Cristian Rdulescu
Student, Master ADS, Facultatea de Construcii
Raul Zaharia
Profesor, Facultatea de Construcii, Departmentul CMMC
Comparison between
different methodologies to
calculate the thermal
action in fire situation
using EN1991-1-2
Introduction
The paper presents the methodology to calculate the fire load density using
Annex E of EN1991-1-2, together with the specific provisions of the German
and Dutch National Annexes. A study case for a library was performed, in order
to emphasize the differences between the three approaches.
Geometrical data:
Length = 75 m
Width = 40 m
Height = 5 m
Architectural aspects:
3 doors (2 m x 2.8 m)
One 75 m glass facade
Procedure
To assess the results obtained by the European Standard EN 1991-1-2,
and via the Dutch NEN-EN 1991-1-2 and the German DIN EN 1991-1-2
National Annexes respectively, OZone software was used, taking into
consideration input data such as geometry, occupancy and firefighting measures.
An overview of all three standards shows that the values of certain factors
involved in the computation of the design fire load density are subject to change
and there are also different calculation procedures.
The relevant tables of Annex E from EN 1991-1-2 subjected
to modification within the National Annexes
Table E.1: Factors taking into account the fire activation risk due to the size
of the compartment and the fire activation risk due to the type of occupancy;
Table E.2: Factors taking into account the different active fire fighting
measures, generally imposed for life safety reasons;
Table E.4: Fire load densities for different occupancies;
Table E.5: Fire growth rate and rate of heat release for different occupancies
(the value of the fire growth rate t [s] is the same for all countries).
The European Standard EN 1991-1-2
E.2 tab. with ni factors from the EN
Automatic
Fire
Suppressio
n
Automat
ic Water
Extinguis
hing
System
Independe
nt Water
Supplies
0
1
2
Automatic
Fire
Detection
Automati Automati
c fire
c Alarm
Detectio Transmissi
on to
n
Fire
& Alarm
Brigade
Manual Fire
Suppression
Work
Fire
Briga
de
Off
Site
Fire
Briga
de
Safe
Access
Routes
Fire
Fighti
ng
Devic
es
Smok
e
n6
n7
n8
n9
n10
0,78
0,9 or 1 or
1,5
1,0 or
1,5
1,0 or
1,5
Exhau
st
Syste
m
by
by
Heat
n1
n2
n3
0,61
1,0 0,87
0,7
0,87
Smok
e
n
4
0,73
n5
0,87
0,61
The Dutch National Annex NEN-EN 1991-1-2
E.1c tab. with pni factors from the NEN
Measures
Case
Multiplier
(regarding the
failure
probability) of
active fire safety
measures
normal
1 independent water supply
2 independent water suplies
heat
smoke
pni
0,02
0,01
0,005
0,25
0,0625
automatic alarm
transmission
(to the fire fighting brigade)
0,25
0,1
fire fighting brigade
public fire fighting brigade
private fire fighting brigade
(with support of public fire
fighting brigade)
sprinkler
detection
Observation
0,02
The failure probabilities are related to fire safety
facilities whose operation is guaranteed by regular
The German National Annex DIN EN 1991-1-2/NA:2010-12
Safety measures
A different aspect is the fact that the automatic detection and the automatic
alarm transmission to the fire brigade are considered by default.
The risk of fire activation in DIN EN is given by:
Pfi = P1 x P2 x P3
(5)
in which:
P1 is the probability of at least one initial fire per year, according to
the building category
P2 is the reduction factor depending on the fire brigade type and on the time
between alarm and firemen intervention
P3 is the reduction factor regarding automatic fire detection (by smoke or
by heat), automatic transmission of the alarm, sprinkler systems are present
BB.4 tab. From DIN with the failure probability factors p2,2 and p3
Measures
Failure
probability by
case
p2,2
p3
1
1
1a
1b
2
2a
2b
3
3a
3b
3c
Public fire brigade with
arrival time
< 15 min
> 20 min
Work fire brigade
< 10 min (four squadrons)
< 10 min (two squadrons)
Automatic extinguishing
system
VdS/CEA Standard sprinkler
system
other sprinkler system
other water extinguishing
0,2
0,5
0,02
0,05
0,02
0,05
Comparative results
EN 1991-1-2
With smoke exhaust
system
Without smoke
exhaust system
Automati
c water
extinguis
hing
system
Automat
ic fire
detectio
n by
smoke &
automat
ic alarm
transmis
son to
the fire
brigade
On
site
fire
fighti
ng
briga
de
Off
site
fire
fighti
ng
briga
de
1166
X
X
X
-
X
X
X
-
X
X
X
X
X
X
-
1186
1222
1253
1217
1247
1276
NEN-EN
1991-1-2
Maximum Obtained Maximum Obtaine
Temperature
at
Temperatu d at
[minutes
re
[minute
[ C ]
]
[ C ]
s]
121
0
1242
1271
1300
1267
1292
1316
1336
DIN EN 19911-2
Maximum
Temperatur
e
[ C ]
Obtaine
d at
[minute
s]
66
74
1057
77
1339
83
69
77
87
76
85
98
11
83
95
120
93
107
126
150
1057
1057
1226
1057
1238
1294
77
77
87
77
79
102
1514
1530
1547
N/A
N/A
N/A
97
104
115
N/A
N/A
N/A
Conclusion
Because of the differences within the three approaches, as expected, there are
signifficant differences for the results as well.
The European Standard shares similar values with the Dutch National Annex
especially in the cases where there are at most 2 active firefighting measures ,
but when there are 3 active measures taken, results show significant differences
both in terms of maximum temperature and time.
The German National Annex offers significantly higher values, greater than
the ones obtained with the European Standard and the Dutch National Annex.
THANK YOU FOR YOUR ATTENTION!
