Fire Rated DuctWork

Ductwork, ducts are pipes that typically form part of a ventilation system, used to carry air throughout a building. For example, the simple elementary duct is a fireplace chimney, used to convey smoke to the outside.

Importance Of Ductwork?

Although not much signs is taken of the ductwork in a building, we can never underestimate the importance of this system in keeping us comfortable.

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 protect and weaken the passive fire protection built into a building through the construction of fire walls, floors and 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 aware during the early period.

Types Of Fire Resistant Ductwork

There are four basic types of fire-resistant ductwork that could be required and have special use under fire conditions. The following terms are used in identifying varying performance criteria for such ducts.

1. Ventilation fire ductwork: This ductwork is fire rated where it passes through a fire compartment. For example, an escape corridor. An escape corridor should always be tested for type A fire outside and type B fire inside criteria. However, it is not necessary for the ductwork to maintain its cross-sectional area in a fire.
2. Smoke extract fire ductwork: This ductwork is for extracting smoke from the building and should be fire rated equal to the compartment walls or floors through which is passes for stability, integrity and insulation. The duct must also be tested to prove its cross-sectional area does not reduce by more than 25%, both inside and outside the furnace, and to ensure that it will achieve its primary function, of extracting smoke.
3. Non-domestic kitchen extract fire ductwork: This is occasionally called grease ducting and should be tested for both type A fire outside and type B fire inside. Both tests are required as it is important to prevent flammable grease from either catching fire when it passes through an adjacent area, or if the grease itself is already alight, causing a fire to start within the adjacent area by radiant heat. Fire dampers should not be used in kitchen extract ductwork.
4. Pressurisation ductwork: This is a method of restricting the penetration of smoke into certain critical areas of the building by ensuring the air within those areas is at a higher pressure than in adjacent areas. These areas apply to protected stairways, lobbies and corridors as smoke inhibits escape.

What Makes Ductwork Fire Resistant?

Ductwork must pass these three key tests below before it can get to a British Standards:

• Stability – the ability to resist collapse when exposed to fire conditions
• Integrity – the ability to resist penetration from flames, and smoke etc
• Insulation – the ability to prevent radiative spread of fire

When tests are performed, it is done on the ducting, including joints and hangers. This can guarantee you that the whole system will perform as required in the event of a fire.

Ducting can be treated in various ways to achieve adequate fire resistance. The ducting can be coated, sprayed, enclosed or wrapped in a wide range of proprietary materials available from many manufacturers. However, with maintenance of the ductwork itself, the protection supplied must also be maintained and protected from damage when works are carried out.

From ductwork fire resistant, dampers can be key to preventing unexpected fire spread throughout the building. It is recommended that if any works are being undertaken to ductwork within your property, that you clearly understand any fire rating or resistance that is necessary to that ductwork.