Overpressure-neutre.pdf

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Protection of evacuation routes using a pressurisation systems to EN 12101-6

Pressurisation of evacuation routes Goal: set a pressure differential so that the pressure in the escape route is higher than the pressure in the fire affected space.

Goals for a pressurisation system

a) Means of escape: To maintain safe conditions in the protected areas during evacuation.

b) Fire fighting: To allow the fire brigade to access the building in safe conditions to locate victims and to locate the fire.

c) Protection of goods. It is important to avoid smoke getting into areas where vunerable goods or equipment or goods is located.

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Features of a typical bottom fed stair pressure differential system

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Alternative option to limit pressure to 60Pa Pressure relief damper to operate at 60Pa (max.) Pressurising oultlets distributed evenly vertically throughout the stair for buildings greater than 11m high. For buildings less than 11m, an outlet at the top of the stairs is normally acceptable Fire fighting stairs Accommodation area External leakage Pressurising air discharged at every level Maximum height between discharge is stairs to be no greater than 3 floor levels Fire fighting lobby access Fire zone Air release vents Fire service access level Single air intake position Smoke detector Motorised smoke damper Fire officer’s over rideswitch Duty standby pressurising units

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Fans in plant room in fire rated compartment (2 hour)

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Key 1 2 3 4

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Pressure relief damper to operate at 60Pa (max.) Fans in plant room in fire rated compartment (2 hour) Smoke detector Air intakes on opposite facades with smoke detectors and motorised dampers Duty standby pressurising units Alternative air intake Motorised smoke damper Air intake Alternative option to limit pressure to 60Pa Fire fighting stairs Fire fighting lift well (if required) Accommodation area External leakage Pressurising oultlets distributed evenly vertically throughout the stair for buildings greater than 11m high. For buildings less than 11m, an outlet at the top of the stairs is normally acceptable Fire fighting lobby Pressuising air discharged at every lobby level Maximum height between discharge is stairs to be no greater than 3 floor levels Fire zone Air release vent Fire fighting access Fire officer’s over rideswitch

System class

Examples of use

A

For means of escape. Defend in place.

B

For means of escape and firefighting.

C

For means of escape simultaneous evacuation

D

For means of escape. Sleeping risk

E

For means of escape phased evacuation.

F

For firefighting and means of escape.

Class A System For means of escape. Defend in place.

The design conditions are based on the assumption that a building shall not be evacuated unless directly threatened by fire. The level of fire compartmentation is such that it is usually safe for occupants to remain within the building. Therefore, it is unlikely that more than one door onto the protected space (either that between the stair and the lobby/corridor, or the final exit door) will be open simultaneously.

Class A System For means of escape. Defend in place.

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Differential pressure cirteria (all doors closed)

Flow rate criteria

Door open Door closed Air release path

Class B System For means of escape and firefighting.

A pressure differential system can be used to minimise the potential for serious contamination of firefighting shafts by smoke during evacuation and fire fighting operations. During firefighting operations it will be necessary to open the door between the firefighting lobby and the accommodation to deal with a potentially fully developed fire.

Class B System

For means of escape and firefighting.

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Differential pressure cirteria (all doors closed)

Flow rate criteria

Fire fighting stair Fire fighting lobbies Door open Door closed Air release path Door open (fire fighting lobbies Door closed (fire fighting lobbies Airflow from fire fighting lift shaft

Class C System

For means of escape simultaneous evacuation

The design conditions for Class C systems are based on the assumptions that the occupants of the building will all be evacuated on the activation of the fire alarm signal, that is, simultaneous evacuation. In the event of a simultaneous evacuation it is assumed that the stairways will be occupied for the nominal period of the evacuation, and thereafter will be clear of evacuees. Consequently, the evacuation will occur during the incipient stages of fire development, and some smoke leakage onto the stairway can be tolerated. The airflow due to the pressurisation system shall clear the stairway of this smoke. The occupants being evacuated are assumed to be alert and aware, and familiar with their surroundings, thus minimising the time they remain in the building

Class C System

For means of escape simultaneous evacuation

1 2 3 Differential pressure criteria (all doors closed)

Differential pressure criteria

Flow rate criteria

Door open Door closed Air release path

Class D System

For means of escape. Sleeping risk.

