Upload
vokhanh
View
218
Download
0
Embed Size (px)
Citation preview
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
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.
Introduction: 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
Introduction: fire behaviour
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 behaviour, extinction capacity and safety
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
Fire behaviour, extinction capacity and safety
Crowning
transition
Limit of effective control by direct attack
Fire control effectiveness as a function of
fire danger rating
Fire behaviour, extinction capacity and safety
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
nd
safe
ty
Fire behaviour, extinction capacity and safety
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
Parallel and indirect attack
Direct attack
Water tankers
Aircraft
Parallel and indirect attack
Fire behaviour
analysis for
effective and safe
fire suppression
operations
Fire behaviour, extinction capacity and safety
“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
Fire behaviour analysis for effective and safe fire suppression
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
Fire behaviour analysis for effective and safe fire suppression
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
Fire behaviour analysis for effective and safe fire suppression
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
Fire behaviour analysis for effective and safe fire suppression
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
Fire behaviour analysis for effective and safe fire suppression
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
Fire behaviour analysis for effective and safe fire suppression
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
Fire safety, the fire environment, and suppression operations
Drier fuels make fire behaviour more unstable and extreme
ISI 33
Fire safety, the fire environment, and suppression operations
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
Fire safety, the fire environment, and suppression operations
*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.
Fire safety, the fire environment, and suppression operations
• 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”
Fire safety, the fire environment, and suppression operations
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)
Fire safety, the fire environment, and suppression operations
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
Fire safety, the fire environment, and suppression operations
Gleason (1991), Fire Management Notes 52: 9
LACES Wildland Fire Safety System
• Lookout(s)
• Anchor point(s)
• Communication(s)
• Escape routes
• Safety zone(s)
Fire safety, the fire environment, and suppression operations
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
Fire safety, the fire environment, and suppression operations
Fire safety, the fire environment, and suppression operations
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
Fire safety, the fire environment, and suppression operations
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
)
Fire safety, the fire environment, and suppression operations
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
Fire safety, the fire environment, and suppression operations
Firefighters safety in relation to suppression fire
Fire safety, the fire environment, and suppression operations
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.