S-190 Intro to Wildland Fire Behavior
Questions and Answers (1-250) – Latest
Update Graded A+
1. A wildland fire is burning on a 60% slope with fuel and weather
identical to flat ground. Which factor best explains the increased rate
of spread uphill?
A) Increased wind speed on the slope
B) The south-facing aspect of the slope
C) Radiant and convective heat from the fire preheating the upslope fuels
D) Gravity pulling flames downward
*C) Radiant and convective heat from the fire preheating the upslope
fuels *
Rationale: On steep slopes, flames are closer to the unburned fuels above,
allowing more efficient preheating by radiation and convection. This
preheating dries and ignites fuels faster, increasing spread rate. Aspect does
not inherently vary with slope steepness, and wind is not necessarily higher .
2. Given a temperature drop from 95°F to 75°F and relative humidity
increase from 10% to 40%, the dead fine fuel moisture (from
laboratory equilibrium) is most likely to:
A) Double
B) Triple
C) Remain the same
D) Decrease by half
*B) Triple *
,Rationale: At 95°F and 10% RH, equilibrium moisture content is
approximately 2-3%. At 75°F and 40% RH, it is approximately 7-8%. This
represents an increase by a factor of about three .
3. A surface fire has a flame length of 5 ft. The canopy base height of
the overstory is 12 ft, with continuous ladder fuels. Which statement
best describes the expected fire behavior?
A) No crown fire activity is possible
B) Active crown fire is imminent
C) Passive crown fire may occur
D) The fire will remain a surface fire only
*C) Passive crown fire may occur *
Rationale: According to Van Wagner's crown fire initiation model, when
flame length exceeds one-third of the canopy base height, passive crown fire
is possible. Here, 5 ft > 4 ft (1/3 of 12 ft), so passive torching may occur, but
not active crown fire because flame length does not exceed the full canopy
base height .
4. Spotting is most likely to occur when:
A) Relative humidity is high
B) Wind speed exceeds the critical threshold for firebrand lofting
C) Temperature is low
D) The atmosphere is stable
*B) Wind speed exceeds the critical threshold for firebrand lofting *
Rationale: Spotting requires firebrands to be lofted and carried by wind. If
wind speed is below the threshold needed to lift and transport firebrands,
,spotting distances are minimal. High humidity and stable conditions reduce
fire activity, making spotting less likely .
5. According to safety zone guidelines, if the predicted flame length is
20 ft, what is the minimum recommended radius of a safety zone?
A) 40 ft
B) 60 ft
C) 80 ft
D) 100 ft
*C) 80 ft *
Rationale: The standard safety zone size guideline is a radius equal to at least
four times the expected flame length. For 20 ft flames, this gives 80 ft. While
many agencies adopt a minimum of 100 ft, the 4x rule is the basic principle
taught in S-190 .
6. Which of the following fuel models would have the highest Energy
Release Component (ERC) under dry conditions?
A) Grass (FM1)
B) Brush (FM4)
C) Timber litter (FM9)
D) Slash (FM11)
*D) Slash (FM11) *
Rationale: ERC correlates with total available fuel loading. Slash fuel models
contain high fuel loads from logging debris, leading to large potential heat
release per unit area. Grass, timber, and brush have lower fuel loads and thus
lower ERC values under similar dry conditions .
, 7. A fuel particle with a diameter of 0.5 inches is classified as a 10-hour
timelag fuel. After a precipitation event, the fine fuel moisture content
rises to 25%. Which fire behavior characteristic is MOST critical for this
fuel at that moisture level?
A) The fuel will ignite readily
B) The fuel will not support combustion until it dries below 15% moisture
C) The fuel will burn with high intensity
D) The fuel moisture has no effect on combustion
*B) The fuel will not support combustion until it dries below 15%
moisture *
Rationale: At 25% moisture, 10-hour timelag fuels (0.25-1 inch diameter) are
above the moisture of extinction (typically 20-25% for these fuels), so they
will not support flame combustion. The large particle size and high moisture
prevent ignition .
8. During a low-intensity surface fire in heavy timber, a firefighter
observes distinct firebrands being lofted and carried downwind,
igniting new fires. Which combination of conditions would MOST
increase the spotting distance for these firebrands?
A) High relative humidity and stable atmosphere
B) Low relative humidity, moderate winds, and a dry, unstable atmosphere
C) Calm winds and cool temperatures
D) High moisture content in firebrands
*B) Low relative humidity, moderate winds, and a dry, unstable
atmosphere *
Rationale: Spotting distance is increased by strong updrafts (from convection)
that lift firebrands high, and by winds aloft that carry them farther. Low
Questions and Answers (1-250) – Latest
Update Graded A+
1. A wildland fire is burning on a 60% slope with fuel and weather
identical to flat ground. Which factor best explains the increased rate
of spread uphill?
