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Matchstick Model

Cross Timber Woodland

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Laboratory Safety Review

On your student handout, write the three most important safety considerations.
Check with others in your group to add three more safety considerations to your list.
Are there any items from the “FireWorks Safety” poster that were forgotten? Add them to your list.

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Safety Checklist for Fire Activities

Wear appropriate Personal Protective Equipment [PPE].

100% cotton clothing; safety goggles; closed-toed shoes

Tie back loose sleeves and long hair.
Make sure a charged fire extinguisher is close. Know how to use it.
Make sure each station has a spray bottle that is filled with water.
Always be aware of the fire’s location. Never lean over the fire!
Extinguish burned materials with water before putting them in the trash. Fire is not out if there is any smoke or heat coming from the fuels.
If a fire starts on you … Stop! Drop! and Roll!

An instructor must be present for fire to be used.

(Adapted from the USFS “FireWorks Safety Poster”)

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Matchstick Cross Timbers Woodland

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The Fire Triangle

Conceptual Model
Fire has three components

Heat
Fuel
Oxygen

Heat

Fuel

Oxygen

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The Fire Environment Triangle

Conceptual Model
“Fire environment” has three components

Fuel
Weather
Topography

Weather

Fuel

Topography

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Fuel

The fuel in this experiment is simulated with matches

Fuel load - a measure of the potential energy that could be released by a fire
Fuel continuity - the amount of coverage, or distribution, of fuels (a major factor affecting the spread of a fire)

Let’s begin with fuel since it is also part of the fire triangle. From the fire triangle activities, we know that the combustion of fuel is an exothermic reaction; chemical potential energy is converted to light and heat energy. The fuel load is the amount of energy that could be released as a result of fuel type and/or quantity. Fuel continuity is important for this activity. Fuel continuity determines how easily fire can pass through an area. Click Are the fuels in this image continuous? Who would like to explain? Students should notice the bare soil and rocks which separate combustible clumps of biomass. What would be needed for a fire to move through this area? Answers might include: wind to carry embers/fire brands from one fuel source to the next; someone with a driptorch to light each clump of fuel; etc. Click In this image you can see that the matchstick model’s fuel continuity can be changed as well as fuel density and distribution. Click

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Weather

Weather factors influencing fire behavior

Temperature
Wind speed
Wind direction
Relative humidity

The fire triangle reminds us that heat is very important to fire. If it is very warm outside, fuels are already somewhat warm, and less heat will be needed to raise the fuels’ temperature to the ignition point. If you recall from the heat plume activity, wind can move heat into nearby fuels warming them up and drying them out which will make ignition easier. So wind speed and wind direction are extremely important. As air temperature changes, the maximum amount of water vapor that can be “absorbed” by the air also changes. If the amount of water vapor reaches the maximum amount, then the air is said to be saturated. Relative humidity is a measurement indicating the amount of water vapor present in air at a certain temperature expressed as a percentage of the amount of water vapor needed for the air to be saturated. Relative humidity affects fuel moisture. The drier fuel is, the quicker its temperature can reach the ignition point allowing fire to spread. Click

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Relative Humidity and Spotfires

Your group’s data may reveal some interesting trends. Here’s a graph showing information about spotfires. A spotfire is a fire started a distance away from a main fire by embers or flying sparks. Notice the burn crew dealing with a small spotfire outside of the larger burn unit. This graphical representation of data collected from prescribed burns in Oklahoma shows a relationship between relative humidity and the probability of a spotfire starting while conducting a prescribed burn. Can someone describe this relationship? As the RH increases the likelihood of spotfires decreases. If RH is below 25%, spotfires should be expected (100% probability). Does this relationship have a threshold? If RH is above 40%, the likelihood reaches a low percent probability that doesn’t vary much as RH continues to increase. When analyzing this activity’s data, pay attention to see if there are thresholds. Click

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Topography

Topography - the arrangement of the natural and artificial features of an area
Slope - ground that forms a natural or artificial incline

Slope is one topographical feature that can dramatically influence fire behavior. Click In a hilly or mountainous area, fire can move uphill Click or downhill. Slope is the rise or fall of a land surface. For this activity, slope will be measured in degrees using a protractor. Slope describes the angle of a surface measured from the horizontal. Thus, a horizontal surface has a slope of 0^o, and a vertical surface has a slope of 90^o. Just like in mathematics, an uphill slope is “positive” while a downhill slope is “negative.” The matchstick Cross Timbers model allows slope to vary so the effects on behavior and characteristics can be investigated as a fire moves up a slope Click, Click, Click or down a slope Click, Click, Click. Before we move on, get with your group and review the fire environment triangle information that has been added to your “Discussion Notes.” As students check each other’s work, walk around the class to be sure the basics of fuel, weather, and topography are understood.

