fire behaviour and firefighter safety -...

AF3 Conference & Summer School on Forest Fire Management, Istituto Superiore Antincendi, Rome, Italy, Sept. 20-22, 2016

Fire behaviour

and firefighter

safety

Paulo Fernandes

Outline

1. Introduction: fire behaviour

2. Fire behaviour, extinction capacity and safety

3. Fire behaviour analysis for effective and safe fire suppression

4. Fire safety, the fire environment, and suppression operations

5. Conclusion

Fire behaviour – what’s the fire doing? – fundamentally defines a

wildland fire

• Movement (horizontal and vertical spread)

• Fuel consumption

• Heat energy production through visible flaming combustion

Fire behaviour interpretation and applications:

Fuel management, fire danger, fire preparedness, fire suppression and

safety, fire effects

Fuel

Introduction: fire behaviour


“Every fire behavior situation calls for specific safety measures.

Experience gained from fighting thousands of fires has shown that the

suppression job may be accomplished with a reasonable degree of

safety. To achieve safety it is highly important that all firefighters have

a general knowledge and the leaders of the firefighting forces have a

high degree of knowledge of fire behavior. … Many risks can be

eliminated from firefighting if each man knows what to expect the fire

to do.”

In: Fire Behavior in Northern Rocky Mountain Forests (Barrows, 1951)

Fire suppression is implicitly dangerous.

Firefighter safety relies on understanding

fire behaviour.


Fire behavior characteristics

relevant for fire suppression

operations:

• Type of fire

• Rate of Spread

• Rates of perimeter and area

increase

• Fireline intensity

• Flame dimensions

• Spotting density and distance

• Fire size and shape

• Residence time and burn-out

time


Fire behaviour prediction is a systematic process that

blends science and art

Barrows (1951)

Fireline intensity

• Varies in the range of 10 – 100 000 kW/m

• Determines extinction capacity, i.e. the

effectiveness of fire control

I = H x W x R

Fireline

intensity

(kW/m)

Fuel consumed

(kg/m2)

Rate of fire

spread (m/s)

Heat of

combustion

(kJ/kg)

Fire behaviour, extinction capacity and safety

Fire control effectiveness as

a function of fireline intensity


Fire control effectiveness as

a function of flame length

Hirsch & Martell (1996), Int. J. Wildland Fire 6: 199-215

Litter+shrubs (18.0 t/ha)

fine dead fuel moist. cont. = 4%

Litter+shrubs (18.0 t/ha)

fine dead fuel moist. cont. = 12%

Litter (8.5 t/ha), fine dead fuel

moist. cont. = 4%

Litter (8.5 t/ha), fine dead fuel

moist. cont. = 12%

Surface fire behaviour and difficulty of control in

Pinus pinaster stands


Crowning

transition

Limit of effective control by direct attack

Fire control effectiveness as a function of

fire danger rating


FWI-based fire danger rating classes based

on extinction capacity

Palheiro et al. (2006), 5th ICFFR

Fire Danger Rating

(Canadian FWI System)

21 September 2016

EFFIS - European Forest Fire

Information System

http://forest.jrc.ec.europa.eu/effis/

Past wildfires >2500 ha

2016 large wildfires

Fire danger rating,

extinction capacity

and large fire

activity in Portugal

Fir

e b

eh

av

iou

r, e

xti

ncti

on

cap

acit

y a

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safe

ty


Coping with the limits to fire control

Monchique, Portugal, September 2016

Direct attack

Hand tools

Water tankers

Direct attack

Hand tools

Water tankers

Direct attack

Water tankers

Aircraft

Parallel and indirect attack

Direct attack

Water tankers

Aircraft


Direct attack

Water tankers

Aircraft


Fire behaviour

analysis for

effective and safe

fire suppression

operations


“We consider certain types of fire behavior unusual or

unexpected only because we have failed to evaluate

properly the conditions, influences, and forces that are

in control”

Countryman (1972)

Fire behaviour analysis for effective and safe fire suppression

Fatalities and injuries in firefighting operations are often

directly related with the inability to assess and anticipate

changes in the fire environment and its consequences


sept. 6, morning

sept. 6, afternoon sept. 7, afternoon

Example of a common situation and potential safety risk:

A cold front changes wind direction and speed: flank fires become head fires

Extreme fire danger

FWI >50


When wind direction

changes: the Dead-Man Zone

• Firefighters working in parallel or

indirect attack

• The line of fire will immediately

attain its potential rate of spread

• Firefighters will have very little

time to reach a safe area


When wind direction changes: the Dead-Man Zone

Burn over by the fireBurn over by the

counter-fire

Change in wind + slope

Burn over by the fire

Role of the fire behaviour analyst

Predict fire behaviour in a timely manner

• Using data from different sources

• Current and forecasted weather

• Local fuel and terrain conditions

• Observed fire behaviour

Using standard systems

• Predictions comparable between individuals

and situations

• Documentation available

• Useful for training

Main results:

• Identification of potential safety problems

Threats to human life and property

Unsafe locations for firefighting

• Predicted fire growth map

• Potential fire threat and impact

• Documentation

• Fire suppression potential


Basic fire behaviour analysis with the CPS system

Objectives:

• To rapidly assess potential changes

• To anticipate danger and opportunities for effective control

• To fight fire safely and only where success is warranted


Firefighting tactics defined by fire type and relative alignment:

