ch 5. Fire Environment

Question 1

wildland fire environment consists of three major components

Answer 1

1. topography
2. fuels
3. weather

Question 2

of the three environmental factors, which is the most variable

Answer 2

weather

Question 3

what are the elements of weather that will affect fire behavior

Answer 3

1. wind speed and direction
2. relative humidity
3. temperature
4. atmospheric stability
5. precipitation

Question 4

some areas of the Country, what is the 6th important factor in other areas of the Country, not a major concern in Southern California

Answer 4

Lightening

Question 5

a wind of 15 MPH exerts about ___ pound of pressure on a one foot square surface

Answer 5

one

Question 6

30 MPH wind will exert __ pounds of pressure

Answer 6

4.5

Question 7

60 mph wind will exert __ pounds of pressure

Answer 7

18

Question 8

doubling wind velocity will approximately ___ the rate of fire spread

Answer 8

quadruple

Question 9

most severe weather condition for brush fires in our area is

Answer 9

dry Foehn wind (Santa Ana), blows from the north

Question 10

Santa Anas are most common in cool months such as

Answer 10

September through April

Question 11

how long do Santa Anas usually last

Answer 11

two to three days, getting weaker each day

Question 12

average speed of up canyon, daytime winds are about

Answer 12

10-15 MPH

Question 13

Down canyon, night flows average ___ mph

Answer 13

5-8

Question 14

Common thunderstorm wind speeds

Answer 14

20 to 30 MPH
60 to 75 MPH are possible

Question 15

what are the most common indications of intense local heating and unstable air conditions

Answer 15

whirlwinds or dust devils

Question 16

relative humidity doubles with each __ degree decrease in temperature and is halved with each __ degree increase in temperature within an air mass

Answer 16

20
20

Question 17

ignition temp of brush various between ___ and ___ F

Answer 17

400 and 700

Question 18

Practical average temperature ignition temp for brush is considered to be about ___ F

Answer 18

540

Question 19

Practical average temperature ignition temp for brush is considered to be about ___ F

Answer 19

540

Question 20

What is the most constant of the three major components of the fire environment

Answer 20

Topography

Question 21

What is the most important factor under topography

Answer 21

steepness of slop

Question 22

Fuels on what side of slopes have more fires because they cure out earlier in the year, and typically smaller and drier. Relative humidity is lowest on these slopes

Answer 22

South and West

Question 23

What side of slopes typically have the heaviest fuels, highest fuel moisture, lowest average temperature, lowest rate of spread of fires and lowest fire starts

Answer 23

North slopes

Question 24

What part of the environment carry the fire

Answer 24

Fuels

Question 25

fuels can be classified in three basic categories

Answer 25

1. Grasses and weeds (Light fuels)
2. Coastal sage scrub (moderate fuels)
3. Mixed chaparral (Heavy Fuels)

Question 26

Dead branches and twigs frequently make up ____ to ____ of the fuel volume in chaparral stands more than 30 years old

Answer 26

1/3 to 1/2

Question 27

What is generally considered the most important influence on flammability of fuels

Answer 27

Moisture content

Question 28

Grasses and weeds are light fuels and compose what we call them as

Answer 28

flash fuels

Question 29

Coastal sage scrub only grows about ___ feet in height

Answer 29

four

Question 30

Mixed chaparral grows up to __ feet and found mostly on north facing slopes

Answer 30

20 feet

Question 31

criteria for fuel model “B” is

Answer 31

Woody plants 6 ft or greater which occupy 2/3 or more of a particular brush site. 1/4 of the site must be dead fuel