This module provides a brief overview of wildland fire history and the influence that fire has had on cultural mythology around the world. Module 1 also addresses the general principles of fire that are applicable to both wildland and structural fire. These principles include elements required for a fire to burn, and some definitions pertaining to fire effects. Understanding these principles is essential to understanding fire.
Demonstrate knowledge of fire including the components necessary for fire, combustion, and ways to put a fire out.
The origin of fire is tied to the origin of plants. Plants are responsible for two of the three elements essential to the existence of fire: oxygen and fuel. The third element, a heat source, has been available throughout the history of Earth—mainly through lightning (Pausas and Keeley 2009).
Plants and trees smoldering from a lightning strike or any source of hot coals may have been the first resources exploited by humans to control fire. Friction using the flint-and-steel method, where hot sparks are struck from a piece of steel or iron onto suitable tinder, was a commonly used primitive technique for making fire. Fire was used as a tool to clear ground for human habitats, to facilitate travel, to kill vermin, to hunt, to regenerate plant food sources (for both humans and livestock), to use for signaling, and even to use in warfare among tribes.
Much is written about the dense, primeval forests of North America—from coast to coast. Equally impressive to early European settlers were the great open expanses of prairies, meadows, and savannas, most of which were created and maintained by native burning (Figure 1).
A story on native burning was written by Sharon Levy (2005), a freelance writer in Arcata, California. Levy wrote about Amelia Lyon, who was a member of the Hupa Tribe of northern California. Amelia practiced what generations of women in her culture did—maintaining the open oak woodlands near what is now Redwood National Park. Amelia tended the open oak stands by burning the undergrowth every year and thereby encouraging health and vigor in the standing trees, and more importantly, generous acorn crops. Since her death in the late 1800s, the native tradition of burning ended.
Other historical accounts suggest that the Takelma women (from the Rogue Valley of interior southwest Oregon) were responsible for the majority of the seasonal burns used for harvesting foods (Tveskov et al. 2002). They used fire to roast and collect sunflower and tarweed seeds, grasshoppers, and yellow jacket larvae, and to make it easier to locate acorns for collection while also suppressing boring insects. These regular fires in the oak or grass savanna also encouraged the growth of healthier basketry materials; the same was done at higher elevations to encourage the new growth of beargrass, the leaves of which are another important basket-weaving and regalia-making material.
An expansive, grassy oak savanna is the perfect foraging ground for game animals like deer and elk. When the Takelma burned the oak savanna, keeping trees and brush out and grass growth abundant, they also ensured the deer and elk populations would stay in the area, providing an important meat source.
When it was time to hunt the mammals, larger fires were used once again for deer drives, frightening the scattered deer into smaller areas and eventually trapping them in a brush enclosure where hunters waited.
In some instances, the Takelma used fire during warfare to scare away or hinder travel of competing tribes or to use the smoke to cover up an escape. They also used fire to burn potential enemy hiding places and to signal war activity to nearby groups (Tveskov et al. 2002, Pullen 1996, LaLande and Pullen 1999).
For the Takelma, fire was an essential tool for maintaining healthy food sources year after year. As a result of the tarweed seed, grasshopper, and deer-drive burns, overgrowth of brush and small trees was kept to a minimum, maintaining a larger open, oak savanna. The Takelman use of anthropogenic fire provided them with sustainable food resources, but also maintained a healthy habitat for large game animals, encouraged biological diversity, minimized fuels, and decreased the probability of catastrophic wildfires (LaLande 2004).1
Legendary forest fires like the Peshtigo Fireof 1871 in Wisconsin and the Great Fire of 1910 in Montana and Idaho bolstered the argument that forest fires threatened commercial timber supplies and contributed to the philosophy that fire was a danger that needed to be suppressed. Before the middle of the 20th century, most forest managers believed that fires should be suppressed at all times. By 1935, the U.S. Forest Service’s fire management policy stipulated that all wildfires were to be suppressed by 10a.m. the morning after they were first spotted. Complete fire suppression was the objective. In 1968, policies started to shift and the National Park Service changed its policy to recognize fire as an ecological process. The Forest Service followed suit in 1974 by changing its policy from fire control to fire management. Current fire suppression efforts by land managers have focused on protecting the public, the wildland-urban interface (WUI), and other valuable resources.
Shifts and changes in policy and management have altered fire regimes over time. Historically high-frequency, low-severity fire regimes have been replaced with low-frequency, high-intensity crown fires that are outside the natural range of variability.
