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Figure 59. The fi re has<br />
spread to other objects<br />
in the room. Soon the<br />
whole room will be<br />
involved.<br />
86<br />
es in the smoke gas layer and the radiation to the lower parts<br />
of the room will then start to increase. This process will then<br />
be able to accelerate, leading to what is known as a fl ashover.<br />
Flashovers in buildings sometimes result in people dying,<br />
which is why it is important to be familiar with the situations<br />
which cause fl ashovers.<br />
When a fi re in its early development progresses to fl ashover,<br />
in theory, it is no longer possible for people in the building to<br />
survive. It is therefore very important to tackle the fi re before it<br />
reaches fl ashover. A very small percentage of all compartment<br />
fi res result in fl ashover. Firefi ghters must therefore have a basic<br />
understanding of the factors which affect the development of a<br />
compartment fi re, i.e. those factors that lead a fi re to fl ashover.<br />
4.1. Defi nition of fl ashover<br />
Flashover has been used as a concept for at least the last 40<br />
years. Its defi nition has been vague and over the last few years<br />
a number of different interpretations of this concept have<br />
arisen. Terms such as “rollover”, “lean gas combustion”, “spreadover”<br />
and “fl ameover” have been coined as substitute and/or<br />
complementary concepts, but without any agreed structure.<br />
Unfortunately, this means that there is a fair amount of scope<br />
for misunderstanding. It would be absolutely great if everyone<br />
could agree on the same defi nition (an ISO defi nition, for in-
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