5.2.1 Introduction

Fires in process plants can take many forms:

• pool fires,

• jet fires,

• fireballs, and

• flash fires.

The damage done by such fires depends on several effects:

• flame impingement,

• convection, and

• heat radiation.

Fireballs are described in Section 5.3. Flash fires are described in Section 5.4.

5.2.2 Pool Fires

A pool fire is the combustion of material evaporating from a layer of liquid at the base of a fire. It typically occurs when a pool of spilled flammable or combustible liquid is ignited.

The behavior of the resulting fire depends on a number of factors. These include:

• the nature of the liquid being burned,

• the ambient temperature,

• the effective diameter of the pool, and

• the extent of any breeze.

These affect the rate of vapor formation to provide fuel, and the supply of oxygen to the fire. The more volatile the liquid and the greater the ambient temperature (especially of the ground), the greater the rate of fuel supply. The greater the diameter of the pool, the less efficient is the supply of oxygen to the flame, resulting in a less radiant and more smoky flame. The greater the breeze, the greater the supply of oxygen, and the brighter and more radiant the flame.

In assessing the effects of a postulated fire, a number of assumptions are often made, relating to:

• the height of the flame above the pool,

• the inclination of the flame in the event of a breeze,

• the rate at which the pool burns...