How do we know what the historic fire regimes were? There are several methods to measure and assess fire and disturbance history through time. Ice core analysis is one method that has been conducted for the last 40 years by measuring gases and charcoal sediments trapped in the ice. Measurements can go back in time over 100,000 years.
The negative aspects are that ice core measurements are by necessity taken in remote sites and do not measure local vegetation variability.
One study conducted by Zennaro et al. (2014) measured 2,000 years of boreal forest fire history from Greenland. Fourteen major events (“megafires”) were recorded where fires of such great magnitude burned that charcoal from plumes carried to Greenland were deposited.
The highest concentrations of charcoal in ice cores from Greenland coincide with Viking settlements during the “Little Climatic Optimum” between 920 and 1110 Common Era (CE). The lowest concentrations of charcoal in ice cores was measured during the “Little Ice Age” between 1400 and 1700 CE. Another rise was measured during 1910 when the Great Fire occurred in Montana and Idaho.
Dendrochronology is another method of measuring fire and disturbance history. It is the extraction of tree cores to measure growth rings and fire scars (Figures 2 and 3). This method is site specific and is good for mapping fire history across a landscape. Also, this method can illustrate the level of fire intensity—assuming the tree survived a wildland fire—and frequency for potentially hundreds of years. Disadvantages are that the record is limited to certain species (trees prone to heart rot cannot be measured) and only measures back a few hundred years at most (the lifespan of most tree species). Another disadvantage is that high-intensity fires cannot be measured due to mortality of trees, and very low-intensity fires cannot be measured because they are not intense enough to leave a scar, and therefore be recorded in growth rings.
Sediment (including pollen, sediment, and charcoal) cores have also been used to measure disturbance history. Similar to tree cores, these cores may not give a clear picture of low-intensity fires and are relatively site specific—primarily to water-prone, micosites, extracted from lakes, fens, and/or bogs. The measurement is also restricted to certain species of tree, shrub, and grass due to the nature of pollen decomposition of certain species. However, these cores can give a good vegetation succession history that can go far back in time—potentially over thousands of years. For example, a measurement core was taken in a western red-cedar/hemlock plant association in northwest Montana. Precipitation at the time (1995) was about 70 inches annually, which resulted in the warm and moist conditions suitable for those species. The sediment core measured back 7,000 years and illustrated a changing climate and different vegetation—as well as different fire frequencies and severities. On this particular landscape, 4,000 to 7,000 years previous, the climate was cooler and drier with subalpine fir being the dominant species. From 2,500 to 4,000 years previous, the climate was cooler and drier with true fir (Abies) being the dominant species. The current vegetation assemblages did not appear dominant in the record until 2,500 years from the present time of measurement (Chatters and Leavell 1994).
A correlation was made to regional temperature measurements, available moisture, regional flooding events, and native population rises and declines (Figure 4).
Humans have had profound impacts on fire history and consequently have altered fire regimes across the landscape. The interaction between fire and anthropogenic-induced climate change contributes to future uncertainty. For example, an increase in the frequency of extreme droughts as a result of climate change may facilitate the spread and intensity of fires. An increase in global temperature may also alter fuel continuity in very different ways in different ecosystems (Figure 5). An understanding of the natural range of variability, both past and future, in which a forest will remain resilient, dynamic, and productive is helpful for developing forest- and fire-management activities for the future.
Fire can be a friendly, comforting thing, a source of heat and light, as anyone who has ever sat by a campfire in the dark knows. Yet fire can also be dangerous and deadly, racing and leaping like a living thing to consume all in its path. In the mythology of virtually every culture, fire is a sacred substance that gives life or power.3
Agni, the god of fire in Hindu mythology, represents the essential energy of life in the universe (Figure 6). He consumes things, but only so that other things can live. Fiery horses pull Agni’s chariot, and he carries a flaming spear. Agni created the sun and the stars, and his powers are great. He can make worshipers immortal and purify the souls of the dead from sin. One ancient myth about Agni says that he consumed so many offerings from his worshipers that he was tired. To regain his strength, he had to burn an entire forest with all its inhabitants.
Chinese mythology includes stories of Hui Lu, a magician and fire god who kept 100 firebirds in a gourd. By setting them loose, he could start a fire across the whole country. There was also a hierarchy of gods in charge of fire. At its head was Lo Hsüan, whose cloak, hair, and beard were red. Flames spurted from his horse’s nostrils. He was not unconquerable, however. Once, when he attacked a city with swords of fire, a princess appeared in the sky and quenched his flames with her cloak of mist and dew.
