Accuracy is a gauge of how close the measured value is to the true value. The accuracy of a measurement refers to the number of significant digits. See Section 1.6.

Example 1 - Gabe is measuring a length of connector hose. He measures it three times. The values he gets are 2.1 feet, 2.2 feet, and 2.2 feet. The actual value is 2.15 feet. How accurate are Gabe's three measured values?

Step 1. The accuracy of the measurements is the difference between the true value and the measured value.
2.15 - 2.1 = 0.05

Step 2. Repeat the same process for the other measurements.
2.15 - 2.2 = - 0.05

The accuracy of the measurement is ± 0.05 feet. 

Precision is an indicator of how close the repeated measurements are to each other. The precision of a measurement refers to the smallest unit with which a measurement can be made.

Example 1 - Find the precision of Gabe's measured the length of hose connector: 2.1 ft, 2.2 ft, and 2.2 ft.

Step 1. Subtract the measurements from each other.
2.1 - 2.2 = -0.1

The precision of the measurement is ±0.1 feet.

The average, or the mean, is the sum of all the numbers divided by the number of terms.

Example 1 - The line production rates for the members of a hand crew were as follows: 8.0 chains per hour, 7.0 chains per hour, 6.0 chains per hour, 7.5 chains per hour, and 7.0 chains per hour. What is the average number of fireline chains constructed per hour?

Step 1. Add all the numbers.
8.0 + 7.0 + 6.0 + 7.5 + 7.0 = 35.5 chains

Step 2. Count the number of terms.
5 terms

Step 3. Divide the sum of the numbers by the number of terms.
35.5 / 5 = 7.1 chains

The average is 7.1 chains of fireline constructed per hour.

Range refers to the difference between the smallest number and the largest number possible for a given quantity.

Example 1 - Philip paces off some fire run distances and gets the following values in chains: 7.5, 6.0, 8.5, 5.5, 9.0. Find the range for the measurements.

Step 1. Arrange the numbers in ascending order (from the smallest to the largest).
5.5, 6.0, 7.5, 8.5, 9.0 

Step 2. Subtract the largest number from the smallest number.
9.0 - 5.5 = 3.5

The range is from 5.5 chains to 9.0 chains or 3.5 chains.

The deviation of a set of numbers is the difference between the average and the individual terms.

Example 1 - Jane paces off the following fire run lengths. Find the deviation of the fire run lengths, given as 6.5, 6.0, 8.0, and 7.5 chains.

Step 1. Calculate the average (see Section 9.3). Sum the numbers and divide by the number of individual elements: 28/4 = 7.0 

Step 2. Now, subtract each term from the average.
6.5 - 7.0 = -0.5
6.0 - 7.0 = -1
8.0 - 7.0 = 1.0 
7.5 - 7.0 = 0.5
These differences are the deviations.

Standard deviation, or variance, is a measure of the closeness of each term to the average (mean). If the terms are all close to the mean or average, then the standard deviation will be small and the mean can be considered an accurate approximation of the distribution.

To calculate to the standard deviation:
1. Compute each deviation as discussed on Section 9.4. 
2. Now, square each deviation and add the results all together. 
3. Finally, divide the calculated total by the number of terms minus one, and take the square root.

Example 1 - Find the standard deviation of this set of fire run distances: 9.0 chains, 12 chains, 11.5 chains, 12 chains, 9.5 chains. 

Step 1. Find the average (see Section 9.3).

9.0 + 12.0 + 11.5 + 12.0 + 9.5 = 54, 54 ÷ 5 = 10.8

Step 2. Find the deviation of each term (see Section 9.4).
9.0 - 10.8 = -1.8
12 - 10.8 = 1.2
11.5 - 10.8 = 0.7
12.0 - 10.8 = 1.2
9.5 - 10.8 = -1.3


Step 3. Square each deviation above.
(-1.8)² = 3.24
(1.2)² = 1.44
(0.7)² = 0.49 
(1.2)² = 1.44 
(-1.3)² = 1.69 


Step 4. Add the squared deviations together.
3.24 + 1.44 +0.49 + 1.44 + 1.69 = 8.30 

Step 5. Divide the sum of the squared deviations by the number of terms minus 1.
8.30 / (5-1) = 2.075

Step 6. Find the square root of the difference computed in Step 5.
√2.075 = 1.44

The standard deviation is 1.44 chains.

Hand crews primarily construct fireline but can also assist on hose lays, firing operations, protecting structures, mopping up, cleaning up, and other logistical support functions. It is important to match the task to crew capabilities. Use the best, most experienced crews for the toughest jobs and the hottest firelines. Crew effectiveness is controlled by these factors:

1. Leadership: Good, competent leadership is key to the success of the crew.
2. Training, Physical Fitness, and Experience: A crew that is well trained, in top physical condition, with several fires under the belt, will be very effective. A crew that is greatly trained and conditioned on the fireline increases the amount of line construction.
3. Crew-Member Turnover: Frequent changes in crew membership will erode the team aspects.
4. Morale: If a crew is "down", its productivity will be down.
5. Fatigue: Exhausted crew members will be ineffective, with a much higher potential for accidents.
6. Fuel, Weather, Topography, and Time of Day: In thick fuels and steep terrain, at the hottest time of the day, production will suffer. Working at night also will reduce production rates.
7. Fire Behavior: If the level of fire behavior is high to extreme, deploying hand crews will be very dangerous. Conditions should be considered and planned for accordingly.

When planning an attack on a fire, the length and width of the line must be estimated, along with the capabilities of the hand crew(s), to determine how many crews will be needed. Generally, a 15-person crew should be able to construct a 3-foot fireline around a 1-acre grass fire in 1 hour. Below are some average ideal rates for hand crew production rates in various vegetation.



Example 1 - Patricia spots a fire burning in open prairie. She determines that the fire has a perimeter of 1,800 feet. How many hand crews should she assign to construct a 3-foot line around the fire in 1 hour?

Step 1. Look under the column for grass vegetation of the hand crew production rates chart above. Follow the column down vertically.

Step 2. Look for the row that tells how much line a crew can cut per hour. Follow the row across horizontally. Where the two lines intersect is the number of lines per hour an average crew can cut in those conditions. 
One 15-person can cut 900 ft of line per hour

Step 3. Use this information to calculate the number of hours it will take one crew to construct 1,800 feet of line.


It will take 1 crew 2 hours to cut 1,800 feet of line.
Step 4. Determine how many crews it will take to construct the line in 1 hour.



To cut 1,800 feet of line in 1 hour, Patricia needs to assign two crews of 15 people each.
 

When arriving at a fire scene, always assess the entire situation to determine the best way to suppress the fire.