DESIGN METHODS IN STAIRWELL PRESSURIZATION

Marion Meinert M.Sc.* & Univ.-Prof. em. Dr.-Ing. Wolfram Klingsch ** * Muenster University of Applied Science, Corrensstraße 25, 48149 Muenster, Germany

E-Mail: m.meinert@fh-muenster.de ** University of Wuppertal, Pauluskirchstraße 11, 42285 Wuppertal, Germany

E-Mail: klingsch@uni-wuppertal.de 1. Introduction Mechanical stair pressurization is a preferred system for staircases in high-rise buildings to control the smoke movement in case of fire though the survey conducted by Cowlard et al. [1] implies that pressurization systems fail in 9 out of 10 cases. Lay [2] stated that there is suspi-ciousness about the functionality among fire professionals. Requirements published in codes worldwide address the pressure difference to the adjacent floors or a minimum air inflow velocity into the fire floor by upper and lower bounds. The factors that influence the performance of the pressurization system in the stairwell are closely linked to the pressure profile along the flow path caused by the flow through the stairwell that pushes the smoke into the outside. Flow path resistances along this streamline and room pressures can be calculated by formulas that are derived from one dimensional fluid dynamical formulas like Bernoullis principle, the ideal gas law and using electrical resistance calculations, all of them are extended with empirical correlations. Those are the fundamentals for multizonal software like CONTAM [3] and state of the art of the performance based de-sign method of pressurized stairwells. The CFD code Fire Dynamics Simulator (NIST) [4] is used to highlight the limitations of the existing design methods by multizonal software [3]. 2. State of the Art Identified problems in the operation of stair pressurization are opening forces due to high pressure difference or entering the stairwell by the stack effect or failing of the evacuation concept resulting in too many open doors. The most fundamental parameter that is affecting the first is the estimation of leakage of the walls of the stairwell [2], while the performance of the pressurization fan depends on the latter and influences the pressure to open the doors. Worldwide different regulations exist that address those problems with thresholds for door opening force and required inflow velocity in stairwell door to fire floor as well as the number of open doors in the stairwell. Because the design of the peak flow rate of the fans depends on the number of open doors (according to design scenario) and due to internal pressure losses, there is a height restriction for single point injections. Those parameters should be tackled in stairwell regulations, table 1 shows that this is not the case for all of the observed codes. Additionally, design methods which are useful to achieve those requirements are named in some of them, e.g. in pr EN12101-13 analytical methods are described and the use of network models as well as CFD models are advised. 3. Physical Principle The factors that influence the performance of the pressurization system in the stairwell are closely linked to the pressure profile along the flow path caused by the flow through the stairwell that pushes the smoke into the outside. Flow path resistances along this streamline and room pressures can be calculated by formulas that are derived from one dimensional fluid dynamical formulas like Bernoullis principle, the Hagen-Pouiseulle flow for laminar flow through cracks, the ideal gas law and using electrical resistance calculations [5], all of them are extended with empirical correlations. Those are the fundamentals for multizonal software like CONTAM [3] and state of the art of the performance based design method of pressurized stairwells. Flow that is always three-dimensional can be mathematically described with the fundamental

equations of conservation of mass, of momentum (Navier-Stokes Equations) and conservation of energy. Together with the ideal gas law and simplifications to capture turbulence those are the foundations for computational fluid dynamics. For the realistic description of flow inside a building and its influence on the pressurization system it is essential to estimate flow paths and pressure losses along those flow paths in an accurate manner. Pressure losses affect the design and operation mode of the pressurization fan and therefore determine the maximum pressure differential via egress doors in the stairwell as well as the minimum critical velocity inside into the fire floor. Considering the building as completely sealed, and heated or cooled, due to the different tem-perature and accordingly different density a different gradient of the pressure head will be set up. When there is a connection between an opening in the enclosure at the first floor and at the top of the building in winter there will be a flow from the first floor through the building generally through the stairwell out of the top and in summer from the top to the bottom, which is regulated by the ratio of the opening areas and is well known as the “stack effect”. Addi-tionally the area of leakages through the building envelope and through the interior walls in-fluences this effect in combination with different temperatures due to cooling and heating of the floors and ventilation. According to the ideal gas law, e.g. a temperature rise of 1 K at STP leads to a pressure difference of 371Pa if it happens infinitely fast. This has no consider-able effect because the mass loss due to leakage during the heating process will prevent such an excessive pressure build up. But this stack effect can lead to a negative pressure on the lower floors of the stairwell and subsequently supports smoke entering the stairwell while doors to the upper floors could be pressurized and prevent people entering in winter. The above mentioned climatic phenomenon together with the pressure losses affect design and operation mode of the pressurization fan and therefore determine the maximum pressure differential via egress doors in the stairwell.