A number of Native American cultures believe that long ago some evil being hid fire so that people could not benefit from it. A hero had to recover it and make it available to human beings. In many versions of the story, a coyote steals fire for people. Sometimes a wolf, woodpecker, or other animal steals the fire. According to the Navajo, a coyote tricked two monsters that guarded the flames on Fire Mountain. Then he lit a bundle of sticks tied to his tail and ran down the mountain to deliver the fire to his people.4
In the Christian belief system, the Devil himself appears in some fire-related folktales. In parts of Europe, it is believed that if a fire won’t draw properly, it’s because the Devil is lurking nearby. In other areas, people are warned not to toss bread crusts into the fireplace because it will attract the Devil (although there’s no clear explanation of what the Devil might want with burnt bread crusts).5
The manifestation of the divine in the form of fire may be found in the Abrahamic faiths as well. In Christianity, for example, the Holy Spirit is said to have descended on the apostles in the form of tongues of fire on the day of Pentecost. The manifestation of God in the element of fire is also found in the Old Testament, as evident from a passage in the book of Exodus where God spoke to Moses from the burning bush. Abrahamic faiths also acknowledge the destructive power of fire. The destructive dimension of this element is at times associated with the wrath of God, and a number of verses from the Bible have been used to illustrate this. Another way of interpreting the destructive power of fire is to view it as a means of purification. In other words, fire could be symbolically seen as a way to ‘burn’ away one’s evil urges.6
According to the National Park Service (NPS.gov), fires remove dead trees and litter from the forest floor. Shrubs and trees invading grasslands also are killed by fires. In each example, new healthy regrowth occurs. Fire does not imply death, but rather change. As fire was associated with rebirth and renewal in mythology, so fire is now recognized as an instrument of change and a catalyst for promoting biological diversity and healthy ecosystems.
Fire is a chemical reaction in which energy in the form of heat is produced. The chemical reaction is known as combustion. Combustion occurs when fuel or other material reacts rapidly with oxygen, giving off light, heat, and flame. A flame is produced during the ignition point in the combustion reaction and is the visible, gaseous part of a fire. Flames consist primarily of carbon dioxide, water vapor, oxygen, and nitrogen.
Combustion is the opposite process of photosynthesis. Combustion is the breaking apart of the building blocks put together through photosynthesis. Combustion is the release of the energy acquired during photosynthesis. Oxygen is introduced, and bonds in the fuel of hydrogen and carbon are broken (releasing energy), the resulting hydrogen and carbon combining separately with the oxygen as H2O and CO2, releasing heat in the process. Photosynthesis is the process of plants slowly absorbing the energy (heat) from the sun and building/growing tissue (Figure 7). Carbon dioxide is stored in the tissue, and oxygen is given off into the atmosphere. Combustion is the process of that tissue (plant matter) burning—oxygen is consumed, and carbon dioxide and heat are released into the atmosphere.
The fire triangle includes the three components that must be present for a fire to burn. These components are fuel, oxygen, and a heat/ignition source (Figure 8). Without one of these components, fire cannot exist. For a fire to ignite, there must be an initial and continued heat source—this is called a chain reaction and is part of what makes up the fire tetrahedron.
Heat allows fire to spread by removing the moisture from nearby fuel, warming surrounding air, and preheating the fuel in its path. When the fire becomes either fuel-controlled (i.e., there is no more fuel to burn) or ventilation-controlled (i.e., there is not enough oxygen to sustain combustion), the fire decays to a smoldering state.
Four ways to put out a fire:
Heat/ignition sources include anything capable of generating heat—lightning, cigarettes, powerlines, catalytic converters, small engine sparks, matches, a magnifying glass.
Fuel sources include any kind of combustible material—grass, shrubs, trees, houses, propane tanks, wood piles, and decks.Fuels are characterized by their moisture content (how wet the fuel is), size, shape, quantity, and the arrangement in which they are spread over the landscape.
The last part of the triangle is oxygen. Ambient air is made up of approximately 21 percent oxygen and most fires require at least 16 percent oxygen content to burn. A fire ignited in an area that has little oxygen will support only a small flame.
If oxygen is suddenly and rapidly added to a nearly suffocated fire, the re-oxygenated air will quickly ignite, creating large and dangerous flames known as a flashover or backdraft.Flashover is a term used in structural firefighting and is by definition “the sudden involvement of a room or an area in flames from floor to ceiling caused by thermal radiation feedback.” A flashover reaches high temperatures (over 1,000oF) so quickly that all flammable contents spontaneously ignite and conditions become untenable and unsafe.
