Lawrence Webster Forrest
Tel: +44 (0)20 8668 8663 Fax: +44 (0)20 8668 8583
Lawrence Webster Forrest
Tel: +44 (0)20 8668 8663 Fax: +44 (0)20 8668 8583
An important part of a building's infrastructure is the ducting network that runs throughout the premises, it is often invisible, but is a key element to the environmental operations in a building. Ducting may carry fresh air to improve the environmental ambience for the occupants in the building, or may serve a dirtier role in helping to remove smells, dust or toxic gases from a room or piece of equipment. It may also form part of the vital systems to protect occupants from the effects of smoke, or help prevent fire spread. Whatever its role, most ductwork must travel extended distances through a building to reach its destination – usually the open air or treatment plant.
What’s so important about ductwork?
Not much notice is taken of the ductwork in a building – indeed it and its associated dampers are often neglected and forgotten. We can never underestimate the importance of these systems, both in keeping us comfortable, or as far as risking our lives or the integrity of the building to which it is installed.
Buildings are designed with fire resistant enclosures, known as compartments, to contain any fire within one area. Due to its possible routes through a building, ductwork is a key element that can, if not suitably protected, weaken the passive fire protection built into a building through the construction of fire walls and floors / ceilings. Without adequate fire resistance, along with the other services installed such as plumbing, electrical wiring or communication cabling, this can lead to rapid uncontrolled spread of smoke and fire through an entire building, often without the occupants being aware for some time.
Why make ductwork fire resistant?
Fire resistant ductwork and dampers can prevent fire spread from the room of origin, thus protecting occupants, and the fabric of the building.
While specially made fire resistant ductwork can be acquired, there are also different methods of protecting ductwork. It can be enclosed within a fire resisting material, commonly plasterboard or other substance designed specifically for this purpose. Dampers can be fitted within the compartment wall to seal the building structure in the event of a fire.
In the same way that fire doors are provided within compartment walls, dampers are also provided within compartment walls and floors where ducting passes. These allow free access throughout the ducting system normally, but will shut down and prevent the passage of smoke and flames between compartments in the event of a fire. Dampers can be linked to the fire alarm and close when this is triggered, or thermal links may activate when exposed to high temperatures . These are typically set to activate at temperatures of 72°C ± 4°C.
As with fire doors, ductwork and damper fire resistance must match the fire rating of the compartment through which they pass or are installed in.
There may be many reasons why fire resisting ductwork and dampers are installed, for example:
1. To be used for smoke extract in the case of a fire in fire engineered solutions.
This may be the case in basements, car parks or means of escape, to increase the available safe egress time for occupants by helping prevent the build up of toxic gases and heat. The ducting is responsible for removing smoke from an area, which can reach high temperatures very quickly. The system, including any fans, must also be able to withstand these high temperatures long enough that all occupants can safely evacuate.
Where smoke extract is required in basement areas, these areas must also be provided with sprinklers. The ductwork in this case must be able to prevent water ingress as well as high temperatures, and also the possibility of thermal shock from sprinkler systems activating.
2. Kitchen extract systems (non domestic).
These systems are a particular risk, especially if the required maintenance and cleaning regimes are not adhered to. The build up of grease and fat within the ducting, coupled with high temperatures, can self ignite and cause a fire in the ducting itself. It is important that this fire does not break out of the ducting into adjacent rooms or service risers, and that radiant heat is minimised to prevent ignition of a second fire outside the duct.
It must be noted that dampers must not be installed to kitchen extract systems, so further emphasis on the fire resistance of the ducting is made.
3. The ductwork passes through a means of escape.
Where the ductwork must pass through a means of escape, then it must be capable of protecting that escape route from a fire in the adjacent rooms to which it is linked, much like the fire doors to which we are accustomed.
What makes ductwork fire resistant?
Ductwork must pass three key tests before it can conform to British Standards:
Tests are performed on the ducting as a whole, including joints and hangers, so you can be assured that the whole system will perform as required in the event of a fire.
In order to achieve adequate fire resistance, ducting can be treated in various ways. The ducting can be coated, sprayed, enclosed or wrapped in a wide range of proprietary materials available from a large number of manufacturers. As with maintenance of the ductwork itself, the protection supplied must also be maintained and protected from damage when works are carried out.
As can be seen from this bulletin, fire resistant ductwork and dampers can be key to preventing unforeseen fire spread throughout your building. It is therefore imperative that if any works are being undertaken to ductwork within your property that you clearly understand any fire rating or resistance that maybe necessary to that ductwork.
This bulletin has been written by Karissa Thomas DipHE Fire Safety.
In LWF’s fire engineering blog series for Architects and other professionals involved in building design, we have been looking at firefighting and, most recently, the provisions that should be made for the Fire Service to attend and put out a fire. In part 23, we looked at the requirements and recommendations relating to the provision of fire hydrants and we continue from that point in part 24.The original standards for the installation of water...
In LWFs blog series for healthcare professionals, the aim is to give information on best practice of fire safety in hospitals and other healthcare premises. In part 57 of this series, LWF looked at what access and facilities must be provided for the Fire Service attending a fire at a healthcare venue. In part 58, we will continue from that point by looking at the number and location of fire-fighting shafts required in those healthcare...
In LWF’s blog series for those professionals who work in facilities management or who have an interest in or responsibility for fire safety, we have been looking at property protection and the role of the insurer. In part 4, some of the history that led to property insurance from fire was given and in part 5, we will continue looking at how different the early insurers could be from what we know today.While the...
In LWFs fire engineering blog series for Architects and others involved in building design, we have been looking at the subject of firefighting. In part 22, we gave information on some of the regulations and guidance documents which deal with the issue of provision of fire hydrants. In part 23, we continue from that point by looking at who should provide them and where they should be placed in relation to the building.
In LWFs blog series for healthcare professionals, the aim is to give information on best practice of fire safety in hospitals and other healthcare premises. In part 56 of this series, LWF spent time looking at the access required by Fire and Rescue Service vehicles to healthcare buildings not fitted with fire mains. In part 57, LWF will continue looking at those measures which should be taken to ensure the Fire Service has access to...
The Wohl Neuroscience Institute - Fire Safety, Strategy & Engineering
Key Facts: Client: King’s Clinical Neuroscience Institute Project Manager: MACE Ltd Designers: Devereux Architects/Allies and Morrison Approximate Size: 7,400m2 Description of the Project:...
Fire - The External Risk
When we consider fire safety, our focus is normally from within, what can we do to prevent the occurrence of fire and how we can limit its damage.Â Whilst this is the correct stance to take, we m...
Evacuation Modelling - Factor in Human Behaviour
Evacuation of buildings can be analyzed in different ways. Approved Document B (ADB) which provides guidance on meeting the requirements of the England and Wales Building Regulations with regard to fi...