Post on 03-Jun-2018
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David Purser
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Institution of Fire Engineers 2009 AGM Conference and Exhibition
1-2 July 2009
Human Fire Behav iou r
- and Per fo rmance Based Des ign
Prof. David PurserHartford Environmental Research
Visiting professor: Universities of Greenwich, Bolton and Maryland
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David Purser
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Why should a fire engineer consider
human behaviour? Because life safety in fire depends on escape time which is greatly affected by
aspects of human behaviourAvailable Safe Escape Time > Required Safe Escape Time by an appropriate safety margin
Benefits of understanding human behaviour: Enables improved design to better reflect the needs of occupants
e.g. useless to design a building:
with four expensive escape stairs if occupants will always use only the one
they came in by an alarm sounder that occupants ignore because they dont believe it
represents a fire, or that is activated late because it depends on the actionof a badly trained security guard
Enables accurate calculations of escape time, taking into account
quantitative data for all different phases of RSET
Good behavioural design not only makes evacuation more efficient, but
decreases the uncertainties in escape time calculations increasingconfidence in performance based design
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David Purser
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Basic thesis
Behavioural responses of individuals to alarms or seeing fires can be complex and
unpredictable, especially time to start evacuation (pre-movement time)
For groups of people, pre-movement times become more predictable, depending mainly on
a few key qualitative features relating to the nature of the occupants and the type of
occupancy (e.g. office, hotel, airport) and their normal activities. These can be classified
into a small set of design behavioural scenarios for which quantitative data (pre-
movement time distributions) can be measured.
Times for travel phase of evacuation can be calculated from physical parameters (occupant
numbers and densities, escape route dimensions, walking speeds) but a small set ofbehavioural parameters (wayfinding, exit choice, merge behaviour) is also important
Well designed systems have a high level of affordance for occupants. This means that
warnings and staff guidance should be clear and encouraging, so occupants are motivated
to respond, and emergency exits should be attractive giving occupants confidence and
motivatation to use them (e.g. emergency exits part of normal circulation routes, green
flashing lights no signs saying alarmed emergency exit do not use)
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David Purser
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About British Standard PD7974-6This lecture centres on PD7974-6 which contains a method developed for
RSET design calculations applicable to a range of different premises. Also:
ISO/TR 16738 an international version about to be published
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David Purser
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Escape time formula
RSET (?tesc) = ?tdet + ?ta + ?tpre + ?ttrav
(RSET) depends upon:
Time from ignition to detection (? tdet )
Time from detection to general alarm (? ta )
Evacuation time, which has two phases
Pre-movement time (time from alarm to when occupants begin
to move towards the exits) ? tpre
Travel time (the time for occupants to travel to a place ofsafety) ? tpre
Total egress for each customer leaving a Restaurant
0
10
20
30
40
50
60
70
1 2 3 4 5 6 7 8 9 10 11
Individual Customers (1-11)
Time(seconds)
Flow Time
Response Time
Pre-movement Time
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David Purser
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Time to detection and alarm
Level A1 alarm system: Automatic detection activating immediate general alarm
?ta = 0 Alarm time effectively zero
Level A2 (two stage) alarm system: Automatic detection providing a pre-alarm to security,
manually (or automatic time-out delay) activated general alarm. Alarm time should be takenas the fixed delay. For a voice alarm system add message time x 2
?ta = time out delay (usually 2 or 5 minutes)
Level A3 alarm system: Local automatic detection and alarm near the fire or no automaticdetection with manually activated general alarm.
?ta = likely to be long and unpredictable
Time to automatic detection calculated from fire dynamics
Time to alarm depends on system may include behavioural aspects
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David Purser
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Pre-movement process
Pre-movement process
Starts at alarm or cue - ends when travel to exit
begins.
Has two components:
Recognition - starts at alarm or cue ends with
first response
Response - starts at first response - ends with
travel to exit
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David Purser
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Pre-movement processesRecognition: occupants continue with pre-alarm activities
e.g. Working, Shopping, sitting, eating, watching football
Response: occupants carry out a range of activities:Investigative behaviour to find source of fire
Stopping machinery, securing money or other risks
Gathering children and other family members (for example who have gone to the toilets)
Wayfinding
Alerting others
Fighting fire
Passivity
Relative action sequences
Dwellings
0
10
20
30
40
50
60
70
80
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4
Relative action number
Frequency
Investigate
Mitigate fire
Help others
Call for help
Other
Passive
Wait for help
Collect items
EscapeGo for help
All people who reported a "get
out" action, N=80
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David Purser
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Evacuation time
For a population of occupants both pre-movement and travel
follow time distributions
? tPre = ? tPre(first occupants) + ? tPre(occupant distribution)
Variable delay followed by a log-normal distribution
Frequency distribution of pre-movement times
0
2
4
6
8
10
12
00:00 00:20 00:40 01:00 01:20 01:40 02:00
Time (seconds)
Frequency
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David Purser
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Main qualitative and quantifiable aspects
The main qualitative features used to define the scenarios are :
Occupant alertness (awake or sleeping) Occupant familiarity (familiar or unfamiliar) Single or multi-enclosures
Further qualitative features influencing response times in any particular scenario:
? Alarm system? Spatial complexity
? Fire safety management system
These are classified into three levels of performance
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David Purser
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Table 1: Design behavioural scenario categories
Category Occupantalertness
Occupantfamiliarity
Occupantdensity
Enclosures/complexity
Occupancy type (ADB purposegroups)
A Awake Familiar Low One or many Office or industrial (3,6,7a)
B1
B2
Awake
Awake
Unfamiliar
Unfamiliar
High
High
One or few
One with focal
point
Shop, restaurant, circulation space (4)
Cinema, theatre (5)
Ci
Cii
AsleepLong term:individualoccupancy.Managedoccupancy:
Familiar Low Few Dwelling (1a-c)Without 24 hour on site management.
Serviced flats halls of residence etc
Ciii Asleep Unfamiliar Low Many Hotel, hostel (2b) D Medical care Unfamiliar Low Many Residential (institutional) (2a)
E Transport Unfamiliar High Many Railway station Airport (5)
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David Purser
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Occupant behaviourTime from ignition
(min.sec)
Fire visible on camera approximately half metre flame height. Customersees fire and warns shop assistant who investigates and goes to fetch fireextinguisher.
Assistant fighting fire with extinguisher, flame height approximately 1metre, fire quite large, fails to extinguish and moves away
All this time people are entering the shop, passing the fire, shopping andwaiting at the checkout to pay for goods
Shop filling with smoke, people reluctant to leave shopping
People evacuating thought thick smoke
Staff evacuating
A few people occasionally re-enter near doorway
Front doors shut from outside
0.19
1.19
1.19-3.30
3.30
4.00
4.15
4.00-5.00
5.00
Sequence of events in clothing store
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David Purser
HER
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David Purser
HER
Food hall pre-movement time distribution
0
2
4
6
8
10
12
14
16
18
0 20 40 60 80
Tine (seconds)
Personsstartingper5seconds
0
0.05
0.1
0.15
0.2
0.25
Fractionofpopulationper5seconds
freq
Series2
Customers ignore sounder but well-trained staff achieve efficient evacuation
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David Purser
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Total egress for each customer leaving a Restaurant
0
10
20
30
40
50
60
70
1 2 3 4 5 6 7 8 9 10 11
Individual Customers (1-11)
Time(seconds)
Flow Time
Response Time
Pre-movement Time
Spokenmessage begins
Shopping centre evacuation
behaviour measurements
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? Location out of view of camera. Occupant position guessed
* Re-enters to collect jacket. Leaves again at 84 sec
1
Coat-rack Coffee
2 3
4
5
6
12?11?10?9?8
7
Sounder: 4 sec, message: 13s, Total: 17s
Recognition time: time until first movement of
egress behaviour
Response time: time to prepare to leave
Travel time: time to turn to face exit and leave
ROOM
Person Recognition
time (sec)
Response
time (sec)
Travel time
(sec)
Evacuation
time (sec)
1 16 40 5 61
2 15 17 5 37
3 17 20 2 39
4 20 30 3 53
5 16 30 6 52
6 18 39 5 62
7 ? ? 3 67
8 16 30 13 59*
9 ? ? ? 55
10 ? ? ? 65
11 ? ? 2 71
12 ? ? 4 51
Mean 17 29 5 56
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David Purser
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Results
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Results Significant differences between PTAT recognition times and alarm types P< 0.05
Short voice alarm: shortest times, but less reliable response since no one left in Trial 6.
Long voice alarm: slightly longer but most reliable
Sounder: longest and most variable
Recognition time (time to cease normal activity) was main component
With voice alarms occupants tended to wait for message to be repeated before responding
Mean Recognition and Response
times (pooled data)
0
10
20
30
40
50
60
70
Sounder Long short
Time(sec)
Response time
Recognition time
Mean Recognition and Response
times (individual trial data)
0
10
20
30
40
50
60
70
80
T1 T4 T2 T5 T3 T7
Time(sec)
Response time
Recognition time
First and Last Pre-movement
times
0
10
20
30
40
50
60
70
80
Sounder Long short
Time(sec)
Last out
Fiirst out
Message
9 s Message
4 s
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David Purser
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Unnannounced evaucations of BRE buildings - total evacuation times
0
2
4
6
8
10
12
0 0.5 1 1.5 2 2.5 3 3.5
Time (min)
Frequency
For offices and other workplaces with well-trained staff a simple sounder
is sufficient to obtain an efficient evacuation
Office and workshop evacuations
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David Purser
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Design Behavioural Scenarios for Evacuation Time
Quantification
Pre-movement time is often the greater part of evacuation time.
Pre-movement time
? variable, depending on a range of occupant and building systemcharacteristics.
? generally short and predictable when fire safety management cultureand building systems are good, and occupants are alert and welltrained.
? likely to be long and unpredictable otherwise.
Situations differ fundamentally in different types of occupancy
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David Purser
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Sounders, voice alarms and
evacuation management
Simple sounders were found to be effective in buildings with well-trained andwell-managed occupants familiar with the building and systems
Voice alarms were more effective where occupant unfamiliar with the buildingand systems
Reinforcement of evacuation by trained staff found to be very effective in all
cases
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David Purser
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Frequency distribution of pre-movement times
0
2
4
6
8
10
12
00:00 00:20 00:40 01:00 01:20 01:40 02:00
Time (seconds)
Frequency
Most important are the times for the first few people to
move and the last few people to move
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David Purser
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Methods fo r s ingle reta i l enclosu re
For a crowded case - evacuation time for an enclosure (? tevac) is given by:
? tevac = ? tpre(1st percentile) + ? ttrav(walking) + ? ttrav(flow) (1)
? tpre(1st percentile) = time from alarm to movement of first few occupants
? ttrav(walking) = walking time (unimpeded average walking speed x average travel distance to exits).
? ttrav(flow) = time of total occupant population to flow though available exits.
For a sparsely occupied case - Evacuation time from an enclosure is then given by:
? tevac = ? tpre(99th percentile) + ? ttrav(walking) (2)
? tpre(99th percentile) = time from alarm to movement to time of movement of last few occupants
(= time to first percentile plus time from first to 99 th percentile)
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David Purser
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Interactions between pre-travel, presentation and flow times and effects
on evacuation times
Total evacuation time - Sprucefield premovement
0
50
100
150
200
250
300
0 200 400 600 800 1000
Population of space
Time(s)
%95
%99
last out
N & M
%95
%99
Design
populationSprucefield 99% out
%99
presentation
Total evacuation time Sprucefield PTAT distribution
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David Purser
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Effect of fire safety management level on pre-movement time
Persons/sec
Alarm
? tpre(occupant distribution)
Time
Pre-movement time of first occupants to move and
subsequent pre-movement time distribution is lengthened by
progressively lower levels of fire safety management
? tpre(first occupants)
Premovement time distribution - Level M1 managementPre-movement time distribution - Level M2 management
Pre-movement time distribution - Level M3 management
D idP
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David Purser
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Table 2: Suggested pre-times for different design behavioural scenario
categories
Scenario category and modifier ? tpre (first
percentile)
(min)
? tpre (99th percentile)1
(min)
A: awake and familiar:M1 B1 B2 A1 A2
M2 B1 B2 A1 A2M3 B1 B2 A1 A3
For B3 add 0.5 for wayfindingM1 would normally require voicealarm/P.A. if unfamiliar visitors likely tobe present
0.5
1>15
1.0
2>15
B: awake and unfamiliarM1 B1 A1 - A2
M2 B1 A1 A2M3 B1 A1 - A3For B2 add 0.5 for wayfinding
For B3 add 1.0 for wayfindingM1 would normally require voicealarm/P.A
0.5
1.0>15
2
3>15
Ci: sleeping and familiar( e.g. dwellings - individual occupancy)
M2 B1 A1M3 B1 A3For other units in a block assume 1
hourCii: managed occupancy(e.g.serviced apartments, hall of
residence)M1 B2 A1 A2M2 B2 A1 A2M3 B2 A1 A3
Ciii sleeping and unfamiliar(e.g. hotel, boarding house)M1 B2 A1 A2M2 B2 A1 - A2
M3 B2 A1 A3For B3 add 1.0 for wayfindingM1 would normally require voicealarm/P.A.
510
1015
>20
1520
>20
5>20
2025
>20
1520
>20
1total pre-movement time = ? tpre (first percentile) 1st percentile + ? tpre (99th percentile)
Figures with greater levels of uncertainty are italicised
D idP
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David Purser
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Cases where a long period of maintained structural
performance is required
Any sleeping risk (residential domestic, institutional orother [e.g. hotel or HMO]), health care.
