Stairwell Lift Pressurization Calculations
Stairwell Lift Pressurization Calculations
Stairwell Lift Pressurization Calculations
SMOKE CONTROL
BY
PRESSURISATION
CONTENTS
PAGE NO:
Summary
Chapter One
5-6
Chapter Two
Why Pressurisation?
7-8
Chapter Three
9 - 16
Chapter Four
17- 20
Chapter Five
Fan Selections
21- 27
Chapter Six
28 - 29
Appendix One
References
30
ACKNOWLEDGEMENTS
The author wishes to acknowledge the assistance he received from Mr Cyril Moss,
KG Smoke Dispersals Ltd and Mr E Gorden Butcher of Fire Check Consultants with
the preparation of this paper.
3
SUMMARY
There are basically two main methods for controlling smoke in buildings to
prevent it contaminating escape routes - by Ventilation and by Pressurisation.
Fans for Fire Smoke Venting (Ref 1) examines the motivation behind the
increased use of Powered Ventilators for the exhausting of hot smoke from
fires and determines their requirements and specifications.
This paper undertakes a similar task to determine the requirements and
specification for FANS IN PRESSURISATION SYSTEMS, based on the
requirements of BS5588 Part4:1998.
CHAPTER 1
a) Door Velocity
Fire induced forces create pressure differences across doors etc, which allow smoke
to flow through any gaps present.
- VELOCITY
BS5588 Part 4 - 1978 was revised and reissued during April 1998
In addition, BS5588: Part 4: 1998 incorporates the Pressurisation System requirements for Fire Fighting
specified in
BS5588: Part 5 1991 and it is still this requirement - 2.0m/sec with up to THREE EFFECTIVE DOORS OPEN which produces
the greatest air supply demand.
The discussion and calculations in this revised paper are now based on the requirements of BS5588: Part 4: 1998.
Code
Pressure (Pa)
Min.
Max.
Door Velocity
No. Of Effective
Open Doors
U.K.
BS5588
Part 4:1978
50
0.75 m/sec
ONE
BS5588
Part 5:1991
Not
Relevant
2.00 m/sec
Australia
AS1668
P.1
50
110
1.00 m/sec
Singapore
CP13
50
110
1.00 m/sec
Canada
N.B.C.C.
1990
No Mention
4.72 m3/sec +
0.094 m3/sec
For every door
U.S.A.
U.B.C.
1988
37
N.F.P.A.
(92A) 1988
up to
45
U.K.
BS5588
50
Part 4: 1998
60
133
60
No Mention
No Mention
No Mention
No Mention
CHAPTER 2
Why Pressurisation?
Major development work on Axial Flow Fans
for the venting of hot fire smoke was carried
out during the 1980s (Ref 4), which led to
the publication in 1990 of a test standard
BS7346 Part 2 (Ref 5).
-VE
-VE
-VE
-VE
-VE
Fire Floor
Staircase
Lift
Lobby
Accom.
Pressurising Air
2.3 PRESSURISATION
However, it is possible to hold back smoke
from a fire by simply supplying clean air into
the escape routes, thereby developing excess, or POSITIVE pressure in the spaces
requiring protection.
+VE
+VE
+VE
Fire Floor
+VE
Staircase
Lift
Lobby
Accom.
The use of Pressurisation for SMOKE CONTROL began to be considered during the
1950s, both in the U.K. and Australia.
CHAPTER 3
Staircase
Accomodation
Pressurising
Air Supply
Exhaust Air
(Powered)
Exhaust Air
(Natural)
+ 50 Pa
Fire Floor
Staircase
Lift
Lobby
Accom.
Area of use
Residential, sheltered housing
and buildings designed for three door
Fire Floor
protection (Fig 5)
B
Open
0.75 m/sec
simultaneous evacuation)(Fig 7)
D
Staircase
Accom.
TABLE 2 - Classification of
Buildings for Smoke Control using
Pressure Differentials
10
Fire Floor
2.0 m/sec
Open
Open
Staircase
Lift
Lobby
Accom.
11
Fire Floor
Open
0.75 m/sec
Staircase
Accom.
