Wildfire 101: The Fire Triangle and The Fire Tetrahedron

There are three components needed to start a fire: fuel, oxygen, and heat. This is commonly referred to as the fire triangle. If any one of the components is missing, a fire cannot occur.


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 Artist’s rendition of the Fire Triangle – Source: USFWS Alaska

The Fire Triangle is a simple way of understanding the three elements a fire needs to ignite: each side of the triangle represents one of the three ingredients – oxygen, heat, and fuel – demonstrating the interdependence of these ingredients in creating and sustaining fire. A fire naturally occurs when the elements are present and combined in the right mixture, meaning that fire is actually an event rather than a thing. When there is not enough heat generated to sustain the process, when the fuel is exhausted, removed, or isolated, or when the oxygen supply is limited, then a side of the triangle is broken and the fire will die.

Heat – A heat source is responsible for the initial ignition of fire, and heat is also needed to maintain the fire and permit it to spread. Heat allows fire to spread by removing the moisture from nearby fuel, warming surrounding air, and preheating the fuel in its path, enabling it to travel with greater ease. Heat can be removed by the application of a substance which reduces the amount of heat available to the fire reaction. This is often water, which requires heat for phase change from water to steam.

Fuel – Fuel is any kind of combustible material, and is characterized by its moisture content (i.e. how wet the fuel is), size and shape, quantity, and the arrangement in which it is spread over the landscape. The moisture content determines how easily that fuel will burn. Fuel can be removed naturally, as when the fire has consumed all the burnable fuel, or manually, by mechanically or chemically removing the fuel from the area.

Oxygen – The oxidizer is the third component of the chemical reaction.  In most cases, is simply comprised of the ambient air, and in particular one of its components, oxygen. Air contains about 21% oxygen, and most fires require at least 16% oxygen content to burn. By depriving a fire of air, it can be extinguished.

2000px-Fire_tetrahedron.pngThe Fire Tetrahedron (wikipedia)

In recent years, fire experts have redefined the triangle to a tetrahedron, adding an actual chemical chain reaction component to the three already present in the fire triangle. Basically, while the three classic components are still needed, an actual chemical reaction must take place in order for the fire to ignite.  Once a fire has started, the resulting exothermic chain reaction sustains the fire and allows it to continue until at least one of the elements of the fire is blocked. As with the fire triangle, as soon as one of the four elements of the tetrahedron is removed, combustion stops and the fire is extinguished.

Source: www.smokeybear.com

Fire Danger Signs: What Do They Really Mean?

Ever been driving along a highway, spotted a Fire Danger Sign, and wondered what it is truly indicating?

Fire Danger is a description of the combination of both constant and variable factors that affect the initiation, spread, and difficulty to control a wildfire in a given area. There are many systems and schemes that attempt to provide accurate and reliable predictions of fire danger, that analyze the fuel, topography, and weather, and integrate their effects into a set of numbers that fire managers can use to determine a rating.

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Since 1974, five rating levels have been used to describe danger levels in public information releases and fire prevention signing:

Low (Green) – Fire starts are unlikely. Weather and fuel conditions will lead to slow fire spread, low intensity and relatively easy control with light mop-up. Controlled burns can usually be executed with reasonable safety.

Moderate (Blue) – Some wildfires may be expected. Expect moderate flame length and rate of spread. Control is usually not difficult and light to moderate mop-up can be expected. Although controlled burning can be done without creating a hazard, routine caution should be taken.

High (Yellow) – Wildfires are likely. Fires in heavy, continuous fuel such as mature grassland, weed fields and forest litter, will be difficult to control under windy conditions. Control through direct attack may be difficult but possible and mop-up will be required. Outdoor burning should be restricted to early morning and late evening hours.

Very High (Orange) – Fires start easily from all causes and may spread faster than suppression resources can travel. Flame lengths will be long with high intensity, making control very difficult. Both suppression and mop-up will require an extended and very thorough effort. Outdoor burning is not recommended.

Extreme (Red) – Fires will start and spread rapidly. Every fire start has the potential to become large. Expect extreme, erratic fire behavior. NO OUTDOOR BURNING SHOULD TAKE PLACE IN AREAS WITH EXTREME FIRE DANGER.

– See more at: http://www.nps.gov/fire/wildland-fire/learning-center/fire-in-depth/understanding-fire-danger.cfm#sthash.qf9PGgN8.dpuf

Powerline Fire in Big Bend National Park nearing full containment

A wildland fire started in Big Bend National Park, Texas, around 5:00 PM on Monday, February 1st, when heavy winds caused a power line to fall. The fire burned grassland and brush habitat, and is estimated to have been around 1,800 acres in size.  It is now 100% contained.

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Powerline Fire as seen in our Incident Dashboard

Heavy winds originally pushed the fire to the east and northeast of Panther Junction during the evening of February 1st, and the fire covered 500 acres by Monday evening. By Tuesday afternoon the fire had spread to over 1,000 acres as winds continued to blow. A combination of National Park Rangers and fire crews battled the fire, working 10-12 hour shifts at a time. