CBM Smoke Management & Post-Burn Evaluation 2 — Questions and Answers
Question 1: Which atmospheric condition creates the greatest risk of smoke intrusion into valley communities during a prescribed burn?
- Strong afternoon sea breeze
- Stable nocturnal inversion layer (Correct answer)
- High mixing height above 5,000 feet
- Gusty synoptic-scale winds
Correct answer: Stable nocturnal inversion layer
A stable nocturnal inversion traps smoke near the surface, preventing vertical mixing and allowing smoke to flow downslope into communities.
Question 2: Under the USDA Smoke Management Guidelines, what is the primary purpose of calculating a Ventilation Index (VI)?
- Estimating the total tonnage of smoke produced per acre
- Determining the potential for smoke dispersal based on mixing height and transport wind speed (Correct answer)
- Predicting ignition probability on a given burn day
- Measuring PM2.5 concentrations at receptor sites
Correct answer: Determining the potential for smoke dispersal based on mixing height and transport wind speed
The Ventilation Index combines mixing height and transport wind speed to quantify the atmosphere's ability to dilute and carry away smoke.
Question 3: A burn manager observes that smoke is lying flat and drifting slowly along the ground after ignition. This condition most likely indicates:
- Convective activity is sufficient for good smoke lift
- The atmosphere is in a stable state with poor vertical mixing (Correct answer)
- Transport winds are adequate to clear smoke from the burn unit
- Fuel moisture content is too high to sustain combustion
Correct answer: The atmosphere is in a stable state with poor vertical mixing
Flat, ground-hugging smoke plumes are a visual indicator of atmospheric stability and insufficient convective mixing height.
Question 4: Which post-burn assessment metric best indicates whether fire achieved the desired understory fuel reduction objective?
- Percentage of tree canopy scorched
- Depth of char on standing snags
- Percent consumption of fine woody debris and litter layer (Correct answer)
- Number of residual fire spots per acre
Correct answer: Percent consumption of fine woody debris and litter layer
Fine woody debris and litter consumption percentage directly measures how thoroughly surface fuels were reduced, which is the primary hazard reduction goal.
Question 5: When documenting post-burn effects for an agency record, which of the following best describes an appropriate method for estimating burn severity?
- Recording the perimeter length of the blackened area
- Using the Composite Burn Index (CBI) at systematically placed field plots (Correct answer)
- Counting the number of trees killed within the unit
- Measuring the average flame length reported during ignition
Correct answer: Using the Composite Burn Index (CBI) at systematically placed field plots
The Composite Burn Index provides a standardized, multi-strata field assessment of burn severity across overstory, understory, and soil layers.
Question 6: A prescribed burn in the southeastern US produces a large smoke column that reaches the mixing height. The most immediate air quality concern is:
- Ground-level ozone accumulation at night
- Long-range transport of PM2.5 to distant Class I airsheds (Correct answer)
- Carbon monoxide buildup inside the burn unit
- Acid rain formation downwind of the burn
Correct answer: Long-range transport of PM2.5 to distant Class I airsheds
When smoke reaches the mixing height, it can be transported horizontally over long distances, potentially impacting Class I wilderness areas with PM2.5.
Question 7: Which burn-day forecast product should a burn manager consult to estimate the height above ground at which smoke will mix and disperse?
- Haines Index forecast
- Mixing height forecast from NOAA/NWS spot weather (Correct answer)
- Keetch-Byram Drought Index map
- Fine Fuel Moisture Code reading
Correct answer: Mixing height forecast from NOAA/NWS spot weather
The NWS spot weather forecast provides site-specific mixing height predictions, which are essential for evaluating smoke dispersal potential.
CBM Smoke Management & Post-Burn Evaluation 2
Which atmospheric condition creates the greatest risk of smoke intrusion into valley communities during a prescribed burn?