Table 1 International Requirements

Code Scenario Design criteria Design methodologyNFPA 92 -2012 USA

vestibules permitted >8 stories: multiple injection requires hBuilding>15m / 3stories

∆pmin= 12.5 Pa Fmax,opening= 133N Opposed airflow dependent on fire size

Analysis requ. for hBuilding

>30.5 m with single- inject., for complex sys-tems computer network model recommended

MHRRL Germany

hBuilding >22m: pressurized stair-well requ., vestib. equ., pressure relief in fire floor

udoor = 0.75-2 m/s Fmax,opening = 100N

-

TRVBS 112 Austria

Resid. floor door open; Evac. door in fire & 1st fl. open; Fire fight. d. in fire & 1st fl. open

udoor = 1 m/s (fire floor) udoor = 1 m/s (fire floor) udoor = 2 m/s (fire floor)

-

DIN EN 12101-6

Air release paths required, classification of buildings to nature and usage, specific de-scription of scenarios

udoor = 0.75 - 2 m/s ∆pmin= 10-45-50 +- 10 Pa Fmax,opening = 100N

Electrical resistance anal-ogy

prEN 12101-13 draft

hBuilding >22m – supply every 6th floor

udoor = 1 - 2 m/s ∆pmax = 60 Pa ∆pmin = 30 Pa Qmin = 7.500 – 15.000 m³h-1

Analytic. calc. or CFD-mod.; zone-knots model-ing necess. for build. h > 60 m, E- resist. analogy

UAE Fire and Life Safety Code of Practice

hBuilding >23m pressurized stair-well required, for >8 stories: multiple injection requires hBuilding 15m / 3stor., vestibules permitted

∆pmin = 12.5 / 25 Pa ∆pmax = 60 Pa Fmax,opening = 133N udoor = 0.75 - 2 m/s

-

4. Pressure induced Flow & Pressure Loss Airflow is induced by a pressure difference. From duct design the pressure drop or loss of total head is well known: It is an internal flow loss in useful flow energy (mechanical energy) that is converted due to internal friction of the air molecules into heat (internal energy) ac-cording to the first law of thermodynamics (dissipation). Dissipation increases in turbulent flow where increased internal friction takes place. In the fundamental conservation equations of fluid dynamics, this dissipation could be impli-cated by splitting the conservation of energy into a part for mechanical and one for heat ener-gy [11]. While the conservation equations describe all the flow phenomena at different places and different times in detail, the well known Bernoulli Equation approximates the flow effects that take place between rooms of different pressure or while the stairwell is flown through to some points at one streamline at one specific time. Between two points it is given by

2122

2212

11 22 lossphguphgup (1)

With known conditions at point 1, the pressure loss has an influence on the velocity pressure and therefore on the mass flow rate at point 2 and has to be considered carefully in design of the pressurization system because supply fans perform dependent on the summated pressure losses on the flow path. In contrast, because pressure loss is caused by friction, it is dependent on the velocity or the Reynolds number. Consequently there is a feedback between supplied volume flow in the staircase and created pressure loss on the flow path that is governed by local velocities. In engineering, different approaches exist to consider the pressure loss, for the wall friction this is for example illustrated in the Moody chart, local resistances or head loss coefficients are experimentally determined by the measured ratio of pressure loss between two points to velocity pressure of a reference point: C [12], K [11]or [13] (eq. 2) The related velocity is closely linked to the considered flow area and can be determined with mass conservation by ureference=Q/Areference. For common duct fittings loss coefficients are listed in fundamental liter-ature [13-15] and are tabularized, printed in curves or can be calculated by equations depend-ent on velocity or Reynolds number and geometrical parameters of the fitting.

