When it comes to fire safety in buildings, doors play a critical role in preventing the spread of fire and smoke. Intumescent strips and smoke seals are small but essential components of a fire door assembly – yet they’re often misunderstood or overlooked.
In this guide, we explain what intumescent strips and smoke seals do, how they work, and why they’re vital for fire safety compliance, particularly within a professional fire risk assessment.
What Are Intumescent Strips?
Intumescent strips are fire-resistant materials fitted into the edges of fire doors or door frames. Under normal conditions, they remain dormant and unobtrusive.
When exposed to high temperatures during a fire (usually around 200°C), the material expands rapidly, often up to 20 times its original size.
What Do Intumescent Strips Do?
When activated by heat, intumescent strips:
- Seal the gap between the door and the frame
- Prevent flames and hot gases from spreading
- Help maintain the door’s fire resistance rating (e.g. FD30 or FD60)
- Slow the spread of fire, allowing more time for safe evacuation
Without properly installed intumescent strips, a fire door may fail in a real fire.
What Are Smoke Seals?
Smoke seals are usually brush or rubber seals fitted to the edges of fire doors, often alongside or combined with intumescent strips..
Unlike intumescent strips, smoke seals are designed to work at normal temperatures.
What Do Smoke Seals Do?
Smoke seals:
• Restrict the movement of cold smoke around door edges
• Reduce the risk of smoke inhalation (the leading cause of fire-related fatalities)
• Protect escape routes from filling with smoke and keeping them clear for occupants to escape
• Help contain smoke to the room of origin
Smoke spreads faster than fire, making smoke seals particularly important in corridors, stairwells, and protected escape routes.
Intumescent Strips vs Smoke Seals: What’s the Difference?
| Feature | Intumescent Strips | Smoke Seals |
| Activates when | High heat / fire | Normal conditions |
| Primary purpose | Blocks fire & hot gases | Blocks cold smoke |
| Required on a fire door | Yes | Often required, depends on premises use |
| Visible day-to-day | No | Yes |
In most modern buildings, both are required to meet current fire safety standards.
Are Intumescent Strips and Smoke Seals a Legal Requirement?
In many cases, yes.
Under the Regulatory Reform (Fire Safety) Order 2005, the Responsible Person must ensure that ‘routes to emergency exits from premises and the exits themselves are kept clear at all times’. Ensuring fire doors and their components are properly installed and maintained is a key element to keeping routes clear from smoke and fire in an emergency
Fire doors are tested and certified as complete systems. Missing or damaged strips and seals can result in:
- Fire door non-compliance
- Failure during a fire
- Enforcement action from fire authorities
- Increased risk to life
These issues are frequently highlighted during fire risk assessments.
Common Problems Found During Fire Risk Assessments
Fire risk assessors commonly identify:
- Missing intumescent strips
- Damaged or worn smoke seals
- Incorrect strip size for the door’s fire rating
- Strips painted over, reducing effectiveness
- Excessive gaps around the door
Any of these defects can seriously compromise fire safety and should be addressed promptly.
How to Check if Your Fire Doors Are Compliant
You should ensure that:
- Intumescent strips are fitted to all fire doors
- Smoke seals are continuous and undamaged
- Door gaps are do not exceed 4mm
- Doors close fully and latch correctly
- No unauthorised alterations have been made
A competent fire risk assessor will review all of this as part of a full assessment and provide clear recommendations.
Book a Fire Risk Assessment – Get a Free Quote
If you’re unsure whether your fire doors meet current fire safety requirements, a professional assessment can provide clarity – and peace of mind.
At Fireriskassessments.com, we deliver clear, practical, and fully compliant fire risk assessments for residential, commercial, and mixed-use buildings across the UK.
Get a free, no-obligation quote today
Frequently Asked Questions (FAQs)
Do all fire doors need intumescent strips?
Yes. Intumescent strips are essential for a fire door to achieve its certified fire resistance rating and are required in most buildings.
Are smoke seals mandatory?
In many buildings, yes — particularly where smoke control is critical, such as escape routes, stairwells, and multi-occupancy properties.
Can fire doors work without smoke seals?
A fire door may still resist fire without smoke seals, but it will not prevent the spread of cold smoke, significantly increasing risk to occupants.
Can intumescent strips be painted over?
No. Painting over intumescent strips can stop them from expanding correctly, rendering them ineffective.
How often should fire doors and seals be checked?
Fire doors should be checked regularly, with formal inspections at least every 6–12 months, depending on building type and usage.
Will a fire risk assessment identify issues with fire doors?
Yes. A professional fire risk assessment will identify missing, damaged, or non-compliant intumescent strips and smoke seals.