S-130 Fire Behavior & Weather 3 — Questions and Answers
Question 1: What is the primary cause of the 'afternoon peak' in fire danger that typically occurs between 2:00 PM and 4:00 PM?
- Increased human activity during daylight hours raises the probability of ignition
- Maximum temperature combined with minimum relative humidity creates the most critical fire weather conditions (Correct answer)
- Wind speeds are always highest in the mid-afternoon due to pressure gradients
- Fuel moisture in large logs reaches its daily minimum in the mid-afternoon
Correct answer: Maximum temperature combined with minimum relative humidity creates the most critical fire weather conditions
The afternoon peak in fire danger results from daily maximum temperatures and minimum relative humidity occurring simultaneously, creating the driest and most ignition-prone conditions.
Question 2: How do 'fuels' in the context of the fire triangle contribute to fire behavior intensity?
- Fuels only determine where a fire starts, not how intensely it burns once ignited
- The quantity, arrangement, moisture content, and type of fuels all directly influence fire intensity and rate of spread (Correct answer)
- Only the total weight of fuels matters; arrangement and moisture content are secondary factors
- Live fuels never contribute to fire intensity because their high moisture content prevents combustion
Correct answer: The quantity, arrangement, moisture content, and type of fuels all directly influence fire intensity and rate of spread
Fuel characteristics including quantity, continuity, moisture content, size, and arrangement collectively determine how much energy a fire releases and how fast it spreads.
Question 3: What phenomenon causes fires to burn more intensely and spread faster on steep slopes?
- Gravity causes burning material to roll downhill, igniting new fuels below the fire
- Slope preheats uphill fuels through convective and radiant heat, and chimney effect accelerates uphill spread (Correct answer)
- Cool air at higher elevations causes fires to burn hotter to maintain combustion temperature
- Steep slopes always have drier fuels due to faster water runoff after precipitation
Correct answer: Slope preheats uphill fuels through convective and radiant heat, and chimney effect accelerates uphill spread
On steep slopes, heat rises and preheats fuels above the fire, and the chimney effect channels hot gases uphill, dramatically accelerating the rate of spread up the slope.
Question 4: What is 'crowning' in wildland fire behavior?
- The practice of posting lookouts on hilltops to monitor fire spread
- Fire that moves through the tops of trees independently of or in conjunction with surface fire (Correct answer)
- The formation of a rounded smoke column that indicates stable atmospheric conditions
- Burning material that falls from tree canopies onto the ground surface
Correct answer: Fire that moves through the tops of trees independently of or in conjunction with surface fire
Crowning occurs when fire moves through the tree canopy and can be passive (dependent on surface fire) or active (self-sustaining), and is associated with extreme rates of spread.
Question 5: Which wind pattern is most commonly associated with dangerous Foehn (downslope) winds in the western United States?
- Moist onshore flow from the Pacific Ocean that compresses as it descends mountains
- Dry, warm air that compresses and heats as it descends the leeward side of a mountain range (Correct answer)
- Cool night air that drains downhill into valleys, increasing relative humidity
- Strong upper-level jet stream winds that funnel through mountain passes at ground level
Correct answer: Dry, warm air that compresses and heats as it descends the leeward side of a mountain range
Foehn winds (called Santa Ana in Southern California) are dry, warm winds created when air descends and compresses on the leeward side of mountains, dramatically reducing humidity and increasing fire danger.
Question 6: In the context of wildland fire, what does 'backing fire' mean?
- A fire that has been purposely set to burn back toward the main fire to create a fuel break
- A fire spreading into the wind or downhill, moving slowly with lower intensity (Correct answer)
- A fire behavior where the main flame front reverses direction due to a wind shift
- Firefighters retreating to a safety zone while the fire advances toward their position
Correct answer: A fire spreading into the wind or downhill, moving slowly with lower intensity
A backing fire spreads against the wind or downhill, resulting in slower spread rates, lower flame lengths, and generally lower intensity than head fire or flanking fire.
Question 7: What is the significance of 'critical fire weather' as defined in S-130 training?
- Any weather condition that causes a fire to exceed the initial attack capability of available resources
- A combination of low humidity, high temperature, and strong winds that dramatically increases fire danger (Correct answer)
- Weather conditions that make aerial firefighting operations unsafe due to turbulence or visibility
- Thunderstorm activity that increases lightning ignition risk without providing significant rainfall
Correct answer: A combination of low humidity, high temperature, and strong winds that dramatically increases fire danger
Critical fire weather refers to the combination of low relative humidity (typically below 25%), high temperatures, and strong or erratic winds that create extreme fire behavior potential.
S-130 Fire Behavior & Weather 3
What is the primary cause of the 'afternoon peak' in fire danger that typically occurs between 2:00 PM and 4:00 PM?