+ 10 Pa
Fire Floor
Open
Staircase
Accom.
12
Fire Floor
Open
0.75 m/sec
Open
Staircase
Accom.
+ 10 Pa
Fire Floor
Open
Staircase
Accom.
13
Open
Fire Floor
Open
0.75 m/sec
Open
Staircase
Accom.
Open
Open
+ 10 Pa
Fire Floor
Open
Staircase
Accom.
14
This can be achieved by one of four methods:a) Via the leakage provided by the window
cracks on the outside of the building.
In practice this is unrealistic. The area provided is unlikely to be sufficient.
b) Through automatically opened windows
or vents around the perimeter of the
building.
This is a possibility where the area concerned has sufficient outside wall space to
accommodate the vent area necessary.
Operating Mode 2 would require almost 0.5
m2 of vent area on every floor for each pressurised staircase.
Powered Vent
Natural Vent
Damper
15
LEVEL 2
Plant ON - running continuously at REDUCED capacity - except in an emergency.
(TWO STAGE PRESSURE SYSTEM).
Accom.
Stairs
Simple Lobby
Fig 11 - Staircase With Simple Lobby
Lift
Lift
Lobby
Two duct systems, from a common fan, required both for STAIRCASE and LIFT
LOBBY, used where the LOBBY provides
outlets from LIFTS, contains TOILETS or
other ancillary rooms Fig 12.
Accom.
Stairs
Fig 12 - Staircase With Lift Lobby
Lift
Lift
Lobby
Corridor
Extending the LOBBY pressurisation system into the CORRIDOR using additional
outlets in the corridor Fig 13. Used only
where the construction of the corridor has a
fire resistance of 30 minutes or more.
Stairs
Fig 13 - Stairwell With Lift Lobby & Corridor
d) LIFT SHAFT
Generally only used in Fire Fighting
(BS5588 Part 5). The LIFT LOBBY then
effectively becomes a simple lobby as far as
the staircase pressurisation system is concerned. With the lift shaft pressurised there
is no escape path for the air via the lift shaft.
The STAIRCASE and LIFT SHAFT can be
pressurised using a common fan with separate ducting.
16
CHAPTER 4
The design of any air movement system involves an answer to the question:How do I establish the AIR VOLUME
required to make this system work?
With a Pressurisation System designed for
SMOKE CONTROL there is an initial question to be answered.
1
n
1
2
Building Height
(m)
Fire Pressure
(Pa)
Wind/Stack Effect
(Pa)
8.5
8.0
25
25
8.5
10.5
25
50
8.5
13.0
50
100
8.5
19.5
50
150
8.5
29.5
50
Design Pressure
(Pa)
Type of Door
Size
Crack
Length (m)
Leakage
Area (m2)
2 m x 800 mm
5.6
0.01
2 m x 800 mm
5.6
0.02
2 m x 1.6 m
9.2
0.03
Lift Door
2 m High x
2 m Wide
8.0
0.06
For single openings, one door, AE = nett free area of the opening.
For several openings, or doors, situated in PARALLEL around a pressurised space Fig 11.
AE = A1 + A2 + A3 + A4 ...
Accomodation
A2
A1
Lift
Lobby
+VE
Stairs
+VE
Fig 14 - Doors In Parallel
18
Accomodation
Lift
A3
Lift
A4
For several opening - or Doors - situated in SERIES along an escape route - Fig 12.
AE =
1 + 1 +
(A2)2
(A1)2
1 +
(A3)2
1
(A4)2
-1/2
For two doors in series more typical of a pressurisation system this simplifies to
AE =
Accom.
(A1 x A2)
(A12 + A22)
A4
1
2
Stairs
+VE
A1
A2
A3
b) Fire Fighting
During fire fighting the Fire Brigade need to
open doors on the fire floor to gain entry
without themselves being engulfed in
smoke. The code of practice specify that an
Air Velocity of 2.0m/sec is needed to
achieve this.
