Fire Behavior Impact & Safety Tactics | Safety Zone Calculations & Tools

1. Unit 12 – Part 1Gauging Fire Behavior & Guiding Fireline Decisions

2. Unit 12 Objectives • Describe how to apply fire behavior information to safety and suppression decisions. • Demonstrate how to calculate the size of safety zones. • Identify the importance of changes in fire behavior to firefighter safety.

3. 4. Discuss what drives large changes and identify the “next big change.” 5. Demonstrate a simple but systematic method for gauging change and estimating fire spread time. 6. Identify other fire behavior prediction tools. Unit 12 Objectives

4. Fire Behavior Affects Safety and Suppression Decisions

5. Basic Fire Behavior Measures • Flame Length (FL)—a measure of how fast energy is being released at the flaming front. • Rate-of-Spread (ROS)—a measure of how fast the fire front is moving.

6. The distance from the middle of the flaming zone to the average flame tip. Flame Length

7. FlameLength 12-7-S290-EP

8. Applying Flame Length Flame length affects choice of fire suppression tactics and methods. Dictates the dimensions of safe zones.

9. Fire Suppression Limitations Flame Length 0 - 4 ft. 4 - 8 ft. 8 - 11 ft. >11ft. Fires can generally be attacked at the head or flanks by persons using hand tools. Handline should hold the fire. Fires are too intense for direct attack on the head by persons using hand tools. Handline cannot be relied on to hold the fire. Fires may present serious control problems; torching out, crowning and spotting. Control efforts at the head will probably be ineffective. Crowning, spotting and major fire runs are probable. Control efforts at the head of the fire are ineffective.

10. FireCharacteristicsChart(light fuels) 12-10-S290-EP

11. Fire Characteristics Chart(heavy fuels) FIRE BEHAVIOR Fire Characteristics Chart (scale for heavy fuels) 12-11-S290-EP

12. Safety Zone Calculations

13. Definition of a Safety Zone “An area cleared of flammable materials used for escape in the event the line is outflanked or in case a spot fire causes fuels outside the control line to render the line unsafe. They are greatly enlarged areas which can be used with relative safety by firefighters and their equipment in the event of blowup in the vicinity.”

14. Definition of a Deployment Zone “…used when fire conditions are such that escape routes and safety zones have been compromised. Deployment zones are the last ditch areas where fire shelters must be deployed to ensure firefighter survival due to the available space and/or fire behavior conditions at the deployment zone location.”

15. Safety Zone Guidelines • Avoid locations that are: • downwind from fire • in chimneys, saddles, narrow canyons • Take advantage of heat barriers • Burn out safety zones prior to flame front approach

16. Assumptions • Safety Zone size calculations are made on the “worst case scenario.” • All sides of the safety zone will receive the same heat flux. • Based on an crew of 3.

17. x feet x feet Fire and safety zone edge more closely resemble a straight line. Radiant heat transfer from the “sides” is low. Fire surrounding a circular shaped safety zone gives the worst case (most radiant heat transfer).

18. Assumptions Flame Length = Flame Height Safe separation is a straight line from the heat source to the firefighter

19. Flame Height Firefighter Safety Zones Flaming Front Distance Separation Firefighter USDA Forest Service, Fire Behavior Research

20. Safety Zone Equations Flame Height Input: 4 x flame height Consider increasing the distance separation when more than 3 people and 1 engine will occupy the safety zone.

21. Circle Safety Zone-ExampleDistance Separation = the radius of the circle. Flame Height = 20 feet 20’ x 4 = 80’ radius Distance separation = 80 feet Diameter of circle = 80 X 2 = 160’

22. Safety Zone Size Assuming no Slope and no Wind

23. More than 3 people and 1 engine will increase the distance requirement. • Convective heat from wind or terrain will increase the distance separations requirement.

24. Rate of Spread (ROS)Rate of advance of the flame front • Can be given in absolute terms, such as feet-per-minute (ft/min) • Can be given in relative terms, such as twice as fast as before (2X) Spread Time: The time it will take the fire to move a given distance; it can be determined from ROS.

25. Rate of Spread ROS is a keysafety factor …if a fire can catch you it can hurt you!

26. Rate of Spread Changes in ROS are very important to safety and suppression.A universal factor in fireline accidents is a rapid change in ROS.

27. ROS can also be used to express how fire spread rate will change Compare the ROS before with the ROS after a change…how much faster or slower will the fire move? ROS-ratio=(bigger ROS)/(smaller ROS) Example: ROS changes from 10 to 60 (or 60 to 10), ROS-ratio = 60/10 = 6X

28. DIVIDED BY ROS Ratio Example = 6X

29. Rate of Spread Ratio ROS-ratio can indicate the degree of coming danger, and can be used to predict future fire spread time.