Now it’s time to design some experiments! Click

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Experimental Design

Controlled experiment

Independent variable

The factor changed by the investigator
For this activity, limit your changes to one variable
Changing the independent variable is a “treatment”

Dependent variable

Values measured will be influenced by the investigator changing the independent variable
How will this be measured?

Each group will design and carry out controlled experiments to learn about the relationships between fire behavior or fire characteristics and some of the variables in the Fire Environment Triangle. Let’s quickly review what the important components of a controlled experiment are. For this activity, “controlled” means that you will change or vary only one independent variable for each investigation you perform. Your group will adjust/change/vary that independent variable for each experimental trial. Your group should do their best to “control” everything else in the experiment so you can determine how the only factor being changed, the independent variable, affects the dependent variable. As a group, refer to the notes you took and decide which factor could be varied or changed with the materials provided for this activity. Once your group has decided upon an independent variable, think of what the dependent variable might be and how you could measure changes in the dependent variable with the materials provided. Remember that a smartphone or computer could be used as a stopwatch. It might be possible to measure multiple dependent variables during each trial, so each group could have multiple hypotheses being tested with one experiment. Make yourself available to students as they design their experiments. When it appears that students are making good progress with the variables, their hypothesis, etc. go to the next slide. One last slide before you begin your experiment. Click

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Experimental Results

Graphical analysis/analyses of data

X-axis - independent variable
Y-axis - dependent variable

Scatter plot

Determine the relationship or trend using the “best fit”

Curve or line
Do not “connect the dots”

Relationship between variables?
Was there a “threshold” in the relationship?

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Experimental Results/Data Analysis

Relationship between variables?

Positive correlation - as one variable increases so does the other.
Negative correlation - as one variable increases, the other decreases.
No correlation - there is no apparent relationship between the variables.

Was there a “threshold” in the relationship?

As you graph your data and perform an analysis with a best fit curve/line, look for the relationship between the independent and dependent variables. Read the three bold-faced terms and their definitions. Also be looking for a threshold where the relationship changes in some important way similar to the spotfire example. Click What kind of correlation do the independent and dependent variable have in this graph? Give students an opportunity to describe the correlation. Click As you can see, there is a negative correlation. Does there appear to be a threshold? (no) Click … in this graph? Click (positive correlation) … threshold? (no) Click … in this graph? Click (no clear correlation) … threshold? (no) If you are familiar with statistics, you could mention the importance of the R² value in the graph. If not, don’t worry about it. Click

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Experimental Conclusion(s)

Did your results support or disprove the hypothesis/hypotheses? (CER format)
Conclusion or Claim
Evidence
Reasoning or Rationale

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Experimental Design

Make appropriate tables for recording data

Independent variable treatments
Dependent variable measurements

Each group must have teacher approval before beginning an experiment
Groups should conduct one test burn before doing the full experiment to test procedures (make necessary changes)
Monitor for the safety of your group and other groups
Report any safety concerns immediately!

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Safety Checklist for Fire Activities

Wear appropriate Personal Protective Equipment [PPE].

100% cotton clothing; safety goggles; closed-toed shoes

Tie back loose sleeves and long hair.
Make sure a charged fire extinguisher is close. Know how to use it.
Make sure each station has a spray bottle that is filled with water.
Always be aware of the fire’s location. Never lean over the fire!
Extinguish burned materials with water before putting them in the trash. Fire is not out if there is any smoke or heat coming from the fuels.
If a fire starts on you … Stop! Drop! and Roll!

An instructor must be present for fire to be used.

(Adapted from the USFS “FireWorks Safety Poster”)

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Class Presentations

As your classmates present, complete the “Presentation Table” by filling in each space with focused notes about each group’s experiment

Key words
Graphs
Diagrams