4.6 REQUIREMENTS OF A
PRESSURISATION SYSTEM
c)
20
CHAPTER 5
Fan Selections
5.1 WORKED EXAMPLE
a) The addition of 50% to the calculated airflows at MODE 1.
The best method for establishing the requirements of SUPPLY FANS for pressurisation systems is to select the fans for a
typical pressurised staircase.
The example chosen is perhaps the simplest form of a Pressurised Staircase for
Smoke Control, and as such may be unreal.
However, using a simple example, it is
easier to determine and highlight the fan
requirements.
At the time of writing neither of these specifications are in line with the high temperature
categories specified in BS7346 Part 2 or the
Hence designers are recommended to seek
clarification from Building Control.
21
5.4
Double
Doors
Accomodation
Stairs
AE = 1 + 1
A22
A12
6 Floors
--1/2
--11/2/2
1 + 1
1.62 0.482
1.2
0.83 x 0.46
= 0.46 m2
A = 1 x double door at 0.03 = 0.03 m2
6 x single doors at 0.01 = 0.06 m2
0.09 m2
1/
Q = 0.83AEP 2
1
= 0.83 x 0.09 x 50 /2
Increase by 50%
P1 =
Q
0.83 x AE
= 10.01 Pa
= 0.53m3/sec
+ 0.26 m3/sec
0.79 m3/sec
Say 0.80 m3/sec
= (2.0 - 0.8)
= 1.2m3/sec
Q
1/
2
0.83 x P
=
V = 0.75 m/sec
P0
0.83 x (50)
= 0.204 m2
P1
P0
Door
Closed
Open
Staircase
Accomodation
Open
Fig 17
A=
=
V=
Q=
1.2
1/
2
Exit vent
A= Q
2.5
10 Pa
Door
Open
Staircase
Accomodation
Fig 18
22
1/
2
= 0.83 AE P
= 4.20 m3/sec
= 0.83 x 1.6 x 10
1
A
-1/2
+ 1
2
1
1.6
+
2
-1/2
1
0.22
= 1.6 m2
= 0.75 m/sec
= 1.20m3/sec
AE =
= 0.217 m2
1
Q = 0.83 AE P /2
1 + 1
A12 A22
-1/2
1 + 1
1.62 0.482
1.2
0.83 x 0.458
-1/2
= 0.458 m2
2
P1 =
1/
2
= 0.83 x 0.217 x 10
Q
0.83 x AE
= 0.57 m3/sec
= 10.01 Pa
(Say 10 Pa)
Q = 0.83 AE P 2 1/2
= 0.83 x 1.6 x 10
= 4.20 m2/sec
= 1.14 m3/sec
= 0.80 m3/sec
6.14 m3/sec
2. VELOCITY CRITERION
Open
V = 0.75 m/sec
P0
Exit vent
A= Q
2.5
P1
P0
Door
Open
1/
2
0.83 x (P)
Staircase
= 4.20 m3/sec
= 1.02m2
Accomodation
Fig 19
23
1/
0.83 x (50) 2
5.14 m3/sec
Add MODE 1
0.80 m3/sec
9.14 m3/sec
a) To calculate pressure required in stairwell to exhaust 3.2 m3/sec to atmosphere via fire floor (Fig 20).
V = 2.0 m/sec
P0
Exit vent
A= Q
2.5
1
0.83 x (50) /2
P1
P0
=
Door
Open
8.34
1
0.83 x (50) /2
1.421 m2
Accomodation
Fig 20
Area of single leaf stair/fire room door
= 1.6 m2.
Area of exhaust vent from fire room
= 3.2/2.5 = 1.28 m2
AE = 1 + 1
A22
A1 2
-1/2
= 1 + 1
1.62 1.282
-1/2
= 1.0 m2
2
P =
Q
0.83 x AE
3.2
0.83 x 1.0
Exhaust
1
Q = 0.83 AEP /2
Fire Fighting and Escape Staircase 3.2 m3/sec at exhaust system losses
or 1.28 m2 of Natural Vent per Floor.
= 0.83 x 1.6 x 15
/2
= 5.14 m3/sec
24
The air duty requirements detailed at Paragraph 5.5 are calculated with the pressurising airflow exhausting from the fire floor
through a natural vent. This results in an
increased airflow through the open fire door
to outside.