2

21

2

21 2

2u

p

u

pKC lossloss

(2)

5. Pressure Losses in Stairwells Internal pressure losses that occur during the flow through the stairwell have a great influence on the design of the pressurization system and are strongly influenced by the geometry. 1976 Shaw and Tamura [16] related the overall pressure to the Darcy-Weißbach-equation for friction in a rectangular duct where the pressure loss depends on an empirically determined friction factor SWK (eq. 3), an equivalent hydraulic diameter Dh= 4A/P=4·a·b/2/(a+b) and the

height of the floor. Additionally, an approach was introduced to relate the pressure loss to an empirically determined equivalent orifice area for the stairwell Ao (eq. 4) based on the Ber-noulli equation, which represents the flow resistance by an orifice at each floor level. Here the coefficient Cd for turbulent discharge of an orifice completes the equation. This approach was also used by Achakij [17] whose experiments were the basis for today’s design methods and his findings are a part of the contemporary design procedure [5].

static pressure P1

velocity pressure P1

gravitational pressure P1

pressure loss

static pressure P1

velocity pressure P2

gravitational pressure P2

Other approaches where introduced by Poreh et al. [18] and [19], who relate their experiments to the initial loss coefficient floorSW , per floor (eq. 5) while [20-23] use the effective area with

odeff ACA (eq. 6).

2321 22

)(Q

A

bahKp

SW

hloorSWloss

(3)2

2221 2

1Q

ACp

od

loss

(4)

22

,21 2

QA

pSW

floorSWloss

(5) 2

2

2

21 2

1

2Q

AA

AA

Qp

eff

SW

effSW

loss

(6)

Besides the flow rate or the mean velocity related to the stairwell area, the complexity of ge-ometrical dependencies of the pressure loss varies significantly. While the use of the friction factor SWK requires the input of width, length and height of the stairwell, for the approach

referring to the equivalent orifice area and the flow coefficient floorSW , it is sufficient to spec-

ify the stairwell area. The empirical coefficients are additionally related to open and closed treads [17], shape (conventional with 2 landings vs. helical with 4 landings [18] ), the exist-ence of railing, existence and size of well hole or running length [20-23]. In 2003 Poreh et al.[18] figured out by experimental studies, that the geometry of the stairwell (conventional vs. helical) has a great influence on the flow resistance. The fact that persons inside the stairwell have a significant effect on the pressure drop was observed in 1988 by Achakij [17], though further tests with additional parameters were not carried out since then. Nevertheless the effect of pressure losses is not considered in perfor-mance based codes at all. In table 2 loss coefficients that are determined by different approaches are compared in terms of the scenario of a stairwell 5m length, 3m width and 3m height with the volume flow of 4m³/s related to a critical velocity of 2m/s through a door (1m x 2m).

Table 2 Determination of pressure losses [16],[17],[18],[23] &[22],[21], [20],[19] 

 

0

1

2

3

4

5

6

7

8

min

max

min

max

min

max

high resistance

low resistance

min

max

wide w

ell hole

narrow w

ell hole

no well hole

closed well hole

min

max

min

max

nopersons

persons model model 1:6 model 1:6 model1:10

realscaleTamura& Shaw

1976

realscaleAchakij

1988

Poreh &Trebukov

2000

IMTECH2012

pr EN 12101 -13 Ostertag2001

Gerhardt&

Konrath2001

pre

ssu

re lo

ss p

er f

loor

[p

a] 4

m³/

s lx

w=

3x5m

6. Pressure Losses on Flow Path Pressure drop that occurs on the flow path at the floor from stairwell to the envelope has to be considered for the pressurization design as well as internal pressure losses inside the stairwell. In fire safety engineering, pressure loss appears in multizonal software like CONTAM as it affects the mass flow between two nodes. Options for describing airflow paths include power law models, orifice models or two-way flow models that address thermal induced flow via an opening. Each model deals with different empirically determined loss coefficients. For the orifice model, the Bernoulli equation (1) rearranges for the geometrical opening area with openingopeningopening uAQ for isothermal conditions and the assumption that no height dif-

ferences occur for an opening that connects two rooms (nodes / pressure zones) to:

2,

22

,2121 22

geometry, openinglocaldopeningopening

localdopeningloss uCQ

A

Cupp

(13)

Here the loss coefficient founds input into the velocity pressure (dynamic pressure) that is related to the mean velocity of the opening and calculated by mass balance and can be related to the orifice equation as well as to the mass flow between two nodes of different pressure:

21

21

,

, pAC

uACm opening

locald

openingopeningmassd (14)

