A Guide to Intumescent Strips

A Guide to Intumescent Strips

Intumescent strips are specialized materials commonly used in fire protection systems, particularly in doors and windows, to help contain or limit the spread of fire. When exposed to heat, these strips expand (intumesce) to seal gaps, preventing the passage of smoke, heat, and flames. Here’s a comprehensive guide to understanding intumescent strips, their purpose, and how they are used.

1. What Are Intumescent Strips?

Intumescent strips are typically made from a combination of chemicals and resins that react to high temperatures. They are often inserted into door frames, window frames, and other openings as a passive fire protection measure. When exposed to heat or flames (usually above 200°C or 392°F), the material expands, filling gaps and sealing spaces that might otherwise allow the fire or smoke to pass through.

2. How Do Intumescent Strips Work?

The primary function of intumescent strips is to act as a fire barrier by swelling up when exposed to heat. The expansion is typically several times the original size, forming a dense char that is highly resistant to fire. This sealing action blocks the passage of smoke, heat, and toxic gases, improving the fire resistance of doors, windows, and other openings.

Key steps in the process:

• Heat Exposure: When the temperature around the strip reaches a critical level, typically above 200°C (392°F), the strip begins to expand.
• Expansion: The materials inside the strip, usually containing a mix of graphite or ammonium phosphate, begin to chemically react, causing the strip to expand.
• Sealing Gaps: As the strip swells, it tightly seals the edges of doors or windows, preventing the spread of fire or smoke through the opening.

3. Applications of Intumescent Strips

Intumescent strips are versatile and are used in various applications to enhance fire protection:

• Fire Doors: One of the most common uses, where intumescent strips are fitted around the edges of fire doors to provide a tight seal when exposed to heat. This helps to prevent smoke and flames from moving between rooms in the event of a fire.
• Windows: In fire-rated windows, intumescent strips are used around the frame to block heat and smoke transfer.
• Ventilation Ducts: Strips are used around ventilation ducts or openings to contain the fire within a room, preventing it from spreading via air circulation systems.
• Fire Rated Closures: They are also used in fire-rated closures, including elevator shafts, hatches, and other penetrations through fire-rated walls or ceilings.

4. Types of Intumescent Strips

Intumescent strips come in various forms depending on the material, design, and application needs. Common types include:

• Solid Strips: These are simple, solid bands or strips of intumescent material that are inserted into gaps around doors or windows.
• Foam Strips: Some intumescent strips are designed as foamed materials, which expand more dramatically and create a larger seal.
• Pre-formed Gaskets: These are strips that are pre-moulded into specific shapes and sizes for particular types of doors or frames.

They can also be produced in different sizes, depending on the requirements of the door or frame and the level of fire protection needed.

5. Performance Ratings and Standards

Intumescent strips are subject to rigorous fire testing and must comply with national and international fire safety standards. Some of the most commonly referenced standards include:

• BS 476-22: The British standard for fire resistance of non-loadbearing elements, such as doors and windows.
• EN 1634-1: A European standard for fire resistance testing of door and shutter assemblies.
• NFPA 252: A standard from the National Fire Protection Association (NFPA) in the U.S. for fire tests of door assemblies.
• UL 10C: The Underwriters Laboratories standard for fire-rated doors in the United States.

These standards determine how long a door or window can withstand fire exposure before it fails. The intumescent strip’s ability to create a tight seal plays a key role in contributing to this fire rating.

6. Installation of Intumescent Strips

The correct installation of intumescent strips is crucial for their effectiveness. Improper installation can compromise the fire resistance of doors and windows.

Key considerations for installation:

• Door Edges: Intumescent strips are typically applied along the edges of fire doors, where they meet the door frame. They may be fitted in grooves or applied to the door frame itself.
• Window Frames: For windows, the strips are often placed around the frame, particularly along the edges where the glass meets the frame.
• Correct Sizing: Intumescent strips need to be the correct size for the gap or frame they are meant to seal. Gaps that are too large can compromise the strip’s ability to expand properly and seal the space.
• Seamless Coverage: Ensure the entire perimeter of the opening is covered with the intumescent strip, leaving no gaps where smoke or flames can pass through.

7. Maintenance and Inspection

Intumescent strips should be inspected regularly to ensure they have not been damaged or degraded. The expansion capability of these strips is a one-time reaction, so if they are damaged or have been exposed to high heat, they will not function properly in a future fire event.

Key maintenance tips:

• Visual Inspections: Check for cracks, tears, or gaps in the strips.
• Test for Proper Functionality: If a door or window is not sealing properly, the intumescent strips may need to be replaced.
• Replace Expired Materials: Over time, intumescent strips may lose their effectiveness. Always replace them according to the manufacturer’s recommendations.

8. Benefits of Intumescent Strips

Intumescent strips provide a variety of benefits in fire safety, including:

• Improved Fire Resistance: They significantly enhance the fire resistance of doors, windows, and other openings.
• Easy Installation: Many intumescent strips are easy to install and can be retrofitted into existing doors and windows.
• Smoke Containment: Besides heat and flame protection, these strips help in containing smoke, which can be just as hazardous as fire.
• Cost-Effective: They are generally a cost-effective way to upgrade fire protection in buildings without major structural changes.

9. Limitations

While intumescent strips are highly effective in many fire scenarios, they do have limitations:

• Single-Use: The strips only work once when exposed to heat. After the fire, they must be replaced.
• Not Suitable for All Openings: They are typically used for smaller openings like doors and windows, but may not be suitable for larger gaps or where a more substantial fire barrier is needed.
• Limited by Design: The effectiveness of an intumescent strip depends on the correct installation and compatibility with the surrounding materials.

Conclusion

Intumescent strips are a simple yet highly effective method for enhancing fire safety in buildings. When correctly installed, they provide a critical barrier against smoke, heat, and fire spread, helping to protect occupants and reduce property damage during a fire. Regular inspection and maintenance are essential to ensure that they function properly when needed.

If you’re involved in fire safety or construction, it’s essential to select the right type of intumescent strip for your application and ensure it meets the necessary standards for your region or industry.