Enclosure fires

6.6 Risk assessment
There are obviously risks involved with tackling a ventilationcontrolled
fi re. These situations can be very risky and unfortunately,
it is not always easy to detect the warning signs. It is
diffi cult to know what will happen before we enter the room.
But the more warning signs there are indicating a backdraught,
the higher the chance that this has occurred. If the signs are
not very clear some of the other scenarios may occur.
At this point, we need to refer back to the section on
fl ashovers, where we discussed the colour of smoke gases in
detail. The smoke gases’ colour can sometimes be used as an
indicator of an imminent backdraught. But the smoke gases’
colour cannot be used as the only indicator. If this is combined
with a number of other indicators, we can get a clear
idea as to whether there is any danger of a backdraught occurring.
The crucial factor with regard to backdraughts is air.
A number of signs indicating an imminent backdraught
are described below.
6.6.1 Warning signs
It is important to carry out thorough risk assessments, both
before and during an ongoing operation. The indicators below,
taken together, should be regarded as warning signs for
Figure 104. Smoke gases
are escaping out of a
building, but there are no
fl ames visible. The fi re
offi cer in charge refl ects on
what he can do.
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