S-130 Fire Behavior & Weather 2 — Questions and Answers
Question 1: Which atmospheric condition causes a temperature inversion and what effect does it have on wildland fire behavior?
- Warm air trapped beneath a layer of cooler air, suppressing smoke and reducing fire spread
- A layer of warm air above cooler surface air, which traps smoke and limits vertical mixing (Correct answer)
- Cool air aloft pushing down on warm surface air, increasing wind speed at ground level
- Equal temperature at all altitudes, promoting uniform fire spread in all directions
Correct answer: A layer of warm air above cooler surface air, which traps smoke and limits vertical mixing
A temperature inversion occurs when warm air sits above cooler surface air, trapping smoke and moisture near the ground and generally reducing fire activity.
Question 2: What does the term 'fire whirl' refer to in wildland firefighting?
- A circular burn pattern left after a fire passes through an area
- A spinning vortex of fire and hot gases that can hurl burning debris great distances (Correct answer)
- The circular path a helicopter takes when water-dropping on a fire
- A weather pattern that causes fires to rotate around a central high-pressure area
Correct answer: A spinning vortex of fire and hot gases that can hurl burning debris great distances
A fire whirl is a rotating column of fire and hot gases that can spread embers far ahead of the main fire front and is extremely dangerous to firefighters.
Question 3: How does relative humidity below 25% affect wildland fire danger?
- It has minimal effect because moisture in live fuels remains constant regardless of humidity
- It significantly increases fire danger by drying fine fuels and promoting rapid ignition and spread (Correct answer)
- It reduces fire danger because dry air produces less oxygen for combustion
- It only affects fire behavior in coastal regions where sea breezes are common
Correct answer: It significantly increases fire danger by drying fine fuels and promoting rapid ignition and spread
Relative humidity below 25% dries fine fuels rapidly, lowering their moisture content and dramatically increasing the likelihood of ignition and fast fire spread.
Question 4: What is the 'aspect' of a slope and why does it matter in predicting fire behavior?
- The steepness angle of the slope, which determines how fast fire climbs uphill
- The compass direction a slope faces, which affects fuel moisture and fire intensity (Correct answer)
- The length of the slope from base to ridge, which influences spotting distance
- The type of vegetation on a slope, which determines fuel load and fire spread rate
Correct answer: The compass direction a slope faces, which affects fuel moisture and fire intensity
Aspect refers to the compass direction a slope faces; south- and west-facing slopes receive more direct sunlight, drying fuels more and producing more intense fire behavior.
Question 5: During an approaching cold front, what fire behavior change should a firefighter anticipate?
- Gradual decrease in wind speed followed by steady rain that extinguishes the fire
- Sudden wind shift and increase in wind speed that can cause the fire to spread rapidly in a new direction (Correct answer)
- Slow increase in relative humidity that steadily reduces fire intensity over several hours
- A drop in temperature that causes fuels to absorb moisture and self-extinguish
Correct answer: Sudden wind shift and increase in wind speed that can cause the fire to spread rapidly in a new direction
Cold fronts are associated with sudden wind shifts and gusts that can rapidly change a fire's direction and intensity, creating extremely dangerous conditions for firefighters.
Question 6: Which type of fuel moisture is most critical to monitor for predicting fire ignition potential?
- Moisture content of 1,000-hour fuels such as large logs and heavy timber
- Moisture content of 1-hour fuels such as fine grasses, pine needles, and small twigs (Correct answer)
- Moisture content of live shrubs and green grasses
- Moisture content of the duff layer beneath the surface litter
Correct answer: Moisture content of 1-hour fuels such as fine grasses, pine needles, and small twigs
One-hour fuels (fine grasses, needles, small twigs) respond quickly to atmospheric conditions and are the primary carriers of fire ignition and initial spread.
Question 7: What is a 'spot fire' and why is it particularly dangerous on the fireline?
- A small prescribed burn used to reduce fuel loads ahead of a wildfire
- A fire started by embers carried ahead of the main fire front, potentially trapping firefighters (Correct answer)
- A designated safe zone marked with colored flags for firefighters to retreat to
- A localized hot spot within the black (burned) area that can reignite
Correct answer: A fire started by embers carried ahead of the main fire front, potentially trapping firefighters
Spot fires are ignited by firebrands (burning embers) transported by wind ahead of the main fire, and can quickly grow to surround and trap firefighters who are unaware of them.
S-130 Fire Behavior & Weather 2
Which atmospheric condition causes a temperature inversion and what effect does it have on wildland fire behavior?