Sealing around fire-rated ductwork requires early collaboration between key stakeholders to make sure the correct firestopping system is selected. Because the service penetration sealing method depends on the ductwork manufacturer’s test evidence, it’s important to review that evidence (and installation guidance!) before specifying any products.
What is fire-rated ductwork?
Purpose of fire-rated ductwork in buildings
Unlike standard metal ductwork, the fire-rated type is designed to maintain building compartmentation and prevent the spread of fire and smoke through ventilation for a specified time.
This type of ductwork is typically found in fire-resisting walls, floors, shafts, or protected escape routes, and is often referred to as a fire duct or a fire-resisting duct system.
Fire ducts can be formed from a variety of systems, such as thicker specialised sheet material, fire protection coatings, or wrapped in high-performing fire protection materials.
Why do openings around ductwork create fire compartmentation risks?
Fire always follows the path of least resistance. Even a small break in the compartmentation line will allow it to pass into the adjacent partition and cause extensive damage. Therefore, it is crucial to correctly seal all service penetrations, not just ductwork, to prevent the spread of fire.
Role in maintaining compartmentation
As a critical element of passive fire protection, fire compartmentation depends on early stakeholder engagement, typically at RIBA Stages 2/3, to prioritise fire safety from the very start of the project.
It involves dividing the premises into areas of controlled risk using fire-resistant walls and floors, and sealing any breakage in the compartment line using the correct, tested fire stopping products to contain the fire to its area of origin.
When compliant compartmentation is achieved, in the event of a fire, it protects those residing in the building by providing time for the fire service to arrive at the scene, get the fire under control, and rescue those who may still be in the building.
Key standards and installation considerations
What test standards are used for fire-rated ductwork?
The primary standard for fire resistance testing of ductwork in Europe and the UK is BS EN 1366-1.
It also provides the foundation for smoke extract ducts, which require a 90% free area. This means at least 90% of the opening must remain clear to allow airflow and smoke extraction.
Other standards for ductwork exist in the BS EN 1366 series, such as:
- BS EN 1366-5: Specifies a method for determining the fire resistance of horizontal service ducts and vertical service shafts.
- BS EN 1366-8: Fire-resistance tests for smoke extraction ducts that have already passed the appropriate test to BS EN 1366-1.
- BS EN 1366-9: Fire-resistance tests for smoke extraction ducts used only in single-compartment applications, i.e., ducts that remain within the compartment of fire origin and exhaust to the exterior of the building without passing through another fire compartment.
What classification standards are used for fire-rated ductwork?
Unlike our product applications, which are tested to BS EN 1366-3 or BS EN 1366-4 and then classified under BS EN 13501-2, ventilation and kitchen extract ducts are classified to BS EN 13501-2. Meanwhile, smoke extract ducts are classified to BS EN 13501-4.
The fire-resistance information is also available in a different format, such as the following:
|
E |
I |
120 |
( |
i |
< |
o |
) |
Ho |
Ve |
S |
|
Integrity |
Insulation |
Time in |
|
Tested for fire inside the duct |
|
Tested for fire outside the duct |
|
Tested for |
Tested for |
Tested for |
For example, a classification rating of EI 120 (VeHo i<>o) indicates that a ventilation duct is capable of reaching 120 minutes of integrity and insulation in both directions (inside to outside and vice versa) in vertical and horizontal applications.
Adding 'S' signifies a leakage rate below 5m³ per m² per hour. The pressures 500Pa, 1000Pa, or 1500Pa show the negative pressures the duct can handle, and they also indicate it can withstand a positive pressure up to 500Pa.
What spacing is required around fire-rated ductwork penetrations?
If spacing isn’t properly considered at the design stage, it can lead to major problems later in the project. That’s why we always advise you to speak directly with the fire duct manufacturer about the requirements for their system and how those requirements relate to the fire test evidence.
Unfortunately, from our side, all we can advise is that the fire duct must not share an aperture with other services, such as cables or pipework. This is because these systems are tested to their own fire-resistance standards rather than to BS EN 1366-3.
The distance between apertures in supporting constructions should be at least 200mm to comply with Section 13.7 of BS EN 1366-3:
However, the flexible wall manufacturer or the structural engineer for rigid walls and floors may require a greater distance between apertures, and the larger requirement must be followed.
So, when would Quelfire’s product be used around fire-rated ductwork?
This would depend solely on the ductwork system’s test evidence and requirements. We haven’t tested any specific ductwork system and are therefore unable to comment on such applications.
Some fire duct manufacturers may have tested certain applications with their systems, where additional products, such as fire batt or mortar/compound, can be used.
They will then either specify which fire batt or mortar/compound products can be used, or state certain material specification requirements.
So, for example, when it comes to fire batt, you may see the following minimum material specifications:
- Fire batt with a minimum rock fibre density of 140kg/m³: QuelStop Fire Batt is 140kg/m³ density.
- Fire batt with a minimum ‘Reaction to Fire’ rating of Class E: QuelStop Fire Batt is rated Class E.
For acrylic sealant, you may find the following:
-
Acrylic sealant that is tested to BS EN 1366-4: QuelStop Intumescent Acrylic Sealant is tested to both BS EN 1366-4 and BS EN 1366-3.
For mortar/compound:
- Fire protection mortar tested to EN 998-2, Classes M2.5 – M20: QF2 Fire Protection Compound has been tested to EN 998-2. EN 998-2 no longer shows M ratings on certificates. However, if it were still shown, our QF2 compound would be rated M5 due to its compressive strength, as shown in this table:
Why test evidence is essential for compliance
Importance of tested system evidence
The only true way to guarantee the effective compartmentation of a building is to use passive fire protection systems that have been tested in a fire scenario.
Without reliable test evidence of the system’s performance, there is no way to confirm that the installed materials will perform as intended for the required period.
It also provides confidence that the systems used are compatible and compliant with building regulations!
Early engagement in firestopping
The foundation of any successful project is early engagement. By this, we mean bringing together all parties involved in the design and installation of fire stop systems to discuss project objectives and ultimately ensure that firestopping remains a top priority.
Installations can be carried out without regard for the next trade, inevitably leading to a domino effect of costly and time-consuming errors.
But this can be avoided by engaging early and ensuring that spacing, installation, and maintenance are considered to prevent issues later in the programme.
Ultimately, early engagement guarantees that the building is designed, then built around the available firestopping solutions to protect people and property, and improve communication between key teams.
Frequently asked questions on fire-rated ductwork
What is the difference between a fire-rated duct and a normal duct?
Simply, a fire duct is designed to withstand the high temperatures of a fire. Compared to standard ducting, it will maintain its structure and function for the amount of time it was successfully fire tested. Normal ductwork moves air, not resists fire!
Who is responsible for ensuring ductwork penetrations are compliant?
The topic of responsibility has always sparked debate within the construction industry, but the simple answer is that those with any level of involvement in the specification, design, and installation all carry responsibility. So, this would be between designers, installers, manufacturers, and also those signing off on the installations.
If you have any further questions, please don’t hesitate to contact us. We’re here to help!
