The fire load density used in calculations should be a design value, either based on measurements or in special cases based on fire resistance requirements given in national regulations.
The design value may be determined:
— from a national fire load classification of occupancies; and/or
— specific for an individual project by performing a fire load survey.
The design value of the fire load is defined as:
(Eq. 3‐35) where:
• is the characteristic fire load density per unit floor area [MJ/m²] (see f.i. Table E.4)
• is the combustion factor equal to 0,8
• is a factor taking into account the fire activation risk due to the size of the compartment (see Table E.1)
• is a factor taking into account the fire activation risk due to the type of occupancy (see Table E.1)
• is a factor taking into account the different active fire fighting measures i (sprinkler, detection, automatic alarm transmission,
firemen,…). These active measures are generally imposed for life safety reason (see Table E.2 and clauses (4) and (5)):
.
For the normal fire fighting measures, which should almost always be present, such as the safe access routes, fire fighting devices, and smoke exhaust systems in staircases, the values of Table E.2 should be taken as 1,0. However, if
Compartment floor area Af [m2]
Danger of Fire Activation q1
Danger of Fire
Activation q2 Examples of Occupancies
25 1,10 0,78 Art gallery, museum, swimming pool
250 1,50 1,00 Offices, residence, hotel, paper industry
2500 1,90 1,22 Manufactory for machinery & engines
5000 2,00 1,44 Chemical laboratory, painting workshop
10000 2,13 1,66 Manufactory of fireworks or paints
Table 3.2 From table E.1 - Factors , .
evaluation copy
-Topic: User’s Manual/Verification tests - EN1991-1-2_(c).xls page 39
EUROCODES SPREADSHEETS STRUCTURAL DESIGN
SECTION3 EUROCODE 1 EN 1991-1-2 ANNEX C, ANNEX E
these fire fighting measures have not been foreseen, the corresponding value should be taken as 1,5. If staircases are put under overpressure in case of fire alarm, the factor of Table E.2 may be taken as 0,9.
CHARACTERISTIC FIRE LOAD. It is defined as:
(Eq. 3‐36)
where:
• is the amount of combustible material [kg], according to (3) and (4)
• is the net calorific value [MJ/kg], see (E.2.4)
• is the optional factor for assessing protected fire loads, see (E.2.3).
CHARACTERISTIC FIRE LOAD DENSITY. It is defined as:
(Eq. 3‐37)
where is the floor area of the fire compartment or reference space.
NET CALORIFIC VALUES. Net calorific values should be determined according to EN ISO 1716:2002. The moisture content of materials may be taken into account as follows:
(Eq. 3‐38) where:
• is the moisture content expressed as percentage of dry weight
• is the net calorific value of dry materials.
ni
Material Hu Material Hu Material Hu
wood 17,5 Alcohols 30 Polyvinylchloride, PVC (plastic) 20
cellulosic materials
20 Fuels 45 Bitumen, asphalt 40
carbon 30 Pure
hydrocar-bons plastics
40 Leather 20
Paraffin series
50 ABS (plastic) 35 Linoleum 20
Olefin series
45 Polyester (plastic) 30 Rubber tyre 30
Aromatic
Table 3.3 Net calorific values Hu [MJ/kg] of combustible materials for calculation of fire loads.
evaluation copy
-EUROCODES SPREADSHEETS STRUCTURAL DESIGN
SECTION 3 EUROCODE 1 EN 1991-1-2 ANNEX C, ANNEX E
page 40 Topic: User’s Manual/Verification tests - EN1991-1-2_(c).xls
RATE OF HEAT RELEASE Q. The growing phase may be defined by the expression:
(Eq. 3‐39)
where:
• is the rate of heat release [W]
• is the time [s]
• is the time needed to reach a rate of heat release of 1 MW.
The parameter and the maximum rate of heat release , for different occupancies, are given in Table E.5. These values according to Table E.5 are valid in case of a factor (see table E.1).
For an ultra-fast fire spread, corresponds to 75 s. The growing phase is limited by an horizontal plateau corresponding to the stationary state and to a value of
given by where:
— is the maximum area of the fire which is the fire compartment in case of uniformly distributed fire load but which may be smaller in case of a localised fire
— is the maximum rate of heat release produced by of fire in case of fuel controlled conditions (see Table E.5).
The horizontal plateau is limited by the decay phase which starts when 70% of the total fire load has been consumed. The decay phase may be assumed to be a linear decrease starting when 70% of the fire load has been burnt and completed when the fire load has been completely burnt. If the fire is ventilation controlled, this plateau level has to be reduced following the available oxygen content, either automatically in case of the use of a computer program based on one zone model or by the simplified expression:
Occupancy Fire growth rate t [s] RHRf [kW/m2]
Dwelling Medium 300 250
Hospital (room) Medium 300 250
Hotel (room) Medium 300 250
Library Fast 150 500
Office Medium 300 250
Classroom of a school Medium 300 250
Shopping centre Fast 150 250
Theatre (cinema) Fast 150 500
Transport (public space) Slow 600 250
Table 3.4 Fire growth rate and RHRf for different occupancies (from Table E.5).
Q 106 t
evaluation copy
-Topic: User’s Manual/Verification tests - EN1991-1-2_(c).xls page 41
EUROCODES SPREADSHEETS STRUCTURAL DESIGN
SECTION3 EUROCODE 1 EN 1991-1-2 ANNEX C, ANNEX E
(Eq. 3‐40) where:
• is the combustion factor
• is the net calorific value of wood with
• the opening area
• is the mean height of the openings [m].