Hotels and hostels an immediate simultaneous evacuationstrategy may be used, but long periods are needed and
some occupants may not evacuate. (one hour or more)
Each room or suite needs to be a compartment, at least in
relation to the common escape routes
For apartment blocks of flats or maisonettes the main
strategy is to defend in place. Only the affected unit and
adjacent areas are evacuated. The structure thus needs to withstand burnout of any
particular unit
D idP
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David Purser
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Multi-enclosure multi-storey building case
Floor clearance times for 10-storey two stair office
building:
Modelled in GridFlow
Validation using monitored experimental evacuations
In model and experiments time to clear each floor
very depended upon three parameters:
The maximum specific flow rates (persons/minute/metrewidth) through storey exits, on stairs and through finalexits - range of different values used
The standing capacity on the stair between storeys which for a given stair depends upon the assumed
packing density taken up by the occupants as theydescend the stair limited data available
The merge ratio at the storey exits between occupantson the stair and those from the floor. limited dataavailable
100 stair 0 floor clears from top down
0 stair 100 floor - clears from bottom up
50:50 clears from bottom up
DavidPurser
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David Purser
HER
Representation of stair in Gridflow
Link to floor belowLink to floor above
People descending from floorabove lend to move towards centre
line and slow for the turn
This creates a space for people at
storey exit to merge into the left
hand flow, even under crowded
conditions
The result tends to a 50:50 merge
ratio
Door link formingstorey exit
DavidPurser
Elapsedtimeandnumber
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David Purser
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Gridflow simulation: Simultaneous evacuation of a 10-storeys served two stair building
lobbystair
element Storey andhalf landings
links
Elapsed time and numberof occupants in enclosure
Top
Floor
Occupants descending frommid landing above
Occupants descendingto next mid-landing
DavidPurser Fl d t di it f t i
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David Purser
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Flow and standing capacity of stairs
0
50
100
150
200
250
300
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Time (min)
Occupantnumber
10th floor 9th stair 10th stair 9th floor 8th stair 7th stair 6th stair 5th stair
4th stair 3rd stair 2nd stair 1st stair 9th lobby 10th lobby Final flight 8th floor
8th lobby 7th floor 7th lobby 6th floor 6th lobby 5th floor 5th lobby 4th floor
4th lobby 3rd floor 3rd lobby 2nd floor 2nd lobby 1st floor 1st lobby
9
lobby
8t
lobby
1st
lobby
10t
lobby1st lobby
clears10th lobby
clears
1st lobby
clears8th lobby
clears
9th lobby
clears
9th(fire) floorclearance
Simultaneous evacuation of a 10-storeys served 2
stair building designed for phased evacuation
Maximum stair capacity 66 persons at 4 persons/m2
DavidPurser Times toprotectedstair simultaneous
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David Purser
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Times to protected stair - simultaneousEffect of occupant density on stairs: Default is 4 persons/m2 which is verycrowded, 2 persons/m2 is considered more reasonable and likely.
This increases evacuation times into protected stair
0
1
2
3
4
5
6
7
8
9
0 2 4 6 8 10 12
Floor served
Timetoprotectedstair(min)
10 served 4/m^2
10 served 2/m^2
5 served 2/m^2
5 served 4/m^2
Time for evacuation into a protected stair for two-stair buildings prescriptively designed for simultaneous
evacuation: 5 and 10 storeys served, 2 or 4 persons/m2 maximum occupant density on stair
DavidPurser
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David Purser
HER
Effects of exposure to fire or smoke
Most building occupants will only be aware of alarms and not see smoke
Occupants more likely to start evacuation if more than one cue, sohearing alarms and seeing smoke more effective than alarm alone But occupants underestimate threat from fire and smoke and often go
towards fire to fight it, so being in the same enclosure as the fire doesnot necessarily result in instant evacuation
? Occupants reluctant to enter smoke-logged escape routes, so affectsexit choice
? When exposed to smoke, optical opacity and irritancy slow movementspeed
? Exposure to asphyxiant gases or heat leads to incapacitation when asufficient dose had been inhaled
These effects on evacuation time can be calculated using a combination of evacuation andfractional effective dose modelling
DavidPurser
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David Purser
HER
Conc lus ions
Human behaviour can be adequately incorporated into engineering design by
consideration of a small number of key parameters
Good design with high affordance enables efficient and predictable evacuation
calculations
RSET calculations need to consider detection, alarm, pre-movement andtravel times
Pre movement times most variable but distribution data can be collected for
a simple set of design behavioural scenarios (first and last occupant times the
most important)
Travel times depend mainly on physical parameters, but behavioural aspects
including exit choice, merging behaviours and densities can also be important