is not specified by building regulations.
Advantages:
Cost-effective and simple to install.
Highly efficient at blocking fire spread.
Limitations:
Do not prevent the passage of smoke during the early stages of a fire, which can be a major hazard in escape routes.
2. Fire and Smoke Intumescent (Combined Seals)
Description:
These strips combine intumescent material with a cold smoke seal, usually a flexible brush or rubber-like fin made from PVC or silicone. The intumescent layer activates in heat, while the cold smoke seal provides an immediate barrier against smoke and toxic gases even before temperatures rise.
Common Uses:
Fire doors on escape routes, stairwells, and corridors.
Any door separating areas where smoke containment is critical for evacuation safety.
Advantages:
Dual protection against both fire and smoke.
Meets requirements for FD30S, FD60S, and higher-rated fire doors (the “S” indicates smoke control).
Limitations:
Slightly more expensive than fire-only strips.
Requires more precise installation to ensure the smoke seal makes consistent contact with the frame.
Factors to Consider When Choosing Strips
1. Fire Door Rating
Fire doors are classified based on their fire resistance, commonly denoted as FD30, FD60, FD90, or FD120, indicating 30, 60, 90, or 120 minutes of fire resistance, respectively. The intumescent should match the fire rating of the door to ensure adequate protection.
2. Compliance with Building Regulations
In the UK, building regulations require that fire doors be fitted with appropriate strips. For instance, an FD30 door should have a minimum of a 15mm x 4mm fire strip, as per manufacturer recommendations
3. Material Compatibility
Intumescent strips are made from various materials, including hydrated sodium silicate, intercalated graphite, and ammonium phosphate. The choice of material affects the strip’s expansion rate and sealing properties.
4. Installation Method
Intumescent can be installed in different ways:
Rebated Installation: The strip is inserted into a groove routed into the door or frame.
Surface-Mounted Installation: The strip is adhered to the surface of the door or frame.
The installation method should align with the door’s design and the manufacturer’s instructions.
Installation and Maintenance
Installation Guidelines
Choose the Correct Size and Type
Measure the gap between the door or window frame and the leaf carefully.
Select a strip that matches both the fire rating and the dimensions recommended by the door or window manufacturer. Using strips that are too small may fail to seal the gap in high heat, while oversized strips may prevent proper door closing.
Rebated vs. Surface-Mounted Installation
Rebated Installation: A groove is routed into the door or frame, and the strip is inserted flush with the surface. This method is preferred for aesthetics and protection from wear.
Surface-Mounted Installation: The strip is applied on the surface of the door or frame using adhesive. While easier to retrofit, it may be more exposed to damage or paint overcoating.
Seamless Application
Ensure the strip runs continuously around the perimeter of the door or window. Any gaps or misalignments can compromise the fire-sealing ability.
Corners may require pre-formed corner pieces or careful mitering to maintain a continuous seal.
Adherence to Manufacturer Instructions
Follow the manufacturer’s recommendations for adhesive type, curing time, and environmental conditions during installation.
Do not improvise with non-approved adhesives or techniques, as this can invalidate fire ratings and certifications.
Conclusion
Selecting the right intumescent strip is crucial for ensuring the effectiveness of fire doors and windows in preventing the spread of fire and smoke. By considering factors such as fire door rating, compliance with building regulations, material compatibility, and installation methods, building owners and safety professionals can make informed decisions to enhance fire safety.
