What’s the Difference between FD and EI Fire Doors

The difference between FD and EI fire doors comes down to what each rating tests and the standard it is tested against. An FD rating comes from the older British Standard and confirms how long a door holds back flames and hot gases, which is known as integrity. An EI rating comes from the European standard and confirms two things, integrity and insulation, meaning the door also limits how much heat passes through to the unexposed side. So an FD door is rated on containment alone, while an EI door is rated on containment and heat resistance together. The two are not interchangeable, and treating them as equal can lead to the wrong product being specified.

That distinction matters more than ever right now. The British Standard behind FD ratings is being withdrawn from building guidance, and the European EI system is becoming the single benchmark for fire door performance in the UK. Below we explain what each rating means, where the numbers come from, why they are not equivalent and what you should be specifying for a new project.

What an FD Fire Door Rating Means

FD stands for fire door, and an FD rating tells you how many minutes a door has been shown to resist fire in terms of integrity. Integrity is the ability of the door to stop flames and hot gases passing from the fire side to the other side for a set period. The number after the letters is the time in minutes, so an FD30 door holds back fire for 30 minutes and an FD60 door for 60 minutes.

FD ratings come from BS 476-22, the traditional British Standard for testing the fire resistance of doors and other building elements. This standard was written in 1987 and has been the reference point for fire doors in the UK for decades. An FD rating on its own measures integrity only. It does not tell you anything about how hot the unexposed face of the door becomes during a fire.

You may also see the letter S added to a rating, written as FD30S or FD60S. The S confirms the door has also been tested for resistance to cold smoke leakage under BS 476-31, which is a separate test from the fire resistance test itself.

Common FD ratings you will come across on a door schedule are FD30 and FD60, with FD90 and higher available for more demanding situations. The right one depends on the fire strategy for the building and the level of protection a particular opening needs.

What an EI Fire Door Rating Means

EI ratings come from the European classification system set out in BS EN 13501-2, with the fire test carried out to BS EN 1634-1. Instead of a single FD measure, the European system separates performance into two letters.

E stands for integrity, the same containment measure described above, the ability to stop flames and hot gases for a set time. I stands for insulation, the ability to limit the temperature rise on the unexposed side of the door so that the surface stays cool enough to touch and does not set fire to anything resting against it. An EI60 door therefore provides 60 minutes of both integrity and insulation.

You will also see an E rating on its own, for example E30 or E60. An E rating covers integrity only, with no insulation requirement, so it sits closer in scope to an FD rating than a full EI rating does. There is a third classification, EW, which adds limited control of radiated heat without meeting the full insulation standard.

This is the core reason the systems differ. Under the European test, insulation is judged by the temperature rise across the unexposed face, with failure set at an average rise of 140°C above the starting temperature or 180°C at any single measuring point. An FD rating contains no such check, which is the single most important thing to understand when comparing the two.

AFS products are classified using the EI system, and you can read more about how these ratings work across our range on our fire rated products pages. We also publish individual breakdowns of each rating in our knowledge base, including EI 30, EI 60, EI 90 and EI 120.

FD vs EI: The Key Differences Side by Side

The simplest way to hold the difference between FD and EI fire doors in your head is to look at what each one tests.

An FD rating is the traditional British classification from BS 476-22. It confirms integrity, which means it stops flames and hot gases for the stated number of minutes. It does not confirm insulation, so the surface of the door can become extremely hot on the side away from the fire.

An EI rating is the European classification from BS EN 13501-2, tested to BS EN 1634-1. It confirms integrity in the same way an FD rating does, and it also confirms insulation, which keeps heat transfer through the door under control so the protected side stays far cooler.

In short, an FD rating answers one question: has the fire been contained? An EI rating answers two: has the fire been contained and has dangerous heat been kept back as well? For escape routes, protected corridors and any situation where people may need to pass close to a door during a fire, that insulation performance can be the deciding factor.

Are FD and EI Ratings Equivalent?

This is where care is needed, because it is a common and costly assumption. An FD30 door is often described loosely as the equivalent of an E30 door, and in terms of integrity performance the two are broadly comparable. They are not, however, legally synonymous, and the comparison only holds for the integrity element.

