NEW SMOKE VENTILATION REQUIREMENTS: AN OPPORTUNITY TO GAIN BUILDING SPACE

It's not often that new regulations give building engineers, architects, and developers a valuable opportunity to be more creative or make more money, but the latest version of the Approved Document to the Building Regulations Part B - Fire Safety is a welcome exception.

Published in December 2006 and put into effect in April, this latest edition of the Approved Document permits a wider variety of options for smoke control in multi-storey apartment buildings. These increased options can enable space and cost savings in buildings if the right smoke control systems are specified and designed-in.

The Approved Document provides guidance on how to comply with the Building Regulations in England and Wales, and Part B deals with the fire safety aspects of building design. While it provides guidance in a wide range of instances, it should not be considered as a definitive document and alternatives may be considered.

In general, the 2000 Edition of Approved Document B described two applications for ventilating smoke from common corridors, which were:

• Openable Vent (OV), with a minimum free area of 1.0m² for corridors with escape in more than one direction
• Automatic Opening Vent (AOV) with a minimum free area of 1.5m² for a dead end corridor with escape in one direction.

There were several problems associated with these descriptions. For example, there was no definition of "free area", and no suggested alternative if there was no outside wall onto which to locate a ventilator.

Under the December 2006 Edition, the requirement for the application of smoke ventilation in common corridors been changed; a definition of the "free area" has been included; and some alternative solutions are offered.

Smoke Ventilation in Common Corridors

In all instances, a ventilator is required at the top of each stairway equal to 1.0m².

Option A) Small Single Stair Buildings
The requirement for small developments remain the same, with respect to when ventilation should be applied, the only change is how they may be ventilated, which we will discuss in detail further on.

A small single stair building is defined as one where:

• The top floor of the building is no more that 11m above ground level;
• There are no more that three storeys above the ground level storey;
• The stair does not connect to a covered car park;
• The stair does not serve ancillary accommodation (unless separated by a protected lobby, which also needs to be ventilated);
• The stair is ventilated by an openable vent on each level or an openable vent at the head of the stair.

If these criteria are met, the lobby/corridor between the apartments and the stair does not require any form of ventilation if the travel distance is restricted to 4.5m. This distance may be increased to 7.5m if the lobby/corridor is ventilated.

Option B) Other Single Stair Buildings
In other single stair buildings, where the above criteria cannot be met, then the travel distance in one direction is limited to 7.5m. The requirement used to be that the "dead-end" corridor should be ventilated; now the requirement has been simplified so that only the lobby/corridor adjoining the staircase must have smoke ventilation.

In single stair buildings, the ventilation must be controlled automatically, linked to an automatic detection system.

Option C) Buildings with More Than One Escape Stair
Again, where escape is in one direction only, travel distances are limited to 7.5m. Where travel can be to either staircase, i.e. in two directions, travel can be up to 30m before a fire door is required across the corridor.

Again, dead-end sections of corridors used to require automatic ventilation and all other corridors required manual ventilators at the end.

The new requirement is to provide, as with the single stair building, a 1.5m² ventilator in the lobby/corridor adjacent to the staircase, except that in this instance, where the escape is in two directions, the ventilation can be activated manually. This removes the requirement for automatic detection, but the stair vent is required to open at the same time or before the lobby/corridor vent, so some sort of mechanical operation with interlinks is required.

COLT Smoke Ventilation Products

New Definition of Free Area
The new Approved Document now clearly defines the free area of ventilators for all applications as either:

• The aerodynamic free area of the ventilator, as defined by EN 12101 Part 2 and measured by a certified testing body; or
• The total unobstructed cross sectional area, measured in the plane where the area is at a minimum and at right angles to the direction of airflow.

Alternative Solutions
Where before only OV's and AOV's were described, there are now several alternatives available to designers:

• Natural ventilation, using either manual or automatic ventilators (depending on whether it is a single or multi-stair development), located on an outside wall with a minimum free area of 1.5m², as defined above
• Natural ventilation, discharged into a common vertical smoke shaft, closed at the base.
• Mechanical ventilation
• Mechanically, using pressure differentials, in accordance with BS EN 12101-6: 2005.

