Fire safety Sprinkler systems
0.11
0.10
30 minutes fi re resistance
60 minutes fi re resistance
0.09
The main benefi t with Monte
90 minutes fi re resistance
0.08 Carlo simulations is that the
0.07
embedded calculations are based
0.06
F
requency
on physical theory and experimental
0.05
0.04
measurement
Relative
0.03
0.02
> recreation buildings with sprinklers. This is fi ve times
0.01 greater than the 4,000 sq m called for in Approved
0 Document B. In manufacturing-type buildings,
0 2500 5000 7500 10000 12500 15000 17500 20000 Approved Document B requests that compartments
Floor Area m
2
with sprinklers are restricted to a 14,000 sq m area, yet
the graph indicates that a compartment size of 60,000
Figure 8: Assembly and recreation – risk of
sq m could be reached before precise equivalency is
compartmentation failure versus compartment size
attained.
The data in these fi gures assume that the sprinkler
system will fail only fi ve per cent of the time. Using
0.13
Microsoft Excel, it’s very simple to determine how the
0.12
30 minutes fi re resistance
60 minutes fi re resistance
results will change when a higher sprinkler failure
0.11
90 minutes fi re resistance
0.1
probability is used. The outputs in fi gure 10 show how
0.09
the results generated for a school may change when
0.08
the sprinkler system failure rate is increased to 0.1 [10
0.07 per cent], 0.2 [20 per cent] and 0.3 [30 per cent] for
F
requency
0.06
a 60-minute fi re resisting enclosure. This means of
0.05
accounting for reliability is one of the main benefi ts of
Relative
0.04
using a probabilistic approach.
0.03
0.02
Conclusions
0.01
0
Current compartment sizes stem from the
0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 55000 60000
recommendations made in the Fire Grading of Buildings
Floor Area m
2
Report published in 1946. This publication does not
thoroughly explain the thinking behind current area
Figure 9: Manufacturing – risk of compartmentation
limits; however, it does state that ‘a proper solution
failure versus compartment size
to the issue of compartment size limitation requires
extensive statistical analysis and the data needed for
such a study is not available at the current time’.
0.01
Sixty years on, robust statistical data still don’t exist.
However, the restriction this imposes on design is
less severe. This is because computational, risk-based
0.008
design approaches of the type described here can be
used to generate statistical data via simulation.
0.006 Design techniques of this type are starting to gain
widespread acceptance. For example, the BRE tool
F
requency
CRISP III, which uses a similar approach, was recently
0.004
used to justify open-plan sprinklered apartments. In
Relative
other studies, sprinklers have been used as a substitute
0.002
5% sprinkler failure
for passive fire protection in low-rise steel-framed
10% sprinkler failure
buildings and to derive new fi re-resistance periods for
20% sprinkler failure
30% sprinkler failure
UK buildings.
0
Probabilistic methodologies can be used to
0 2000 4000 6000 8000 10000 12000
compare the performance of any fire engineered
Floor Area m
2
design. However, if used to promote the inclusion of
Figure 10: Risk of compartmentation failure versus
sprinkler systems in buildings, by justifying signifi cant
sprinkler success rate – schools
reductions elsewhere, a sharp reduction in annual UK
fi re losses would most certainly result. ●
Craig English and Sam Bennett are fi re engineers at
Hoare Lea
54 CIBSE Journal March 2010 www.cibsejournal.com
CIBSEMar10 pp50-51,52,54 feature_fire.indd 54 2/25/10 5:39:23 PM
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