BRE BR187 PDF

Introduction

Most accidental fires start as small fires which initially present a very small hazard to adjacent buildings. However, as a fire grows, windows in the burning building will break and other openings in the external envelope may develop; this provides the potential for fire to spread to adjacent buildings by contact with flames and hot gases from the openings, thermal radiation or by burning brands (burning debris from the fire) drifting in the wind.

Buildings are not normally close enough together for fire to spread by direct contact from flames, although a fire could propagate across combustible materials between buildings such as stored materials, wooden sheds, fences, garden debris, rubbish and even cars or caravans parked between buildings. These factors are beyond the scope of building separation and boundary distances and are more relevant to the use of the building which, in England and Wales, is controlled by the Regulatory Reform (Fire Safety) Order 2005^[16] and in Scotland under Part 3 of the Fire Safety (Scotland) Amendment Regulations 2006, as amended in 2010^[17].

The presence of fire brands from a burning building will be dependent on the materials that are burning. They are, by their nature, small and have the potential to travel a significant distance, maybe several hundred metres. This is an important mechanism of fire spread in wildfires and needs to be considered when, for example selecting roof materials for a building located in woodland. Burning debris from a fire at high level in a tall building also has the potential to spread fire to lower parts of the building if the material falls onto balconies or is blown into a room through open windows. Burning debris may also ignite items such as vehicles at ground level. The main concern here is that a brand could provide a pilot ignition source for materials on an adjacent building that has been heated by thermal radiation from the fire.

If a fire is allowed to develop, as windows in the compartment break, more air can enter the compartment allowing the fire to grow until it is limited either by the amount of fuel, availability of air or the extent of the compartment. Thermal radiation from the external openings in the burning compartment, and from flames leaving the compartment, will then heat surfaces on adjacent buildings. This has the potential, especially if burning brands are present, to ignite the surface(s) of an adjacent building. If left unchecked the fire could then propagate from building to building and develop into a large urban fire. These have occurred many times in history either as the result of accidental fires, for example in London, UK in 1666[9], Oaklands, USA, 1993^[18], during warfare in German and Japanese cities during WWII^[19] or as a consequence of natural disasters such as volcanoes in Montserrat, The Caribbean, 1997^[20], and earthquakes in Kobe, Japan, 1995^[21].

It has been known for a long time that fire spread due to thermal radiation can be controlled by adjusting the size of buildings and openings, and the distance between buildings. For example, the Building Act of 1667^[22] following the Great Fire of London had requirements relating the height of buildings to the width of streets and for the use of non-combustible materials. The scientific basis of this approach was explored through the 1950s following post-war building studies and resulted in calculation methods which were first made a requirement in the Building Standards (Scotland) Regulations 1963^[10] and was shortly followed by similar requirements being introduced in legislation for England and Wales^[11]. Technical paper 5 Heat radiation from fires and building separation[2] summarised the background to these calculations.

This guide will allow the reader to trace the development of boundary distance requirements in the building regulations since World War II which is of practical relevance today. Existing buildings will have been built to the building regulations and requirements of the time of their construction. The redevelopment of a site or refurbishment of an existing building will need to consider, and may be constrained, by the location of previous and surrounding buildings.