Wind-driven: Direct or parallel attack on flanks

Convective (fuel-driven) Indirect attack

Topographic Window of opportunity

Extreme fire environment Withdraw (defensive)

The CPS logic: “alignment of forces”

• Wind, slope, and aspect (effect on fuel temperature/moisture)

• The alignment and strength of forces in the fire’s path is assessed

• Fire intensity will increase/decrease where these forces are

more/less aligned, hindering/allowing fire control


Cramer fire (2003, U.S.) fatalities:

Tactical failure under full alignment of forces

Fire safety, the fire environment, and suppression operations

Extreme fire behaviour is inherently dangerous for firefighters

and usually impedes direct action on the fire:

• Fast fire spread and high fire intensity

• Crown fire activity

• Abundant spotting

• Large fire whirls

• Well-developed convection column

• Strong response to changes in wind

and slope when fine dead fuels

become increasingly drier

ISI 33

• Blow-up potential increases as

medium and heavy dead fuels

and live fuels decrease in

moisture content


Drier fuels make fire behaviour more unstable and extreme

ISI 33


What is common to fire behaviour on tragedy

and near-miss fires?

• Small fires and isolated sections of large fires account

for most incidents: underestimation

• Fuel loads are apparently low: more relevant role of

other factors

• Most fires appear inoffensive until winds shift in

direction and/or velocity: the fire environment favours

changes; alignment of factors

• Incidents can happen in the mop-up stage:

complacency

• Unexpected fast fire spread in canyons, narrow

valleys and steep terrain: underestimation; alignment

of factors

ISI 33


*Additional near-miss incident factors:

• Poor weather forecasting

• Poor interpretation of weather and fire danger rating in terms of

potential fire behaviour

• Attack strategies disregarding potential fire behaviour

• Non-defined escape routes

• Poor communication

* Safety review team report - a summary of the 1994 fire season. British Columbia Forest Service.


• Narrow valleys are

easily crossed by fire

• Spot fires drawn to

the main fire

• Fire whirls often form on the

leeward side of a ridge

• Wind channeling

in canyons

• Slope reversal

Puerto Madryn, Argentina, Jan. 21, 1994: 25 fatalities

“The initial assessment made by

the crew leader was that the fire

was small and easy to control”

Logistics officer statement:

“I perceived a sudden calm, saw

the flames rising and forming like

a flame wall. Then I heard an

extremely loud sound and

perceived a sudden increase in

fire activity”


Most injuries and fatalities result

from temporary and often sudden

increases in fire behaviour activity

Dentoni et al. (2001), Meteorological

Applications 8: 361–370

Cause:

Change in synoptic condition +

daily wind cycle (sea breeze)


Provisions for firefighter safety

• Ten Standard Firefighting Orders

• Eighteen “Watch Out!” Situations

• LACES Wildland Fire Safety System

• Margin of Safety concept

• Safety distances

• The Dead-Man Zone


Gleason (1991), Fire Management Notes 52: 9

LACES Wildland Fire Safety System

• Lookout(s)

• Anchor point(s)

• Communication(s)

• Escape routes

• Safety zone(s)


Alexander et al. (2015)

Useful, but usually difficult

to apply in practice …

“Margin of Safety” concept

Safety Margin = T1 – T2

T1 = time for the fire to reach

the safety zone (SZ)

T2 = time for the firefighter (FF)

to reach the safety zone (SZ)

Beighley (1995)

Distance travelled versus time since the decision of using an escape route

for various scenarios

Alexander et al. (2005), In: 8th Int. Wildland Fire Safety Summit



Butler & Cohen (1998), Int. J. Wildland Fire 8: 73-77

Safety distance to fire

Radiant heat flux as a function of flame height

and distance from the flame

* Safety Distance =

4 x Flame Height

* For firefighters wearing protective

(Nomex) clothing


Safety distance to fire (Zarate et al. 2008, Fire Safety Journal 43: 565-575)

Wind>30 km/hr, slope>30%

Wind>30 km/hr, slope=20%

or wind = 15-30 km/hr, slope>30%

Wind>30 km/hr, flat terrain

or wind = 15-30 km/hr, slope=20%

or wind = 0-15 km/hr, slope>30%

Wind=16-30 km/hr, flat terrain

or wind = 0-15 km/hr, slope=20%

Wind=0-10 km/hr, flat terrain

Vegetation height (m)

Sa

fety

dis

tan

ce

(m

)


Wind>30 km/hr, flat terrain

or wind = 15-30 km/h, slope=20%

or wind = 0-15 km/h, slope>30%

Safety distance to fire

Radiation and convection, flame height replaced by vegetation height


Firefighters safety in relation to suppression fire


Much can be learned by analysing

incidents

Conclusion

• Firefighting is reasonably safe provided that fire behaviour is properly

understood and anticipated.

• Safe firefighting practices should recognize and integrate the natural limits

for effective fire control operations.

• Fire behaviour analysis is crucial for effective and safe firefighting.

• Most injuries and fatalities during fire control operations are a

consequence of not appreciating changes in the fire environment. Such

alterations can be sudden and modify fire intensity from low to extreme.

• Operational guidelines for safe firefighting, including of quantitative nature,

are well developed.

fire behaviour and firefighter safety -...

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