The mistake is to assume that an FD rating delivers EI performance. It does not. An FD60 door tested to BS 476-22 might only achieve an E60 result, integrity only, when assessed under the European method, because its insulation at the frame edge was never recorded. Heat transfer through the frame and the junction between leaf and frame is one of the most common points of thermal failure, and the European test scrutinises exactly that. An EI door has been proven to control it. An FD door has not been tested for it at all.

So if a specification calls for an EI rating, an FD-rated door is not a like-for-like substitute. The two ratings describe different things, and choosing on the basis of the time alone, the 30 or the 60, misses the point of the letters in front of it.

Why the FD Standard Is Being Phased Out

There is a further reason to focus on EI ratings for any new work. The British Standard behind FD ratings is being withdrawn from building guidance in England.

Following the Grenfell Tower inquiry and several reviews of building safety, the government confirmed it would move to a single European classification system and remove the BS 476 series from Approved Document B, the statutory fire safety guidance. The change is happening in stages. References covering reaction to fire were removed in March 2025, and the fire resistance standards, which include BS 476-22 for doors, will be removed on 2 September 2029. After that date, only the European EN classifications will be accepted for demonstrating compliance in new work.

In practice this means EI is becoming the benchmark, not the alternative. Doors tested only to the older standard will eventually fall outside the guidance for new projects, and manufacturers across the industry are re-testing products to the European method ahead of the deadline. Specifying EI now is the way to stay aligned with where the regulations are heading rather than where they have been.

If you want a fuller explanation of how the European classifications apply to glazed systems, our guide to the types of fire safety glass and the E vs EI distinction covers it in detail.

Which Fire Door Rating Do You Need?

The rating you need is set by the fire strategy for your building, which is usually defined by the responsible designer or fire engineer rather than chosen at the point of purchase. As a general guide, the time element (30, 60, 90 or 120 minutes) reflects how long that part of the building needs to hold back fire, and the letters reflect whether insulation is required as well as containment.

Many of the enquiries Aluminium Fire Systems receives still ask for FD30 or FD60 products and plenty of clients still refer to fire doors in those terms. When that happens, the team quotes for the EI equivalent and explains what EI stands for and how it differs from an FD rating, so you know exactly what you are being supplied and why. Where the specification explicitly calls for EI, an integrity-only FD door will not satisfy it.

Because Aluminium Fire Systems works exclusively in fire-rated aluminium, every enquiry is handled by people who deal with these classifications daily, and every completed job is backed by a compliance pack covering the relevant classification evidence. You can see the full range across our fire rated aluminium doors, fire rated aluminium windows and fire rated glass partitions.

Why Choose Aluminium Fire Systems

Fire-rated aluminium is not a sideline for us. It is the only thing we do. Every member of the team, from the people preparing your quote through to the people manufacturing the product, works in fire-rated systems specifically rather than treating it as one product line among many. As a UK manufacturer supplying direct, we cover ratings across the EI30 to EI120 range.

Our work centres on the Aluprof MB-78EI system, our go-to choice for most internal and external fire doors and screens, and the MB-118EI system for requirements up to 120 minutes. Our products carry the UKCA mark and are backed by independent third party certification through Certifire, and we work with approved glass providers including Aluprof, Pyroguard and Vetrotech Saint-Gobain.

That focus carries through to the paperwork. With every completed job we provide a customised compliance pack, giving you the classification evidence and documentation you need for the golden thread.

We work with clients across the UK in a range of sectors including: 

• Healthcare including hospitals, 
• Schools/education, 
• Commercial buildings and offices 
• And more. 

To learn more about some of the projects we’ve delivered, read our EvaBuild or WDS Ltd case studies.

If you need fire rated projects, get in touch with us today via our contact page to discuss your project.

FAQs About FD vs EI Fire Doors

About the Author

This article was written by Emma Wright, the Operations Manager at Aluminium Fire Systems. Emma oversees the core fabrication and technical output at AFS, working closely with principal designers, contractors and developers to ensure every bespoke profile matches stringent UK safety classifications. 

You can read more about the wider team on our team page, or get in touch through our contact page to discuss a project.