Intumescent Strips for Fire Doors: Everything You Need to Know

The intumescent material expands when exposed to high heat, sealing gaps between the door and frame in the process. This aids in the prevention of fire and smoke entering other areas. Intumescent strips provide 30 to 60 minutes of protection against fire depending on the type used. When fire doors are frequently neglected, intumescent strips may be rendered ineffective – a typical problem in structures with numerous residents.

In this post, we’ll give an overview of industry best practices for intumescent strips, which will assist building owners and health & safety professionals in understanding their role in a passive fire protection system.

What are Intumescent Strips?

Intumescent strips, often integrated into fire doors, are designed to safeguard lives and properties from the dangers of fire and smoke. These strips are made from materials that expand significantly when exposed to high temperatures. During a fire, this expansion seals off the gaps around the door, effectively blocking the passage of deadly smoke and flames. This sealing capability is critical in containing the fire to a limited area, thereby reducing its potential to cause extensive damage. What’s more, by containing the fire, these strips provide extra time for occupants to evacuate safely.

How Effective Are Intumescent Strips?

The effectiveness of intumescent strips in fire doors is an important aspect of building safety. These strips are engineered to provide significant fire resistance, typically offering between 30 to 60 minutes of protection. This duration is important, as it allows occupants ample time to evacuate and fire services to respond.

The level of protection offered depends largely on the rating of the strip. A higher-rated strip generally provides longer fire resistance, enhancing safety. The effectiveness also depends on properly fitting intumescent strips. If not installed correctly, the strip might fail to expand as intended, diminishing its protective capabilities.

Factors such as the type of fire door, the material of the strips, and environmental conditions also play a part in their effectiveness. Regular inspections and maintenance are essential to ensure that these strips continue to function optimally over time.

Do Fire Doors Need Intumescent Strips?

It’s generally agreed that all fire doors should be reinforced with either intumescent strips, cold smoke seals, or a combination of both to give the required level of fire resistance.

Most doors, according to British Standard 476 fire safety standards, must be S-type (smoke-sealed) doors. Installing intumescent strips on a fireproof door can help the door meet these standards. A seal must restrict smoke leakage to 3 cubic metres, per hour through 1 metre of door edge.

If a door does not meet the legal definition of a fire door, fitting intumescent strips alone will not guarantee that it provides the same level of protection. While nothing prohibits you from using intumescent strips on a regular door, it will fall short of regulatory standards.

Regulations for Intumescent Strips

There are several regulations in place for intumescent strips and fire doors in the UK. Complying with these will ensure that all fire prevention installations, such as intumescent strips, are installed correctly and set up to work optimally. The main regulations incorporate the following information:

• Routine Checking of Fire Doors: For buildings above 11 metres in height, responsible persons must check all flat entrance fire doors at least every 12 months and all fire doors in communal areas every 3 months​​​​.
• Minimum Requirements for Fire Door Inspections: Fire doors, including flat entrance doors, must be considered in the Fire Risk Assessment as mandated by the Fire Safety Order. Inspections must identify any obvious damage or issues with the doors.
• Intumescent Strip Regulations: Building Regulations require that fire doors have intumescent strips. Without these strips, the door’s effectiveness in preventing the spread of fire and smoke is significantly reduced​​. The gap between the door and the frame should not exceed 3 to 4mm on the long edges and top of the door leaf. For the bottom of the door (threshold), the gap should be around 10mm for non-smoke conditions but 4mm when smoke seals are required​​.

Types of Intumescent Strips

Intumescent strips can be either ‘fire only’ or ‘fire and smoke’. The choice depends on the specific requirements of the fire door. Common sizes for intumescent strips include 10mm x 4mm, 15mm x 4mm, and 20mm x 4mm​​.

There are several types of intumescent strips, including fire-only strips, which block flames and intense heat, and fire and smoke seals, which combine fire resistance with smoke containment. Some are combined with acoustic properties, reducing sound transmission in addition to fire protection. These strips come in different materials, like graphite or sodium silicate, each with specific expansion properties to suit various fire rating requirements.

Installing Intumescent Strips

Fire door sealings are placed in the grooves of a doorframe or on the surface of a door. They are designed to expand once the ambient temperature reaches 200°C, which will typically happen within the first 10-20 minutes of a fire. Fire compartmentation can be achieved by filling gaps between the door and frame with intumescent strips that have been properly fitted.

Intumescent strips are also subject to specific installation and fitting requirements based on your structure and fire door type. For example, some doors might require a cold smoke seal to prevent injury or damage caused by smoke. However, cold smoke seals may not be necessary in situations where smoke seepage is crucial for fire detection.

How to Fit Intumescent Strips

Intumescent strips are simple to put in if the fire door has the appropriate grooves. Alternatively, you’ll need to cut grooves using a router that is identical to the width of the intumescent strip.

Once you’ve established your groove, you can measure and cut the strip to ensure that it’s an adequate width. The groove should then be inspected for dust or debris to ensure that it’s clean, otherwise, the self-adhesive back of the strip may not properly adhere to the groove. When you install the strip, check whether or not the door still closes correctly. You might need to employ a door closer for it to close correctly. If that’s the case, fire safety rules require a Grade 3 door closer or higher.

Maintenance of Intumescent Strips

Intumescent strips, like other fireproofing materials, should never be neglected. With time, intumescent strips may crack, distort, or partially detach from a door. They can also suffer harm as a result of door usage or construction repairs. As a result, they should be inspected at least once every six months for flaws or other problems that might prevent them from performing properly. Any damaged or missing strips should ideally be replaced with identical new ones of the same size, type and manufacturer as the original.

It’s critical to inspect the fire door as part of a larger maintenance program that includes inspecting hinges, locks, and other door components. The door frame must be free of cracks or holes, and the closing should be smooth. It must also have at least three hinges in good working order. This ensures that the fire strips remain effective at providing fire protection.

Fitting fire doors with intumescent strips is just a small part of an effective passive fire protection strategy. At Ark Fire Protection, we provide full fire protection services to ensure that your building has the best chance at withstanding a fire, so get in touch today to find out more about how you can keep your building safe.