Hence it is obvious that according to equation (15) there is a relation between the local loss coefficient and the mass discharge coefficient which is used to relate the geometrical opening area to the real flow area due to contraction. For simplification the velocity inside the rooms is assumed to be negligible small. This does not meet the physics in terms of pressurization systems, e.g. the critical velocity of 2 m/s in a door (1 m x 2 m) corresponds to a velocity of 0.10 m/s in a common room width of 10 m and a height of 2.2 m. Because the empirical models are mainly tailored for thermal or wind induced flow and not for mechanical induced flow in rooms with high mass exchange rates, their applicability for pressurization systems is not yet validated. One point are missing experiments on the deter-mination of the local or mass discharge coefficient for the flow through doors. Literature val-ues state Cd,mass to be typically close to 0.6 for a sharp-edged orifice and slightly higher for other openings in buildings [3]. Klote [5] suggest for open doors in stairwells Cd,mass = 0.35 though it is recognized that stationary vortices may reduce the flow significantly. According to recent studies, it is very difficult to determine loss coefficients for external openings in wind driven ventilation [24]. Additionally Chu et al. [24] pointed out that internal openings have a significant effect on the ventilation rate as they trim down flow velocity and an internal coefficient of Cd,loca l= 2.58 respectively Cd,mass = 0.62 for wind driven ventilation was derived though their findings are tied to a fixed flow path. 7. Spatial Resolution: Electrical Resistance Concept Spatial distribution and local pressure losses due to flow patterns in a room govern the distri-bution of mass flow via different openings in one room. This has an influence on the real flow path and is essential to determine pressure loss resistances for the design of the fan, because in multizonal models the pressure loss depends on the mass flow through an opening. According to the program documentation of the predecessor to CONTAM, AIRNET [29] as well as ac-cording to Klote [5] the distribution of flow between multiple openings can be calculated sim-ilar to the electrical resistance concept (Kirchhoff’s law) of resistance in parallel and series. While in CONTAM laminar flow is considered with the laminar flow coefficient K, in turbu-

locald

massdC

C,

,

1 (15)

lent flow it is the turbulent flow coefficient C. Here Klote [5] uses the effective area concept (table 3). 8. External Pressure Losses Nevertheless loss coefficients are widely used in engineering, recent studies [30],[31] show that the application of multiple local resistances in duct design does not meet the real pressure losses. This is because pres-sure loss does not occur within the fitting under observation but as well upstream and downstream. For flow through rooms in-duced by a pressurization system this effect is reinforced due to more complex flow phenomenon. An isothermal FDS simulation was run to visualize the influence of the outflow and inflow conditions on flow path resistance. While the multizonal and analytical ap-proach integrates pressure losses due to dissipation in one loss coefficient, the CFD tool FDS simulates pressure losses for every point in the flow path by Navier-Stokes equations and dy-namic Smagorinsky turbulence model in detail. Figure 1 shows the flow through one door (1m x 2m) between two rooms in a 3m height compartment. The inflow conditions (4m³/s - 2m/s - 1m x 2m) are established by a door positioned a) parallel (direct flow) and b) rectangu-lar to the door under observation (crossflow). Additionally the inflow and outflow conditions are varied with room size of 10m in flow direction to 10m width (room) versus 4m width (corridor). Cell sizes of x·y·z=0.05m·0.05m·0.05m were determined as optimum mesh size by a sensitivity study. Figure 1 visualizes the flow pattern through the different inflow conditions by velocity magni-tude; red color indicates high velocities of >3m/s while blue indicates 0m/s. It can be ob-served that local velocities are much higher (>3m/s) than calculated mean velocities from mass balance (2m/s). Consequently there exist different flow patterns for the scenarios that lead to different distri-butions of pressure drop. Everywhere in the room, where a current is set up, a pressure drop is created and intensified in regions with steep velocity gradients. For instance in the scenarios with rectangular inflow conditions pressure drop is also caused by the flow that occurs within the room far away from inflow or outflow door. The magnitude of pressure drop via the door between the rooms / corridors shows a difference of 3.5Pa for the considered scenarios (simu-lated in the middle of the door on the longitudinal axis of the room in a height of 1m). The resulting pressure drops of approx. 3Pa and 6.5Pa correspond to a flow coefficient of 0.89 respectively 0.60 according to equation (2) and cover a wide range. For smaller flow rates e.g. 1 m³/s (corresponding to a velocity of 0.5 m/s through a door 1m x 2m) the pressure drop is about half an order of magnitude and varies between 0.28 and 0.33 Pa. For the determination of a flow coefficient in the examined scenarios, it should be considered that the flow coeffi-cient of the jet flow from the inflow door interacts with the flow coefficient of the observed door between the rooms. Hence smooth inflow conditions via the full room width, not through a door are additionally visualized for the direct flow scenario (dashed line). According to fig-ure 1, the inflow condition through a door that causes a highly turbulent flow behavior within the room can be able to mitigate the pressure loss of a door in comparison to smooth inflow condition.