A) Increased wind speed on the slope
B) The south-facing aspect of the slope
C) Radiant and convective heat from the fire preheating the upslope fuels
D) Gravity pulling flames downward
*C) Radiant and convective heat from the fire preheating the upslope
fuels *
Rationale: On steep slopes, flames are closer to the unburned fuels above,
allowing more efficient preheating by radiation and convection. This
preheating dries and ignites fuels faster, increasing spread rate. Aspect does
not inherently vary with slope steepness, and wind is not necessarily higher .
2. Given a temperature drop from 95°F to 75°F and relative humidity
increase from 10% to 40%, the dead fine fuel moisture (from
laboratory equilibrium) is most likely to:
A) Double
B) Triple
C) Remain the same
D) Decrease by half
*B) Triple *
,Rationale: At 95°F and 10% RH, equilibrium moisture content is
approximately 2-3%. At 75°F and 40% RH, it is approximately 7-8%. This
represents an increase by a factor of about three .
3. A surface fire has a flame length of 5 ft. The canopy base height of
the overstory is 12 ft, with continuous ladder fuels. Which statement
best describes the expected fire behavior?
A) No crown fire activity is possible
B) Active crown fire is imminent
C) Passive crown fire may occur
D) The fire will remain a surface fire only
*C) Passive crown fire may occur *
Rationale: According to Van Wagner's crown fire initiation model, when
flame length exceeds one-third of the canopy base height, passive crown fire
is possible. Here, 5 ft > 4 ft (1/3 of 12 ft), so passive torching may occur, but
not active crown fire because flame length does not exceed the full canopy
base height .
4. Spotting is most likely to occur when:
A) Relative humidity is high
B) Wind speed exceeds the critical threshold for firebrand lofting
C) Temperature is low
D) The atmosphere is stable
*B) Wind speed exceeds the critical threshold for firebrand lofting *
Rationale: Spotting requires firebrands to be lofted and carried by wind. If
wind speed is below the threshold needed to lift and transport firebrands,
,spotting distances are minimal. High humidity and stable conditions reduce
fire activity, making spotting less likely .
5. According to safety zone guidelines, if the predicted flame length is
20 ft, what is the minimum recommended radius of a safety zone?
A) 40 ft
B) 60 ft
C) 80 ft
D) 100 ft
*C) 80 ft *
Rationale: The standard safety zone size guideline is a radius equal to at least
four times the expected flame length. For 20 ft flames, this gives 80 ft. While
many agencies adopt a minimum of 100 ft, the 4x rule is the basic principle
taught in S-190 .
6. Which of the following fuel models would have the highest Energy
Release Component (ERC) under dry conditions?
A) Grass (FM1)
B) Brush (FM4)
C) Timber litter (FM9)
D) Slash (FM11)
*D) Slash (FM11) *
Rationale: ERC correlates with total available fuel loading. Slash fuel models
contain high fuel loads from logging debris, leading to large potential heat
release per unit area. Grass, timber, and brush have lower fuel loads and thus
lower ERC values under similar dry conditions .
, 7. A fuel particle with a diameter of 0.5 inches is classified as a 10-hour
timelag fuel. After a precipitation event, the fine fuel moisture content
rises to 25%. Which fire behavior characteristic is MOST critical for this
fuel at that moisture level?
A) The fuel will ignite readily
B) The fuel will not support combustion until it dries below 15% moisture
C) The fuel will burn with high intensity
D) The fuel moisture has no effect on combustion
*B) The fuel will not support combustion until it dries below 15%
moisture *
Rationale: At 25% moisture, 10-hour timelag fuels (0.25-1 inch diameter) are
above the moisture of extinction (typically 20-25% for these fuels), so they
will not support flame combustion. The large particle size and high moisture
prevent ignition .
8. During a low-intensity surface fire in heavy timber, a firefighter
observes distinct firebrands being lofted and carried downwind,
igniting new fires. Which combination of conditions would MOST
increase the spotting distance for these firebrands?
A) High relative humidity and stable atmosphere
B) Low relative humidity, moderate winds, and a dry, unstable atmosphere
C) Calm winds and cool temperatures
D) High moisture content in firebrands
*B) Low relative humidity, moderate winds, and a dry, unstable
atmosphere *
Rationale: Spotting distance is increased by strong updrafts (from convection)
that lift firebrands high, and by winds aloft that carry them farther. Low
