Upp í vindinn - 01.05.2009, Side 37

Evaluating the fire safety performance
In order to check the safety in a conservative
way, it is necessary to simulate cases when fire
safety devices fail or unexpected problems
occur. Statistics show that smoke exhaust
systems fail to start and to work properly in
roughly 20 % of cases. In addition, it often
happens that one emergency exit door remains
closed. Therefore, the combination of these 2
failures remains a likely scenario which will be
simulated.
Results from fire simulation
As discussed earlier, the main concern for
evacuation purposes is the visibility. It is
important that it remains above Vrit at z = 2
meters from the floor. In addition, the visibility
is also checked at the height of 6 meters for
the people standing at the top of the stands.
Figure 2 (left) shows the visibility in a cross
section containing the fire. It shows a very
clear two-layer condition, with fresh air close
to the floor and hot smoke above.The visibility
remains acceptable after 10 minutes at ground
fioor level, but is under critical value at the
top of the stand. Figure 2 (right) shows a top
view of the visibility at z = 2 meters from the
floor shown after 12 minutes. At this time, the
visibility is poor mainly on the left side and
above the stand.
In addition to visibility slices, visibility probes
are positioned in the center of the hall and
above the stand. They give the time evolution
of the visibility at certain heights (see Figure
3), allowing the determination of the time
when the visibility becomes critical at z = 2 m
and z= 6 m above the floor, shown in Table 1.
The visibility is also calculated in the case the
smoke exhaust system fails to start and vents
do not open.
As shown by these results, the visibility
becomes critical after 12:30° minutes on the
ground floor and after 5:30° minutes at the
top of the stands, when the smoke exhaustion
system works properly. When the vents remain
closed, these critical times fall to 8:30° and
Figure 3:Time evolution of the visibility at the center with and without smoke exhaustion system working.
4:40° minutes respectively.
Evacuation simulation
The fire and smoke spread simulation has
allowed the determination of the critical times,
when complete evacuation must be achieved.
The owner wishes to accept 3500 people on
the skating ring (zone 1) and 600 on the first
t„i,(min.)
Probe position [Visibility <10 m]
c E z = 2m,middleofhall 12:30°
01 r- > >< z = 6m, above stand 5:30°

1/1 o P z = 2m,middleofhall 8:30°
z S z = 6m, above stand 4:40°
Table 1 :Time to critical visibility
floor (zone 2). Characteristics of the occupants,
such as walking velocity, size and agility are set
to be consistent with a young population from
20 to 35 years, who are most likely to attend a
rock concert.
The time to be aware of the fire t is estimated
aw
to be 50 sec. and the reaction time t to be 50
reac
sec. Therefore, a total response time will be t
' r resp
= t + t = 100 sec.
aw reac
The safety can be assessed by considering the
K
safe
t
evac
Figure 1: FDS model of Skautahöllin (left). Fire and smoke visualization after 3 minutes (right).
factor K ,, defined as the ratio between the
evacuation time and the critical time:
If K r < 1, the safety level is not sufficient.
If Ksafc > 1, the safety level is sufficient.
However, it is necessary to consider a certain
security delay to take into account unexpected
problems such as panic or longer reaction
time, and how familiar the occupants are with
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