purser human fire behaviour 24june09

8/12/2019 Purser Human Fire Behaviour 24June09

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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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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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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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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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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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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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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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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

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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

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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

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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

purser human fire behaviour 24june09

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