Natural Shaft Systems
Looking at the new alternatives in a bit more detail, a natural shaft is clearly described as:

• Being closed at the base
• Having a minimum cross-sectional area of 1.5m² with a minimum dimension of 0.85m in either direction
• Extending at least 0.5m above the highest structure within 2m
• Extending 2.5m above the ceiling of the highest level served by the shaft

The vent into the shaft, the vent at the top of the shaft and any safety grilles in the shaft should all have a minimum free area of 1.0m².

The shaft should be constructed from non-combustible material and the vents should be equivalent to a E30Sa fire door. The shaft should be vertical with no more than 4m at an inclined angle (maximum 300).

On detection of smoke in the corridor, the vent on the fire floor, at the top of the shaft, and the top of the stair, should all open simultaneously. Vents on all other levels should remain closed.

Colt offers two alternatives for the device between the shaft and the lobby/corridor. The first is a damper, with a decorative grille (see Defender); the alternative is a door mechanism, which operates a standard fire door (see Doorman).

Mechanical Ventilation
Approved Document B permits the use of mechanical ventilation for smoke control of common escape routes but gives no design guidance on how to design such a system.

Based on Colt's experience from developing other mechanical shaft solutions, such as the Colt Shaft fan-powered system for fire fighting applications, several options are available to reduce the natural shaft from 1.5m². In its first installation last year, in the seven-storey Hoxton Hotel in London, the Colt Shaft was half the cost of the system previously favoured by the developer and required a shaft of only 0.6m² compared with 3m² for a conventional BRE shaft. This represented an 80 percent reduction in the floor space required, giving the hotel more revenue-earning space.

However, unlike the fire fighting application, means-of-escape mechanical solutions require dedicated inlet air or supply air systems. This permits full extract to take place without creating large negative pressures or compromising fire compartmentation. The innovative new Colt Extended Corridor Solution (corridor ventilation) achieves better smoke extraction than conventional AOV corridors, also offering developers substantial space and cost savings.

The Extended Corridor achieves exceptional smoke extraction performance by utilising a corridor extraction system at one end of the corridor and a dedicated air inlet system at the other. Inlet air prevents the corridor from becoming excessively depressurised, as depressurised air could make it difficult for evacuees and fire fighters to open doors and could cause extract fans to stall with resulting failure of the total system.

With local authority approval, the first Extended Corridor is currently being installed in a residential building at the Angel Meadows development in Manchester, where it has extended the escape distance in the corridor from 7.5m to 18.0m in one direction, making it possible to omit one staircase. This has gained useable space and saved building costs. (see press release)

Space-gaining solutions
The key message here is that the recommendations in Approved Document B are by no means exhaustive, and it pays to consider alternative smoke control systems in multi-storey buildings. By allowing a wider variety of options for smoke control in apartment buildings, the 2006 edition of ADB gives building engineers and developers a valuable opportunity to save costs and gain saleable floor space. Seize the opportunity!

Pressurisation Systems
Pressurisation systems protect escape routes and fire-fighting shafts against the ingress of smoke by maintaining a higher pressure within the escape route than in the adjacent spaces.

A pressurisation system consists of three main components: Supply Air (where air is injected into the area that is to be protected), Pressure Relief (to avoid overpressure when doors are closed), and Air Release (air and smoke is released from the adjoining fire area). Combining these elements creates a positive pressure difference which prevents lobbies and staircases from filling up with smoke.

Pressurisation systems should meet the recommendations of Approved Document B and BS EN 12101-6: 2005 Specification for Pressure Differential Systems - Kits.

Pressurisation systems are the most effective at keeping smoke free conditions in staircases and corridors, but also the most complex to design and install. Providing an air release path can be extremely difficult, particularly in apartment buildings where the only path to outside is often through the apartments themselves. In most instances, this proves impractical. For more information on Pressurisation Systems, click here.