To Light a Fire

Subject:
General Science, Chemistry, and Physics

Theme:
Fires will not burn unless specific conditions exist.

OBJECTIVE

Students will learn to recognize and identify the conditions necessary for burning.

METHOD

In small groups, students will attempt to burn a variety of fuel types.

BACKGROUND

Fires need heat, fuel, and oxygen to burn. Remove any of these elements, and a fire will go out. In the northern Rockies, lightning provides a ready source of ignition. Fuels in the form of dead and down trees accumulate at a steady rate because the process of decay is slow in this region. However, conditions in Yellowstone are usually much too cold and wet to achieve large-scale, sustained burning. The drought of 1988 (conditions unprecedented in the park’s 112 year written record) was the key event that turned the tide in favor of burning. Severe drought accompanied by unusually high winds fanned the fires to their humbling proportions. In 1988, we witnessed a convergence of conditions, which rarely occurs. Forest fires burn in a mosaic pattern that is reflective of varying fuel types. Wet meadows and stands of young trees do not burn as readily as old forests with large accumulations of litter.

MATERIALS

Matches (enough for five per group)

Five buckets or boxes containing varying fuel types (keep the amount of fuel in each bucket small)

Bucket #1: A good assortment of sizes of fuels, some with needles, all green.

Bucket #2: Same as #1, but fuels should be dead and dry.

Bucket #3: Same as #2, but fuels should be damp.

Bucket#4: A good assortment of fuels, all partially burned.

Bucket#5: An assortment of fuels, all of large diameter (small surface area to volume ratio – i.e., no kindling.)

Plastic one-gallon containers filled with water, one for each fire.

PROCEDURE

Begin with a discussion of how a fire gets started and whether it is easy or difficult to start one. Instruct the students that they will be trying to start fires in small groups. It may not be easy! The groups must plan their strategies carefully. They will then try to get as much of their fuels to burn as possible in the allotted time. Read them the following rules:

1. Each group must be under the supervision of an adult.
2. All fires must be built within a designated area (an open playground or parking lot away from buildings would be best.)
3. No fuels may be used other than those assigned to each group.
4. Only five matches will be given to each group.
5. A two-minute group planning session prior to action is mandatory.

After all groups have had ample time (10 minutes should be adequate), call it quits and assemble groups for discussion. Which groups were successful? Why or why not? Visit each fire site and examine differences in fuel types and success of burning. Do these differences in fuel type occur naturally? Where and under what conditions can each be found? Discuss the extreme fire conditions of 1988, and ask kids to hypothesize as to whether or not it could happen again. What other factors besides fuel type come into play? Point out strategies observed, such as blowing on fires. Introduce a fire triangle model. Demonstrate that if any part is removed, the triangle will collapse and the fire will go out.

EXTENSIONS

Demonstrate burning in a bell jar:

1. Seal the jar with a stopper to cut off the supply of oxygen.
2. Add oxygen to demonstrate ignition of a glowing splint.
3. Observe the fire extinguish itself when the fuel is consumed.
4. You may also remove heat by adding water to extinguish.

SOURCE

Getting to Know Wildland Fire

A Teacher’s Guide to Fire Ecology in the Northern Rocky Mountains