Multizonal Approach - CONTAM [29]

LA

MIN

AR

pKm (18)

parallel:

ie KK (19) series:

ie KK

11 (20)

TU

RB

UL

EN

T pCm

parallel:

ie CC (21) series:

22

11

ie CC (22)

Analytical Approach - Klote [5]

parallel:

ie AA (23) series:

2/1

2

1

ie A

A (24)

Table 3  electrical resistance concept 

Derived flow coefficients are in the range of 1.25-2.71 for Cd, local and 0.89-0.60 for Cd,mass referring to a flow rate of 4m³/s and to the flow rate of 1m³/s in the range of 1.67-2.2 for Cd, local and 0.77-0.67 for Cd,mas .The latter correspond very well to the loss coefficients of 0.68-0.73 suggested by Steckler in 1985 for fire induced mass loss coefficients through windows and doors [32].

Figure 1 Flow pattern through a door Q=4m³/s, A=2m² 

FDS was used to demonstrate the behavior of flow via multiple resistances. As it can be seen in figure (2) flow does not necessarily distribute equally via 3 resistances of the same size as it is calculated with CONTAM. Distances and positions between inflow and different outflow elements have a significant influence on the distribution of mass flow within the 3 rooms, especially the set-up of a free jet flow determines the mass distribution. Figure 3 illustrates the flow distribution in terms of fraction mass inflow in room to mass outflow through 3 openings. Regarding the distribution and distance of inflow and outflow elements, figures (4) and (6) confirm this behavior. In this simulation an “eccentric set-up” was chosen. However due to other flow pattern the difference between mass flows via the openings decreases slightly. Ad-ditionally the influence of different opening sizes (1.5m x 1m vs. 0.3m x 0.5m) that leads to different flow resistances is investigated (figure 5).

It is figured out that the eccentric inflow conditions in the room and hence the formation of a free jet have a great influence on the mass distribution via the both openings, this is not repro-duced with CONTAM modeling. However, the change of resistance due to changed opening size within the flow path and centric flow distribution lead to the same results (figure 6). On the other hand for suction out of the room scenario the comparison of FDS and CONTAM show nearly no differences except in the modeling of the change in opening size (figure 7).

9. Pressure Losses and Flow Paths within a Stairwell The discrepancies between empirically determined pressure losses inside the stairwell with

  a) room direct flow

a) corridor direct flow

b) room crossflow b) corridor crossflow

IN

IN

OUT OUT

 

Figure 2 Flow visualization for flow through 3 

rooms 

 

Figure 3 Mass distribution for flow through 3 

rooms 

 

Figure 4 Flow visualization for flow through 2 

rooms ‐ eccentric 

 

Figure 5 ‐ Flow visualization for flow through 

2 rooms –centric with changed resistance 

 

Figure 6 Flow through 2 doors ‐ over pressure 

 

Figure 7 Flow through 2 doors ‐ under 

pressure 

O1 O2 O3

O1 O2 O1 O2

respect to their importance obey the need for further investigation. For this purpose, a simula-tion study with the Fire Dynamics Simulator was carried out. Here, two types of stairwells where examined: one conventional stairwell with two landings, and one helical stairwell with four landings as it was suggested by Poreh [18] (figures 8-11). Geometrical variation re- garding well hole is taken into account. Furthermore a closed railing and a simple handrail are compared. Different flow paths through a 30 m high stairwell (hfloor = 3.75m) with one door open on the top floor are examined. Additionally a scenario with two open doors is consid-ered, one on the top and one on the middle floor with varying position (a-e in Fig. 12, 13).

 

Figure 8 FDS model           

2 landings – closed well 

hole 

 

Figure 9 FDS model               

4 landings – closed railing 

 

Figure 10 plan view stairwell 2 

landings 

 

Figure 11 plan view stairwell 4 

landings 

During the investigation the pressure distributions on the landing are compared. All simula-tions have a volume flow of 4m³/s, which corresponds to a (mean) velocity of 2m/s in a door of 2m². Regarding figure 12 it can be observed that there is a great discrepancy between the pressure losses caused by different geometries. Here the helical stairwell spans the widest range, confirming Poreh’s observation of the smallest pressure loss for an open well hole. Both stairwells have the lowest pressure drop when the flow is guided through the well hole via a closed railing. The influence of leakages was studied likewise. Leakages through tight and loose walls as well as through gaps of one door were summarized in the gap below a door with Atigh = 0.003 m² vs. Aloose = 0.02m² (located at position d according to figure 10). Figure 13 shows that the leakage area has a great influence on the pressure relief with height, never-theless the influence of mass leakage is comparatively small. For tight walls a mass loss of 3% was observed, for loose walls a value of 10% results.