Class D systems are designed in buildings where the occupants may be sleeping, eg. hotels, hostels and institutional-type buildings. The time for the occupants to move into a protected area prior to reaching the final exit can be greater than that expected in an alert or able-bodied environment, and occupants may be unfamiliar with the building or need assistance to reach the final exit/protected space. Class D systems are also appropriate when the presence of a pressure differential system has served to justify the absence of a discounted stairway and/or lobbies that would normally be required under the national regulations.

Class D System

For means of escape. Sleeping risk.

1 2 3 Differential pressure criteria (all doors closed)

Differential pressure criteria

Flow rate criteria

Door open Door closed Air release path

Class E System

For means of escape phased evacuation.

Systems used in buildings where the means of escape in case of fire is by phased evacuation. a) In the “phased evacuation” scenario it is considered that the building would still be occupied for a considerable time whilst the fire is developing, creating greater amounts of hot smoke and gas. (This can vary greatly according to the type of materials, fire load involved and the geometry of the fire load). b) In the “phased evacuation” situation, the protected staircases shall be maintained free of smoke to allow persons to escape in safety from floors, other than the fire floor, at a later stage in the fire development

Class E System

For means of escape phased evacuation.

1 2 3 Differential pressure criteria (all doors closed)

Differential pressure criteria

Flow rate criteria

Door open Door closed Air release path

Class F System : For fire fighting and means of escape The system of differential pressure class F applies to minimise the chances of serious pollution by smoke in lobbies used by the fire brigade, both during the process of evacuation of people, and during the performance of such fire services. During Fire-fighting operations, the door between the area where the operations are being carried out and the accommodation area will need to be opened, to deal with a potential fire. In some situations it may be necessary to connect hoses to a riser outlet below the fire floor, and up through the stairs to the lobby of the fire floor. Therefore it is often not possible to close the doors between these lobbies and staircase, during the operation of fire extinguishing. If main exits to the stairs are found only in the interior of the Hall, or in the accommodation area in front of the halls, the door between the lobby and corridor or area of accommodation on the floor of the fire must stay open, during the operation of extinguishing.

Class F System : For fire fighting and means of escape

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Stair Lobby Accommodation Supply air Leakage through doors etc

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Air release Over pressure release vent 8 Accommodation 9 Lift lobby 10 Lift car

Airflow differences between systems Pressure difference criterion 50 Pa

Pressure difference criterion 10 Pa

Airflow criterion 0,75 m/S

CLASS A Defend in place

1,24 m3/s

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1,83 m3/s

CLASS C Simultaneous evacuation

1,24 m3/s

5,99 m3/s

2,10 m3/s

CLASS D Sleeping risk

1,24 m3/s

11,42 m3/s

7,51 m3/s

FANS Both situations (door closed and door open) should be considered

Airflow with doors closed In order to determinate the total airflow rate through leackages:

Q  1,5 0,83Ae  P1/ 2 DO

Air leakage data (door closed condition):

Type of door

Leakage area

Single-leaf opening into a pressurized space

0,01 m2

Single-leaf opening outwards from a pressurized space

0,02 m2

Double-leaf

0,03 m2

Lift landing door

0,06 m2

Air leakage data (door closed condition):

PRESSURIZATION

Air leakage data (door closed condition):

Calculation of the effective flow areas:

Ae

Door closed between stair and accomodation areas Ae = 8 x 0,01 = 0,08 m2 Calculation of the air leackage trouhg door closed ((QDC): QDC = 0,83 x Ae x P1/2 = 0,83 x 0,08 x 50 ½ = 0,469 m3/s Safey margin to consider other leackages

k1 = 1,5

Safety margin to consier leackages on ducts

k2 = 1,15

Calculation of airflow at door closed condition QSDC = 1,5 x 1,15 x 0,469 = 0,809 m3/s = 2,912 m3/h

FANS Airflow through the open door in the fire floor: Symplified method

- Airflow trough the open door in the fire level

Q  1,15 v  A D D - Airflow to blow in the stair in the door open condition:

Q  Q Q D DO DC

Airflow throuhg the open door in the fire floor: Symplified method

Airflow in the open door on the fire level

QDO

QD = 1,15 x 0,75 x 1,6 = 1,38 m3/s Airflow in the door closed condition:

QDC

QDC = 0,809 m3/s Airflow in door open condition:

QDO QSDO

QSDO = QDO + QDC = 1,38 + 0,809 = 2,189 m3/s = 7.880 m3/h

FANS Airflow throuhg the open door in the fire floor: Prescriptive method

Q  v A D D

Q LOB

Q

AVA  D 2,5

     0,83  Arem     

      

p US 1     2 

1 1     A2 A2 VA door 

  Q   DO      0,83 A VA  

1  p 2  LOB    

2 p

LOB

p US

  Q   DO      0,83 A door  

Q 1,15 Q SDO LOB

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Airflow throuhg the open door in the fire floor: Prescriptive method Airflow in the open door on the fire level

QDO

QDO = 0,75 x 1,6 = 1,2 m3/s Area of the air release

AVA

AVA = QDO / 2,5 = 0,48 m2

Pressure in the accomodation area

 QDO   1,2    PUS     0,83xAVA   0,83x0,48 2

PUS 2

   9,07 Pa  

QDO PUS

AVA

Area of the open door in the fire level:

Adoor

Adoor = 1,6 m2 Pressure in the stair:

PST

 QDO   PST  PUS    0,83xAdoor 

Arem

2

PST

2

 1,2  PST  9,07     9,07  0,81  9,88 Pa 0 , 83 x 1 , 6   Leackage area of doors closed: Arem = 0,08 m2

Arem

Adoo

Airflow leackage trouhg doors closed Qrem = 0,83 x Arem x (PST)2 = 0,83 x 0,08 x (9,88)1/2 = 0,209 m3/s Airflow to blow in the stair

QST

QST = QDO + Qrem = 1.2 + 0.209 = 1.409 m3/s Airflow to blow in the stair considering leackages on ducts: QSDO = 1,15 x QST = 1,15 x 1,409 = 1,62 m3/s =5,832 m3/h

QSDO

Example: EN 12101-6

FANS To control the differential pressure in the pressurised areas, one of the following methods should be used: - Dampers opening to the outside, to vent excess airflow (the airflow rate of the fan remains steady )

- Dampers in ducts, to create a by-pass. - Inverter to control the fan speed, to maintain a setpoint of 50 Pa via signal from a pressure sensor. Situation Doors closed Door open

Pressure

Fan speed

Airflow

50 Pa

Modulated

Modulated

Resulting

50 Hz

Maximum

STANDBY FANS When standby fans are required to maintain continuity in the event of a failure, the system should have either two fans and/or two motors to operate as duty/standby.

STANDBY FANS The standby fans should be of the same type and capacity as the duty fans. The switch between the duty fan and the standby fan should be automatic.

AIR INLETS Should be installed in a position where they will not be affected by a potential fire or by smoke. Usually fans, with the proprietary ductwork, if necessary.

AIR INLETS In case of risk of smoke entering the air inlet, two dampers provided with smoke sensors has to be installed so that if smoke is detected in one of the air inlets this is closed and the alternative one is open.

Installation options

ROOF

GROUND LEVEL

LOBBIES

Installation options ROOF

Test chamber MOTORIZED DAMPER To simulate opening/closing of doors, and leackages.

RF DOORS FAN

USE OF CFD • Dimensions STAIRCASE (High/Width/Depth): 30 x 6 x 4 metros • Dimensions LEVEL • High/Width/Depth): 3 x 10 x 12 metros • Doors: 1,62 m2 • Air release: 0,48 m2 • LEAK: 0,11 m2 • FIRE: HRRPUA=500 kW/m2

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• SMOKE T= 0 a 100 s (Cerrada)

T= 100 a 600 s (Abierta)

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• OVERPRESSURE T= 0 a 100 s (Cerrada)

T= 100 a 600 s (Abierta)

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• AIR VELOCITY T= 0 a 100 s (Cerrada)

T= 100 a 600 s (Abierta)

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• TEMPERATURE T= 0 a 100 s (Cerrada)

T= 100 a 600 s (Abierta)

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• VISIBILITY T= 0 a 100 s (Cerrada)

T= 100 a 600 s (Abierta)

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