A backdraft is a smoke explosion that occurs when additional air is introduced to a smoldering fire and heated gases enter their flammable range and ignite with explosive force. A backdraft is an air-driven event, unlike a flashover, which is temperature driven. The fact that most fires are air regulated and not fuel regulated makes the understanding of backdrafts so important.
A “flashover” in the wildland environment is called a Generalized Blaze Flash (GBF) phenomenon. The GBF is defined as a rapid transition from a surface fire exhibiting relatively low intensity to a fire burning in the whole vegetation complex, from surface to canopy, and demonstrating dramatically larger flame heights, higher energy release rates, and faster rates of spread. This can occur when the ambient air temperature rises dramatically, the relative humidity drops significantly, and the wind speed rises. When all three conditions occur in the wildland, a GBF can develop from a slow-moving ground fire to a raging crown fire. All fuel (forest, range, grassland) burns simultaneously. From all appearances, this looks, acts, and feels just like a flashover in a confined space structure—but over many acres in a wildland setting.
While the fire triangle describes the components required to sustain a fire, the fire behavior triangledescribes the components that determine how a fire burns—topography, weather, and fuels. Fuels is the common denominator between the two triangles. The fire behavior triangle and its components will be covered in more depth in Fire Behavior Module 3.
Fire intensity and fire severity will be defined in more detail in Module 3 but, for now, it helps to understand that fire intensity and fire severity both characterize a fire but describe entirely different concepts. Fire intensity is the amount of heat (energy) given off by a forest or structure fire at a specific point in time (Figure 9).
Fire severity is a product of fire intensity and residence time, and refers to the effects of a fire on the environment, typically focusing on the loss of vegetation both aboveground and belowground but also including soil impacts (Figure 10).
While a fast-moving, wind-driven fire may be intense (lots of heat), a long-lasting fire that just creeps along in the forest underbrush could transfer more total heat to plant tissue or soil in a given area. In this way, a slow-moving, low-intensity fire could have more severe and complex effects on something like forest soil than a faster-moving, higher-intensity fire in the same vegetation. (Hartford and Frandsen 1991).
Fire conditions can also vary considerably throughout a structure. One area of the building could be in a fully developed stage while a different area might be in the growth or decay stages of the fire. Like in wildland fire, the intensity and severity of these fires at each stage will depend on available heat, fuel, and oxygen (Figure 11).
Fire developmental stages include (Figure 12):
Development of the incipient fire is dependent on the characteristics and configuration of the fuel involved. If there is adequate oxygen, additional fuel will become involved and the heat release rate from the fire will increase; this is considered the growth stage. The flashover point is the sudden transition from a growth stage to fully developed fire. When flashover occurs, there is a rapid transition to a state of total surface involvement of all combustible material within the compartment. In the post-flashover stage, energy released is at its greatest but is limited by ventilation. When the available fuel is consumed or there is limited oxygen, the fire is then considered in decay stage (Hartin 2008).
The facilitator should secure a room large enough to comfortably accommodate participants. Organize the room in a U‐shape fashion with long tables and chairs. The room should have a large screen to display the presentation. There should be a large table up front (6 to 8 feet in length) for the instructor to use for in‐class demonstrations and to display various props. The room should be equipped with a fire extinguisher, water faucets (or access to a water supply), and be suited for demonstrations that require the use of fire.
Approximately 6 hours in the classroom
Student evaluation—Have a set of questions that touch on the different topics covered in the module. Ask people to provide thoughts and discussion on one or two questions. The instructor should then evaluate and weigh in on the discussion.
Class evaluation—Provide a survey for student feedback for each module as a form of formative evaluation.
I. Fire Starting
II. Tree Examinations
III. (con’t) Personal and Professional Insights
Fire, fire, fire. Not that it means anything, but he was born in March—on a date that is supposed to be influenced by the fire sign. Adults told him later that when around 2 to 3 years old he played alone in the utility room where his cot lay.
He found a screwdriver and tried to take apart the bare-wire socket hanging on the wall. When the adults rushed in through the smoke, the wall had caught on fire and he stood there laughing at the flames.
Growing up poor, he had no store-bought toys, but delighted by the hour in building model homes, trees, cars, and people out of scraps of cardboard. When the city was finished, he would burn it all down with matches stolen from the kitchen—or with the magnifying glass—or the butt-