The amount of air to be wasted via the pressure relief damper would fall to 6.4 m3/sec,
thereby reducing the size of the PRESSURE RELIEF DAMPER from 1.43 m2 to
1.09 m2.
Woods JM Aerofoil
40JM/16/2/28
500
Chart 1
Pa - 1
400
Point A
Pa - 2
300
MODE 2 - CLASS A
200
100
Point B
MODE 1
50
X
0
1
2
Volume Flow (m3/sec)
25
50
Woods JM Aerofoil
80JM/25/4/32
Pa - 2
500
14
400
40
rpm
Chart 2
Pa - 1
MODE 2
(CLASS E)
300
Pa - 3
MODE 3
(CLASS B)
200
69
50
MODE 2
(CLASS A)
MODE 1
rp
100
50
X
6
5
7
8
Volume Flow (m3/sec)
10
11
12
The amount of air to be wasted would now reduce to 4.8 m3/sec (Dimension X + Y) demanding a pressure relief damper 0.82 m2 in area.
The fan speed is maintained eliminating the
dangers inherent with speed reduction.
26
600
Woods JM Aerofoil
50JM/20/2/6/30
Two fans in parallel
Pa - 2
Pa - 1
Chart 3
500
One fan
running
400
Two fans
running
Pa - 3
MODE 3
(CLASS B)
MODE 2
(CLASS E)
300
200
100
MODE 2
(CLASS A)
MODE 1
50
50
X+Y
0
10
11
Again the fan speed is maintained eliminating the dangers inherent with fan
speed reduction. As an added advantage, using Varofoil, the fan will tend to
correct for any unidentified leakage etc
in the staircase and system.
Pa 1
Pa 2
600
Pa 3
500
Chart 4
400
Mode 3
CLASS B
300
Mode 2
CLASS E
200
100
Mode 2 - CLASS A
Mode 1
50
50
0
12
700
6
5
7
8
Volume Flow (m3/sec)
8
5
12
6
16
7
x+y
27
20
8
24
9
10
28
11
32
12
CHAPTER 6
The requirements of both SUPPLY and EXHAUST fans in Pressurisation Systems can
be listed as follows:-
Within the limits imposed by the general requirements of a supply air fan, providing for
variable air duty can best be achieved by
one of the following methods.
a) Supply Air Fans must be capable of volume variation to meet the demands of
all three operating modes of the system.
This is discussed in more details under
paragraph 6.2
Constant speed fans ensure that the maximum pressure capability of the fan is available at all three operating modes of the
system.
28
The need for STAND-BY FANS in a Pressurisation System is a function of two considerations.
a) The degree of fire risk.
b) The reliability of the fan equipment.
The degree of fire risk must of course be
determined by the relevant fire and building
control authorities.
The discussion in this paper shows that current fan engineering technology is well able
to provide the requirements of both SUPPLY and EXHAUST AIR FANS of a PRESSURISATION SYSTEM for SMOKE
However, in spite of these findings, they recognised that, in FIRE SAFETY SYSTEMS,
RELIABILITY is of PARAMOUNT IMPORTANCE and warranted the provision of
STAND-BY FANS.
29
APPENDIX ONE
References
1. J.A. Wild
2. J.H. Klote
An overview of Smoke
Control Technology
3. P.H. Thomas
Movement of Smoke in
Horizontal corridors
against an airflow.
Institution of Mechanical
Engineers Paper C401/016
March 1990.
5. BS7346 Part 2
6. P.J. Hobson
L.J. Stewart
7. BS5588 Part 4
8. BS5588 Part 4
9. BS5588 Part 5
Seminar at Woods of
Colchester Ltd.
February 1993.
This document has been produced as a general guide and its contents should not be construed as any
representation on our part as to the quality or fitness of our products for any particular purpose, nor as
providing advice on the design of fire and smoke control systems. You are recommended to consult your
professional advisers on matters relating to the design and installation of any such systems.
30
Ref: WTP 41
31