INTRODUCTION

The objective of this publication is to provide technical data and guidance for defining a robust, appropriate and acceptable design fire for the fire safety engineering design of a building. It explains:

• what a design fire is
• how it can be determined
• its limitations
• the experimental data (where available)
• current calculation methods used for defining a design fire.

Depending on the geographical location of a building, its legislative fire safety requirements may be achieved in a number of ways. Fire safety engineering is a generally accepted approach for demonstrating that the legislative fire safety requirements of a design have been achieved.

A building design which is supported by a performance-based fire safety engineered solution comprises a number of components. One of these critical components is the selection of an appropriate and relevant design fire. In a performance-based fire safety engineered solution the design fire will determine a number of important parameters for a given space, which include:

• the quantity of heat released
• the quantity of smoke produced
• the composition of the smoke
• the fire size
• the temperature of a smoke layer
• the time to involvement of all exposed combustible materials
• the fire duration.

Based on the values determined for the parameters, a fire engineered analysis can establish:

• if predetermined tenability criteria are exceeded
• if further fire protection measures are required (eg a smoke control system)
• the specification of such fire protection measures.

Clearly, there is great significance associated with the selection by the fire safety engineer of an appropriate design fire to ensure it is representative of the situation considered to fulfil the life safety requirements. In addition to this, it is important to determine if the fire safety measures proposed by a fire safety engineered solution are proportionate (ie not overly onerous, resulting in unnecessary expenditure), but nevertheless capable of meeting the life safety requirements to avoid potentially life-threatening omissions.

There are a number of different approaches to defining an appropriate design fire ranging from calculation based on fuel load surveys of real buildings and quantification to experimental determination. These different approaches will be described in detail.

This publication is aimed at those professionals involved in the fire safety engineering design process, either as a designer fulfilling a brief or a regulator/ approver of the design. It is intended that this publication will provide evidence to assist the review of the foundation of the fire engineered solution as part of any approval process.

More generally, those in the position of the responsible person, as defined by the Regulatory Reform (Fire Safety Order) 2005^[1] (FSO), or those delegated as competent under the FSO by the responsible person, are likely to find this resource beneficial when undertaking a fire safety risk assessment in both fire safety engineered and non-fire safety engineered buildings. That is, it is important that the responsible person understands the design principles of his or her buildings so that he or she can ensure that they are managed on an ongoing basis, within their design limits. Specifically, the fire load is restricted to within the limits of the assumed design fire. This is particularly important where, for example, a change of use or change of ownership might occur.

Fire safety engineering design requires the identification of an appropriate fire size on which a design can be based^[2,3]. This is one of the key decisions in fire safety engineering design and requires formulation of a quantitative description of the fire. Published reliable data is scarce and fire safety engineers often resort to a simple generic description based on assumption.

A summary of the most commonly used parameters in fire safety engineering are detailed as part of the summary of each of the experimental fires where available and include the following parameters:

• HRR
• heat of combustion
• mass of fire load
• optical density
• carbon dioxide concentration
• carbon monoxide concentration.