When the maximum level of the rate of heat release is reduced in case of ventilation controlled condition, the curve of the rate of heat release has to be extended to correspond to the available energy given by the fire load. If the curve is not extended, it is then assumed that there is external burning, which induces a lower gas temperature in the compartment.
3.3 Verification tests
EN1991‐1‐2_(C).XLS. 7.20 MB. Created: 12 February 2013. Last/Rel.-date: 12 February 2013. Sheets: member: ; emissivity of the fire: ; surface temperature(1) (mean value) of the member (beam), say: ; coefficient of heat transfer by convection:
(1) The surface temperature results from the temperature analysis of the member according to the fire design Parts 1-2 of prEN 1992 to prEN 1992 to prEN 1996 and prEN 1999, as relevant.
m t
evaluation copy
-EUROCODES SPREADSHEETS STRUCTURAL DESIGN
SECTION 3 EUROCODE 1 EN 1991-1-2 ANNEX C, ANNEX E
page 42 Topic: User’s Manual/Verification tests - EN1991-1-2_(c).xls
Solution: The natural fire model of a localised fire is used. Flame length:
evaluation copy
-Topic: User’s Manual/Verification tests - EN1991-1-2_(c).xls page 43
EUROCODES SPREADSHEETS STRUCTURAL DESIGN
SECTION3 EUROCODE 1 EN 1991-1-2 ANNEX C, ANNEX E
evaluation copy
-EUROCODES SPREADSHEETS STRUCTURAL DESIGN
SECTION 3 EUROCODE 1 EN 1991-1-2 ANNEX C, ANNEX E
page 44 Topic: User’s Manual/Verification tests - EN1991-1-2_(c).xls
Solution: For the determination of the fire load density the Annex E of EN 1991‐1‐2 offers a calculation model. The design value of the load density may either be given from a national fire load classification of occupancies and/or specific for an individual project by performing a fire load evaluation. At this example, the second method is chosen. From Table E.1 for compartment floor area up to : , . From table
E.1 and clauses (4) and (5): , , , ,
, . Therefore, we get:
Table 3.5 Amount and characteristics of combustible materials.
250 m2 q1 = 1 50 q2 = 1 00
evaluation copy
-Topic: User’s Manual/Verification tests - EN1991-1-2_(c).xls page 45
EUROCODES SPREADSHEETS STRUCTURAL DESIGN
SECTION3 EUROCODE 1 EN 1991-1-2 ANNEX C, ANNEX E
(factor ). Maximum area of the fire compartment equal to . Opening area ; mean height of the openings: . Find the time at which the growing phase is limited by the horizontal plateau corresponding to the stationary state.
[Reference sheet: Annex E]‐[Cell‐Range: A174:O174‐A309:O309].
Solution: From Table E.5 (“Fire growth rate and RHRf for different occupancies”):
, .
The growing phase may be defined by the expression:
.
Case a): the fire is fuel controlled.
The growing phase is limited by an horizontal plateau corresponding to the stationary state and to a value of Q given by:
. Horizontal plateau starts at (see plot above):
. RHRf = 250 kW m 2 q2 = 1 0
Afi = 70 m2 Av = 10 m2 heq = 1 80 m
t = 300 s RHRf = 250 kW m 2
Q 106 t
t
----
2
=
Figure 3.19 Growing phase limited by the horizontal plateau: the fire is fuel controlled.
Qmax = RHRfAfi = 250 70 = 17500 kW = 17 5 MW
t t 1000 RHR fAfi 106
--- 300 1000 250 70
106
--- 1255 s 21 min
= = = =
evaluation copy
-EUROCODES SPREADSHEETS STRUCTURAL DESIGN
SECTION 3 EUROCODE 1 EN 1991-1-2 ANNEX C, ANNEX E
page 46 Topic: User’s Manual/Verification tests - EN1991-1-2_(c).xls
The horizontal plateau is limited by the decay phase which starts when 70% of the total fire load has been consumed. The decay phase may be assumed to be a linear decrease starting when 70% of the fire load has been burnt and completed when the fire load has been completely burnt.
Case b): the fire is ventilation controlled.
In this case the plateau level has to be reduced following the available oxygen content, either automatically in case of the use of a computer program based on one zone model or by the simplified expression E.6 given in Annex A of EN 1991‐1‐2. At this example, the second method is chosen:
. Horizontal plateau starts at (see plot above):
.
When the maximum level of the rate of heat release is reduced in case of ventilation controlled condition, the curve of the rate of heat release has to be extended to correspond to the available energy given by the fire load. If the curve is not extended, it is then
Figure 3.20 Growing phase limited by the horizontal plateau: the fire is ventilation controlled.
Qmax MW = 0 10 m H uAv heq
Qmax MW = 0 10 0 8 17 5 10 1 80 = 18 78 MW
t t 1000 Q maxkW 106
--- 300 1000 18780
106
--- 1300 s 22 min
= = = =
evaluation copy
-Topic: User’s Manual/Verification tests - EN1991-1-2_(c).xls page 47
EUROCODES SPREADSHEETS STRUCTURAL DESIGN
SECTION3 EUROCODE 1 EN 1991-1-2 ANNEX C, ANNEX E
assumed that there is external burning, which induces a lower gas temperature in the
example-end compartment.