b

a 

b c d 

a

IN IN

Figure 12 Influence of stairwell geometry on 

pressure drop 

Figure 13 Influence of wall leakage for 

stairwell with 2 landings and closed well hole 

The influence of door position inside the stairwell with multiple open doors has also a great influence. Figure 14 shows that the mass flow rate through the top door, that should be 2.4 kg/s (20°C, u = 1m/s) for a uniform distri-bution, is reduced up to 60 % depend-ing on the door position (a-e accord-ing to figures (10-11). Hence also the mean velocity through the top door decreases to 0.6 m/s while the mean velocity through the middle door in-creases to 1.4 m/s. In summery the internal flow path and internal pres-sure losses have a great influence on flow distribution and accordingly the attained inflow velocity into the fire

floor.

10. Current Design Criteria The design criteria that affect the pressurization systems, the thresholds for door opening force versus minimum pressure difference to the floors to avoid smoke from floors entering through leakages of the wall and the critical inflow velocity require further investigation: Be-cause the stairwell ventilation state has a significant effect on the heat release rate in the floor (open doors below and above the fire floor) [33], the interaction between fire and flow through the stairwell should be part of the performance based design. Likewise the applicabil-ity of the critical ventilation velocity as a principal parameter in tunnel design with a similar approach to stairwell pressurization was questioned recently by Vaitkevicius et al. [34]. It was discovered, that local flow phenomena in tunnels also have a significant impact on the spread of smoke that could not be captured by one critical design value. Hence the pressurization concept could not be described with a simple balance of smoke flow (low pressure side) ver-sus critical velocity (high pressure side).

Figure 14 Influence of door position on flow distribution inside the stairwell 

11. Conclusion For pressurization systems, airflow patterns inside the stairwell as well as across doors control the quantities of interest: the pressure drop due to dissipation caused by internal friction which increases with intensity of turbulence. Available coefficients are tied to fixed scenarios and may be suitable for ventilation purpose but in pressurized case with higher flow rates, veloci-ties and dissipation effects need to be expanded. Additionally the electrical resistance analogy concept used for flow distribution does not take into account the complex geometry of the flow. Especially the formation of free jets in rooms can lead to strong deviations between model and reality, which does not appear when flow is caused by suction. For modern open plan scenarios this effect could be captured by the im-plementation of additional analytical relations for free jets or the coupling of CFD with multi-zonal models [35]. It is essential that the designer knows about those limitations and is sensi-tive to the degree of accordance between multizonal modeling and real flow behavior. The quantification of air leakage paths and leakage areas with common flow coefficients for realistic calculation of the pressure profile due to stack effect is nearly impossible to meet by designers: First of all measured and tabularized values have a wide range and engineering judgement is very difficult for one certain building, secondly building leakage is determined on the construction side and varies per building in every floor. Only with field measurements under operating conditions the designer will be able to identify real leakage in detail. Additionally, pressure fluctuations due to wind effects on the building as well as the uncer-tainties associated to the nature of the fire [1] lead to a highly transient flow behavior that cannot be represented by steady-state correlations. Prétrel et al. [36] showed that within the first 5 minutes of the fire in a confined and force ventilated enclosure there was a huge pres-sure variation measured that was affected by the fire size, the ventilation features and the en-closure characteristics like the conductivity possibility of the walls or the air flow resistance of the ventilation system (flow inversions in the ventilation branches). This can only be in-cluded by transient CFD calculations depending on fire size. Furthermore, factors that influence the pressure profile at doors to the fire room are not yet completely understood e.g. air pumping effect of room fires which is related to the size of the room openings in relation to the heat released [37]. Hence for the safe design of a pressurization system it is of crucial importance to define pres-sure drops on the flow path and furthermore ensure that flow paths are build-up and kept in a fire scenario. This should also be implemented in fire management and the evacuation con-cept. Human influence in case of unintended closing and opening of doors can significantly affect the pressurization system and need to be considered in design. Additionally the influ-ence of human beings in the flow path resulting in greater pressure losses needs to be studied further. 12. References 1. Cowlard, Adam, et al. Fire Safety Design for Tall

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