The LWF Blog

Thinking outside the box – Part two – Internal planning of flats – fire engineering solutions

July 8, 2013 10:17 am

In part one of this series, we looked at how the demand for increasingly innovative builds has led to a need for more inventive fire engineering solutions for escape stairs and common corridors. In this second part, we will continue the theme of thinking about solutions to fire safety that lie outside the traditional building standards and codes of practice, to enable creative design for the internal planning of flats.

Internal Planning of Flats

A common complaint of prescriptive internal flat layouts is that they are monotonous and dull due to inflexible standards.  

An example of this is that if the design of the flats meets the prescriptive guidance, such as BS 9991 or Approved Document B, they would meet current building regulations. 

In studio flats, this is likely to lead to a layout with the kitchen positioned remotely from the entrance door and the travel distance limited to 9m internally, from the furthest point to the entrance door to the flat. An entrance hall is a necessity for flats with one bedroom or more, with the travel distance of 9m internally applying, as for studio flats.

Some desirable features of flat design, (that are likely to put a spoke in the wheel of the fire safety requirements), include inner rooms, open plan layouts with extended travel distances and duplex flat layouts. 
A fire engineered approach to fire safety when designing and building can help to make more imaginative design a possibility.
In designs where the bedrooms are inner rooms, for example (i.e. not reached directly from the inner hallway) fire engineers could recommend the following measures to compensate:

• Early warning of a fire
• Automatic suppression systems
• Smoke control systems

As a minimum provision for existing domestic premises, a category LD3 detection system (in accordance with BS 5839: Part 6) is used in the flat entrance hall only. However BS5839: Part 6 comments that for new premises and always in sheltered housing a category LD2 system is more appropriate. While the installation of a category LD1 coverage system might be considered in excess of the code compliance, the inclusion of smoke detectors in the bedrooms, living room and a heat detector near to the cooking space can avoid a situation where smoke from a fire in the kitchen area has to leak through to the hallway, and that the hallway alarm has to wake those sleeping in one of the bedrooms.

Research on life safety of open plan flats in the event of fire undertaken by the National House Building Council (NHBC) Foundation, concluded that although a significant benefit can be seen, there is concern that enhanced detection alone cannot satisfy the requirements of the Building Regulations. 

Automatic suppression systems

It is recognised that the activation of an automatic suppression system has the effect of reducing the toxicity and temperature levels within a flat. The validity of an automatic suppression system as a fire safety solution for flats is not conclusive.While the automatic suppression system is considered as a compensatory measure in Approved Document B, research on the effectiveness of residential sprinklers was undertaken by the Building Research Establishment (BRE) and observations of the visibility level indicated that there was no improvement with sprinkler coverage.  This means that, on occasion, approving authorities raise concerns relating to the conditions of visibility and request further justifications. 

However, research undertaken by NHBC has demonstrated that open plan flat layouts with an automatic suppression system in accordance with BS 9251 and a Category LD1 detection system provides a level of safety equivalent to or better than the minimum recommended provision in the Approved Document B (note: research was based on flat layouts with a maximum size of 12m x 16m and larger layouts would require further analysis). 

Active fire safety systems

Other active fire engineering systems such as smoke curtains, mechanical or natural smoke control systems are common practice in large assembly and public buildings e.g. shopping centres, atrium and office buildings. Where used these systems could potentially maintain clear layer heights, limit temperatures and keep escape routes clear.

With respect to internal planning of flats the application of active fire engineering systems are rare but there is scope for this type of system in unconventional dwellings where protected routes are compromised by an open plan layout.

The application of active fire safety systems can be very effective, however, some approving authorities may have concerns with regards to the ongoing maintenance of these systems and some assurance of how this will be achieved is often required