How Do Fire Doors Work?

A standard door and a fire door may look identical, but under fire conditions, the difference between the two can be the difference between 3 minutes and 60. What creates that difference is not visible from the outside, but it comes from the seals fitted around the door, the material the core is made from, and how well the door has been maintained. The Fire Door Inspection Scheme found that 31% of fire doors in Britain were incorrectly installed from the start, and in most cases, it simply comes down to people not understanding how a fire door actually works.

So in this article, we will break down what a fire door is, how fire doors work, the components inside them, FD ratings, legal requirements, how they differ from fire exits, and how to check whether yours are compliant.

What Is a Fire Door?

A fire door is a specially constructed door that has been tested to resist fire and smoke for a set period, typically 30 or 60 minutes, in order to protect escape routes and limit the spread of damage.

Fire doors do not put out fires. They contain a fire within one compartment, which buys time for occupants to evacuate and for emergency services to respond. This containment function is what makes them so critical to building safety.

Fire doors form part of a building's passive fire protection system. They must be treated as a complete, certified assembly, not just a door leaf. The frame, seals, hinges, closers, and hardware all form part of that assembly, and all must meet the required standards.

How Does a Fire Door Work?

A fire door works through the combined action of several components that activate or engage under heat and smoke conditions. Each part plays a specific role, and none of them can be removed or replaced with a non-rated alternative without compromising the door's performance.

Intumescent Seals

Intumescent strips are fitted in grooves around the door leaf or frame. When temperatures reach approximately 200°C, a chemical reaction causes the strips to expand rapidly, often to many times their original volume, sealing the gap between door and frame. This expansion physically blocks flames and hot gases from passing through the perimeter gap. That is why the correct installation gap of 2 to 4mm is critical. If the gap is too wide, the expanding seal may not bridge it in time, and the door's fire resistance is compromised.

Cold Smoke Seals

Cold smoke seals, which are often brush-style or fin-style strips, are designed to prevent smoke from passing through the door at ambient temperatures before the fire is hot enough to trigger intumescent expansion. This is an important distinction, as smoke inhalation accounts for the majority of fire-related fatalities.

Cold smoke seals and intumescent strips are sometimes combined into a single integrated strip, known as a fire and smoke intumescent strip. In other cases, they are added separately via a batwing seal fitted to the frame.

Self-Closing Devices

A fire door is only effective when it is closed. Self-closing devices, typically overhead hydraulic closers, ensure the door returns to its frame automatically after every use, regardless of whether an occupant remembers to close it.

Electromagnetic door holders are a common alternative used in busy corridors. These hold doors open for ease of movement but are wired directly to the fire alarm system. When the alarm activates, the holder releases, and the door closes immediately. The minimum power standard for self-closing devices is EN3 per BS EN 1154.

Fire-Rated Core and Hardware

The solid core of a fire door, which may be made from timber, particleboard, gypsum, steel, or vermiculite composite, is engineered to resist heat for the door's full rated period.

All hardware must also be fire-rated. This includes a minimum of three fire-rated hinges to bear the door's weight and withstand heat, along with a fire-rated latch or lock and intumescent material behind the handle and latch box. Where glazing is required, fire-resistant glass with certified glazing tape must be used. Standard glass will fail rapidly under direct heat and cannot be substituted. 

Fire Door Ratings

Fire door ratings indicate how long a door has been tested to withstand fire. In the UK, the standard classification system uses the prefix "FD," which stands for Fire Door.

FD30 provides 30 minutes of fire resistance and is the most common rating. It is typically used in residential properties and lower-risk commercial premises.

FD60 provides 60 minutes of resistance. This rating is required in higher-risk environments such as high-rise residential buildings, schools, and hospitals, where longer evacuation times are needed.

FD90 and FD120 provide 90 and 120 minutes of resistance, respectively. These ratings are used in industrial or high-hazard environments and are rarely found in standard commercial or domestic settings.

The suffix "S" indicates that the door is also rated to restrict cold smoke. An FD30S or FD60S door carries certified smoke seals in addition to its fire-resistance rating.

The correct rating for any specific building is determined by a fire risk assessment. It is not a matter of personal preference or general guidance. If you are unsure which rating your building needs, Emerald Doors carries a full range of certified Fire Doors across all ratings, covering residential, commercial, and industrial requirements, so you can find the right door once your assessment is complete.

Where Are Fire Doors Required by Law?

In England and Wales, fire door requirements are governed primarily by the Regulatory Reform (Fire Safety) Order 2005. Under this legislation, a "Responsible Person," which may be a building owner, employer, or manager, is legally required to ensure that appropriate fire doors are installed, maintained, and inspected.

Fire doors are legally required in the following locations:

• All non-domestic premises, including offices, retail spaces, hospitality venues, schools, and hospitals
• Common areas and flat entrances in blocks of flats and houses of multiple occupation (HMOs)
• Domestic properties with three or more storeys, specifically any door that opens onto a stairwell

The exact number and placement of fire doors are determined by the building's fire risk assessment, which should be carried out by a competent person. Once you know what your building needs, finding the right door becomes much simpler. Emerald Doors supplies certified Fire Doors for both domestic and commercial properties, so whether you are fitting out a family home or a commercial premises, you can find a compliant option in one place.

Is a Fire Door the Same as a Fire Exit?

A fire door is an internal door fitted between rooms or corridors. Its purpose is to compartmentalise fire and smoke, preventing either from spreading from one area to another. A fire exit is a final exit door that leads directly outside the building and is not typically fire-rated.

Take a hotel as an example. In most hotels, the individual guest room doors are not certified fire doors. The fire doors are the corridor doors leading to the stairwells. This is a widely misunderstood point that building professionals and fire service personnel regularly highlight.

Fire doors must never be propped open, as doing so removes their ability to contain fire and smoke. Fire exit doors, by contrast, can be held open because they do not serve a compartmentation function.

How to Check If Your Fire Door Is Working Properly

Under UK legislation, fire doors must be inspected at least every six months, or more frequently in high-traffic areas. These inspections should be carried out by a competent person. However, building users can also perform basic visual checks at any time.

Key checks to carry out include:

Certification: Look for a label or plug on the top or hanging edge of the door. This confirms the door has been third-party certified, for example, standard by BWF Certifire, BM TRADA Q Mark, or LPCB.

Gap tolerance: The gap between the door and frame on all sides should measure 2 to 4mm. Any wider and the seals may not perform correctly.

Seals: Intumescent and smoke seals should be undamaged, fully seated in their grooves, and must not be painted over.

Self-closer: The door should close fully and latch from any open position without any assistance.

Hardware: Hinges, latch, and handle should be undamaged and correctly fitted.

Any door with a painted-over label, missing seals, or that has been propped open should be treated as non-compliant and addressed without delay.

Why Emerald Doors Is Your Trusted Source for Certified Fire Doors

Fire doors work because of a complete system: intumescent seals, cold smoke seals, self-closing devices, fire-rated hardware, and a tested core. Each element must be present and correctly installed. The right FD rating must match the building type, as determined by a fire risk assessment. And once installed, fire doors must be maintained and inspected regularly to remain legally compliant.

Emerald Doors supplies certified fire doors for both residential and commercial properties across the UK. Whether you need a standard fire door or a compliant solution for a commercial building, their range covers the full spectrum of requirements. Browse the full selection of Fire Doors to find a door that meets your building's specific needs.