30. The “next big change” predict observe project The idea of predicting fire spread in the future, using the “complete application” of FLAME The slope is about as long as the 30-min. spread on the flats. 30 minutes 30 more min. Note: these are ‘spread times’, rather than ‘spread rates’, and are very practical for use on the fireline…how long will it take the fire to go from here to there? If fire moves 3X faster on the slope, it will take 1/3 of 30, or about 10 min. to spread up the slope 12-30-S290-EP

31. What a Change in ROS Can Mean • ROS changes ranging from 60x to 500x have accompanied fireline fatalities. • ROS-ratio of 60x means that fire spread that has taken place over hours can suddenly take place in minutes. • If walking-pace represents “slow” ROS, an increase of 500x would be the equivalent of twice the speed of sound…a huge relative change. • Changes are not instantaneous, and can involve a transition over time (often minutes to 10s of minutes)… But always be aware, change is coming!

32. First Consider “Current” Fire Behavior • Current fire behavior demonstrates the effects of current fuels, terrain and weather, and provides a baseline. • Factors such as live fuel moisture or 10-hour FM do not change rapidly—they are important overall, but vary over longer time scales.

33. Unforeseen Changes Kill Firefighters Rapid, large increase in fire ROS is a common denominator in fatality fires. • ROS increases of 60x and more have been associated with fatality incidents. To be safe requires firefighters: • foresee changes well ahead • have a sense of the size of the change • understand both “current” and “expected” fire behavior

34. Quotes from Fatality-Fire Reports “…benign appearance of fire…no appreciable wind during decision making…” “…burnout was conditioned upon light upslope winds holding…” “Look what it’s doing now.; …the fire didn’t look that bad…” “…assuming they would see the fire coming at the same rate they had all day.” “…intensity and rate-of-spread were much greater than had been anticipated…” “…right flank was backing into a light up-canyon wind. …numerous observers reported that the wind had remained light and steady…” Revealing a reliance on impressions of current behavior, atendency to not foresee the coming dangerous fire behavior.

35. Foreseeing Changes in Fire Behavior

36. It is critical fora firefighter toanticipatethe “next big change” in plenty of time to confront it. Look ahead at the factors that cause big changes.

37. Anticipating the ChangeSupports LCES Lookouts-What to be looking for, and using the most appropriate lookout locations Communications- What key things to communicate and how often Escape routes-Where and how long Safety zones- Close enough and big enough

38. Dominant Change-Makers WIND (effective wind, which includes slope) is the biggest change-maker, ROS changes of 200X or more. FUEL TYPE is a significant contributor to big changes, changes of 15X or more. Grass Litter Crowns (timber & brush) 12-38-S290-EP

39. Another Important Factor 1-hour FM can change fairly rapidly and can cause changes up to 1.6x or so (usually less), but it is a minor change-maker compared to fuel-type or wind. Very important: 1-hour FM is a key factor in the potential for crown fire. 12-39-S290-EP

40. By drawing in the simple pictures both current and expected fire behavior must be consider. If either picture is blank, your evaluation of the fire behavior is incomplete. Typical “Big Change” Events

41. Expected conditions • - Strong winds, • direction change Sudden Wind Change Current conditions - Light winds What are some examples of wind change? 12-41-S290-EP

42. Expected conditions - Crown fire Change in Fuel Type Current conditions - Litter fire 12-42-S290-EP

43. Expected conditions - Downslope litter fire • - Wind-sheltered Slope Reversala major change, often in both fuel and wind Favorable change Current conditions - Upslope crown fire - Wind-exposed 12-43-S290-EP

44. Slope Reversal • Expected conditions - Upslope crown fire • - Wind-exposed Dangerous change Current conditions - Downslope litter fire - Wind-sheltered 12-44-S290-EP

45. Gauging the Changes in Fire Behavior

46. How much does ROS change as fuel factors, wind, and slope change? We’ll look at each factor, to develop our sense of change, and eventually learn to apply guidelines to assess changes in fire behavior.

47. A scaled diagram can help develop a sense of change to expect as conditions change.Specific guidelines will allow us to consider any change in: - fuel type - wind - slope

48. Consider first the effects of changing fine dead fuel moisture (FDFM), a fairly large change, equivalent to a substantial change in relative humidity.Later we’ll introduce a guideline for gauging the effect of FDFM on ROS.

49. FDFM: Timber Litter ROS = 6 ch/h FL = 3 ft. 1-hour fine dead fuel moisture = 2% ROS = 3 ch/h FL = 2 ft. 1-hour fine dead fuel moisture = 10% 12-49-S290-EP

50. FDFM: Logging Slash ROS = 13 ch/h FL = 9 ft. 1-hour fine dead fuel moisture = 2% ROS = 7 ch/h FL = 6 ft. 1-hour fine dead fuel moisture = 10% 12-50-S290-EP