The tunnel test results should therefore be used with considerable caution in predicting the ignition behaviour of materials. Consider, for example, how to rate a large wall hanging of textile fabric. A large flame is applied and the time taken for it to pass down the tunnel is measured. The conditions of burning are most unlike those to he expected of a textile hanging on a wall and probably represent a far less severe condition than the most likely fire scenario. Often it is not possible to identify all the factors involved in practical ignitions.
Regulators rely mainly on the results of test procedures that simulate the actual application.
These demonstrations, however, can be far more expensive than the more controlled, laboratory test procedures and they are often less informative. Fire behaviour is influenced by so many uncontrolled variables that prediction is extremely difficult. A useful technique is the worst case scenario. As serious a set of circumstances as can be envisaged is selected and material performance is assessed under those conditions. If the result is satisfactory, there is a high probability that the material will perform well in less severe fire conditions.