Lindab Thor Duct ® is one of the world’s leaders in design and manufacture of fire duct and compliance with EN safety standards. Our Chief Technical Officer, Michael Renaghan, is a thought leader in the industry and regularly advises Consultants, Specifiers, and M&E Contractors on general and specific issues in relation to fire ducting.

Here are the top questions on fire duct and issues relating to insulation, large duct, BS and EN. 

Q. Why can’t I just use insulation?

It is the practice in some markets to wrap their standard ventilation ducts with a fire insulation.

In other markets, covered by CEN (European Committee for Standardisation), the rules governing ventilation ducts in fire scenarios are covered by product and test standards.  These standards require evidence delivered in tests for the Integrity of the ductwork (E) and Insulation performance when insulated (I).  

You can have an E rating without I, but not an I rating without E.
Insulation is dependant upon the duct maintaining its integrity (E).  

If the duct loses Integrity, the insulation will fail because it will move with the collapsing ducts.  Regular ventilation ducts offer no fire protection, unless they have been designed and tested and classified to have achieved an E rating.  

It’s a system! And it works. 

It delivers the highest possible protection against fire. 

CEN regulation is becoming more widespread and is being adopted as the standard in most European countries, the Middle East, India, the US and Australia. 

All of Thor Duct’s products adhere to the CEN regulation and offer the highest protection against fire and smoke. 

If you have further questions, and you’d like to have a chat with us, contact us or call +353 1 456 8200.

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Q: What should I do with duct that is bigger than 1250mm?

The test standards prescribe the sizes that are tested, and allows for those sizes to be increased to 1250mm X 1000, based on successful tests.  

This can create difficulties.  For example, if you have low ceiling heights, and want a duct to be 1500 X 400, you cannot exceed the 1250 limit on any one side.  The choice is to split the ducts and have two ducts to meet the airflow, e.g., 750 X 500 twice.

Alternatively, duct manufacturers can submit their ducts for testing under EN 15882-1, which allows testing up to 2500 X 1250.  This can be classified under EN 13501-3.  

Lindab Thor Duct ® has a range called Thor Duct ® XL. This fire duct product offers the larger sizes in a single construction with an EI rating.  

Smoke ducts to EN 12101-7 are not yet available above 1250 X 1000, due to prEN 15882-8 not being ready at this time. 

When it is finally published, Lindab Thor Duct ® is ready to test for compliance ensuring that the largest available compliance approved ducts on the market are always available from us.

Q: I’m OK to use BS. Can I still specify BS476 fire ducts?

Yes and No! 

For smoke, no.

For other applications, yes and no. 

It is always EN, but in exceptions BS is often specified.

“Fire safety products must be properly manufactured, tested and certificated in accordance with the latest BS-EN requirements”.

DW144 3rd edition 2016, appendix M (section M.1)

“It is essential that the installed system complies with BS EN1366-1”.

DW172 2nd edition 2018, appendix D (section D6, point 4)

BS9999:2017, states in many examples, notably Fig.31:

“Fire-resisting ductwork classified EISX in accordance with BS EN 13501-3”.

The Building Engineering Services Association (BESA) publication DW172 on kitchens makes the following observation:

“Until such time as BS EN 15871 is published, it is acceptable to use fire resisting ductwork tested to BS476-24. It is for the specifier/designer to decide which product standard to use”.

It is important to note for designers/specifiers that a decision to use what could be a lower standard of fire rated duct places an increased duty on the designer.

Source: Construction (Design and Management) Regulations 2015, Regulation 9, “Duties of designers”. 

This duty requires the designer to reduce or control the risks so that harm is unlikely or the potential consequences less serious. In this context, it requires a demonstration as to why a lower performing duct was selected. 

In Ireland, our duties under BCar are likewise obvious. In Ireland, the standard IS EN 1366-1 was adopted as a national standard in April 2015, and supersedes BS476.

Q: Can I hang other services from my fire ductwork?


Additional services connected to fire ductwork supports may add unknown factors, which in a fire may impact the stability of the ductwork just when it is needed most. Installations need to replicate test scenarios as closely as possible, and additional stresses on support are not accounted for during testing.

Q: Why is my ductwork only E60?

This question arises from classifications carried out under BS EN 13501-3.  

Classifications must be carried out in accordance with clause 7 of EN 13501-3:2005+A1:2009. The standard EN 13501-3:2005+A1:2009 does not provide E classifications higher than the assigned E60.  

I ratings are available for up to 240 minutes. The existence of an I rating greater than 60 is dependant upon the integrity of the ductwork remaining in place during the I rating time frame. The standard however, does not allow for this to be declared past E60.

Q: What must we consider for fire rating of protected stairways, lobbies and corridors?

Historical refurbishment with sate of the art Fire Safety Duct

Have you seen our case study of the work we did on Adare Manor? This is one of the world’s most luxurious hotels, a listed building, and a period building much loved by locals and international guests alike.

In the absence of fire dampers, and where a choice is made to use fire resisting ductwork, fire protection of stairways, lobbies, and corridors in a protected structure should be classified EISX in accordance with BS EN 13501-3, where: 

  • X is the fire resistance in minutes of the walls of the protected route 
  • E represents Integrity 
  • I represents insulation 
  • S is smoke leakage

The ductwork being insulated in this scenario is designed to protect those escaping the scene of the fire, and those who are entering to attack the fire.

If you would like to arrange a CPD with us, call +353 1 456 8200 or get in touch via our contact form and we’ll get right back to you.

MIchael Renaghan

Michael is an expert in fire rated ductwork

For any further questions or to ask about a CPD presentation please contact Michael Renaghan, Technical Lead at Thor Duct ®.