Fire safety Sprinkler systems
B1 Fire is extinguished using
Outcome
first aid fire fighting techniques
Fire out
A Fire starts
in room
Flashover
B2 Fire not extinguished
Figure 1: Illustration of fire development stages prior to flashover
occurring in a non-sprinklered compartment
sizes when sprinklers are used in schools, assembly
B1 Fire is extinguished using
Outcome
first aid fire fighting techniques
and recreation buildings, and manufacturing spaces.
Fire out
A probabilistic approach requires calculation of
the likelihood of a fully developed compartment
A Fire starts
C1 Sprinkler system
fire occurring. For a compartment with and without
in room
operates
Fire out
sprinklers, this can be done relatively easily using
event trees. Event trees assume fires will develop via a
B2 Fire not extinguished
series of discrete stages and that each different stage Flashover
C2 Sprinkler system
will produce a number of subsequent events, such as:
fails to operate
‘fire burns out of its own accord’; ‘fire spreads beyond
one material item’; and so on. The event trees used
Figure 2: Illustration of fire development stages prior to flashover
in this analysis are illustrated in figures 1 and 2. This
occurring in a sprinklered compartment
analysis technique is comparative, so it is hoped that
any inaccuracies in these simple event trees will cancel
out.
Heating conditions
The heating conditions within the fire compartment
Start simulation
then need to be determined. This stage is more difficult
to quantify, due to uncertainties in fire load quantities
and the rate at which ventilation enters the room
Get fire load value Get room
when glazed elements fail. In the case of windows,
[kg/sq m] dimensions [m]
for example, the proportion of glass that shatters will
Get compartment Get ventilation
depend on numerous factors – such as the thickness insulation properies condition
and type of glass, the type of frame and the quality
of workmanship. Uncertainties like these can be
Get fire resistance data
addressed using Monte Carlo simulations.
Loop
Iterate through parametric fire
A probabilistic approach requires Does temperature on
unexposed face exceed 140C
calculation of the likelihood of a
fully developed compartment fire Store result – then loop
occurring
Fail = Fail + 1
The main benefit with Monte Carlo simulations is
that the embedded calculations are based on physical
Figure 3: Illustration of Monte Carlo
theory and experimental measurement. This helps
simulation process
compensate for a lack of information about real fires in
a manner that other risk methods cannot. Furthermore,
assumptions made within the analysis are explicit –
which means that the sensitivity of these assumptions
can be measured. This is achieved by changing the
values for each variable, re-running the same set of
simulations, and then comparing the new results with
those originally generated. >
www.cibsejournal.com March 2010 CIBSE Journal 51
CIBSEMar10 pp50-51,52,54 feature_fire.indd 51 2/25/10 5:38:59 PM
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