5.3 Spread Distance |

## Spread DistanceSpread distance (SD) is the forward distance a fire spreads in a given amount of time. SD can be calculated from rate of spread (ROS) and projected time (PT). ## Map spread worksheetThese values can be summarized in a Map Spread Worksheet.
Map Spread Worksheet (completed)
When completing the map spread worksheet, notice that the projection point is line zero. Line 1 begins with the rate of spread. Fire Area Size Worksheet
## Practice
1. Do I have the information I need to fill out a map spread worksheet? The correct answer is a, yes. If you know the rate of spread, projection time, and map scale, you can fill out a map spread worksheet. 2. What is the rate of spread? The rate of spread is 12 chains/hr. 3. What is the projection time? The projection time is 3 hours. 4. What is the spread distance in chains? The correct answer is d, 36 chains. SD = ROS × PT = 12 × 3 = 36. 5. What is the spread distance in feet? 36 chains × 66 ft/chain = 2376 ft. 6. What is the map scale (in/in)? The correct answer is a, 1:21,120. 7. What is the conversion factor to ft/in? The correct answer is c, 1760 ft/in. 8. What is the map spread distance? The correct answer is 1.35 in. A ground distance of 2376 ft translates to 1.35 in on this map. ## Forward Rate of SpreadThe shape of a fire is dependent on slope and effective windspeed. The higher the windspeed and slope percent, the longer, more cigar-shaped the burn area. Safety dictates that firefighters be positioned at the flanks (sides) or back of a fire. A firefighter should never be uphill (at the head) of a fire where the rate of spread is the fastest. See the Standard Fire Orders (F-I-R-E-O-R-D-E-R-S) in the Fireline Handbook, PMS 410-1 or NFES 0065. ## Using a Scaled Ruler for Spread MeasurementsWhen drawing or measuring distances, a scaled ruler is sometimes necessary for direct measurements. A scaled ruler, or engineer's ruler, has 1-inch increments subdivided into 1/10-inch increments, convenient for ground measurements. Ground measurements are usually given in fractions of multiples of 10. Consider a map distance of 3.7 inches, where 1 inch equals 100 feet. In this case, each tenth of an inch will equal 10 feet. Consequently, 3.7 inches equals 370 feet. ## Map Spread WorksheetAll data collected and calculated related to spread distance and rate of spread can be put into a map spread worksheet. |