EVEN IN today's difficult economic climate, many affluent cities around the world have witnessed an increased demand for luxury apartments. This can be seen in the UK - in particular, London - with recent constructions such as the 'One Hyde Park' development. Located in the heart of Knightsbridge, it contains a number of large open-plan apartments. It is one of the latest examples of these luxurious modern residential developments.

Even away from the high-end market, open-plan apartments are increasing in popularity as more and more people choose flats over houses, owing to affordability and the desire for a sense of interior space. The Strata Tower - part of the redevelopment of Elephant and Castle in London - contains 418 flats, all of which are open plan.

The fire safety design of residential buildings already brings with it a number of interesting and unique challenges, such as the maintenance of fire safety systems, the lack of control of the furnishings and storage in apartments, and the stay-in place evacuation strategy. It also covers a very wide range of apartment types, ranging from luxury apartments, to simple bedsit-type apartments.

With the increased demand now being seen, many developers are asking architects to produce more innovative designs that push the limits of guidance given by the Building Regulations in England and Wales, specially in terms of the restrictive fire safety guidance contained within Approved Document B (ADB) and BS 5588-1: Fire precautions in the design, construction and use of buildings. Code of practice for residential buildings.

This, added to the fact that there have been a number of high-profile fires in residential towers, has focused attention on the fire safety design of residential buildings.

Restrictive guidance

 The types of esigns that are common with these residential developments often contain the following features:

• open-plan apartments with extended travel distances
• duplex (two-floor) apartments
• inner rooms

These types of designs are not compliant with the guidance in ADB for the internal layouts of apartments. ADB referred to a series of British Standards, BS 5588, that have recently been superseded by BS 9999: Code of practice for fire safety in the design, management and use of buildings, which allows for a more risk-based approach to design, and gives approval authorities more guidance on compensation measures, such as the introduction of sprinkler systems. However, the guidance for residential buildings in BS 5588-1 was not superseded.

The guidance given is very restrictive and allows for the following design approaches:

• limiting the travel distance from any point in the apartment to the entrance door to 9m, and locating cooking facilities remote from the door; or
• providing a protected entrance hall serving all habitable rooms, with a maximum travel distance from the door of any room to the entrance door of the flat of 9m; or
• providing an alternative exit or exits from the flat

This guidance achieves the life safety requirements set out in the Building Regulations by:

• keeping travel distances to a minimum, to allow occupants to escape from the apartment before conditions become untenable
• using compartmentation to protect escape routes
• allowing the occupants to move away from the fire when they escape

There are issues with these approaches, namely:

• the first approach, of restricting the travel distance in the flat, does not allow for the design of luxury open-plan apartments, and therefore omits these designs from being acceptable under the Building Regulations
• the approach of using compartmentation by a protected entrance hall has been negated by the fact that ADB no longer recommends internal fire-resisting doors to have self-closers. Therefore, we must assume that these doors will be open
• providing an alternative exit would require an extra stair core in the building for floors above ground

The restrictive nature of the guidance in ADB can be seen by comparing it to the US National Fire Protection Association Life Safety Code, NFPA 101. The NFPA design allows for a 23m travel distance in an apartment that is not sprinkler protected, and a 38m travel distance in a sprinkler protected apartment.

As BS 5588-1 does not include flexibility in design for compensatory measures such as fire suppression, fire engineered solutions are therefore commonplace in fire strategies for luxury apartments. Recently, the National House-Building Council (NHBC) Foundation published a research report, Open-plan flat layouts - Assessing life safety in the event of fire, to help ensure a more coherent approach and highlight unacceptable risks. This concludes that travel distances in apartments are not a significant factor in the life safety of occupants.

However, the research focuses on smaller open-plan apartments (12m x 16m), and does not investigate the larger apartments or duplex apartments that are becoming more commonplace.

Engineered solutions
There are a number of fire engineered solutions that are used to justify the designs that are found in luxury apartments, each with their advantages and disadvantages. 

Fire suppression:

The use of fire suppression to limit fire growth and spread in apartments, and therefore maintain tenability for means of escape, is often used to justify extended travel distances and reduced fire separation in apartment layouts.

As stated earlier, the use of sprinkler protection is recognised in other countries around the world as a compensatory feature to allow flexibility in residential design, and is also used in the UK to decrease risk levels for other building types in the guidance laid out in BS 9999. A BRE research report on the effectiveness of sprinklers in residential premises shows Open-plan and duplex apartments are increasingly common in modern residential developments, but are not compliant with ADB guidance that sprinklers maintained tenable conditions in terms of toxicity and reduced the effects of convection, but produced no observed improvement in visibility. Common concerns relate to the maintenance of systems, with problems such as residents refurbishing apartments, and covering or painting over sprinkler heads.

Smoke extract:

Smoke extract from apartments is less commonplace in fire engineered solutions for apartments. It can be used in large apartments to maintain a clear layer height so that occupants can escape in tenable conditions; or used to prevent smoke from spilling out of a reservoir around an area of high risk that is created with downstands.

Apartment layouts:

An approach often used to increase the level of life safety in an apartment without the installation of life safety systems is the use of the apartment layout itself. An example of this is the upside-down approach often used for duplex apartments, where the designer will place all areas of fire risk on the upper level of the apartment and the sleeping risk on the lower access level of the apartment.

Fire curtains:

Fire curtains are a way of providing a form of fire separation to an apartment without affecting the day-to-day layout. Life safety requirements can be achieved by using fire curtains to enclose areas of risk and by protecting escape routes. Again, there are concerns that items of furnishing, for example, could be placed under curtains, preventing them from lowering properly and therefore rendering them useless.

Consistent approach 

Although there are many fire engineered solutions for residential design, a lack of flexibility in design guidance in the UK appears to result from a lack of published quantitative data and guidance on the subject. The NHBC Foundation report on open-plan flat design is one of the first in the UK.

As demand to push the boundaries of residential design intensifies, there is a need to help approval authorities and fire engineers produce a consistent approach. It is also evident that, if life safety systems are to be introduced to allow flexibility in design, issues such as maintenance and flexibility need to be resolved. From discussion with approval authorities, it is evident that they have concerns over the use of complex systems, such as smoke extract or fire curtains, due to the issue of maintenance and ownership of the systems, as well as the effect of alterations in the apartment by the owner adversely affecting system performance.

With many more of us seeking to take advantage of open plan living, much work still needs to be done to produce a quantitative and consistent approach to fire safety design for probably the most important building type ñ the home

Stewart Dabin BEng(Hons), AIFireE is a
fire safety engineer with Kingfell Consulting

The NHBC report, 'Open-plan flat layouts - Assessing life safety in the event of fire', is available from the 'Research and publications' section of www.nhbcfoundation.org

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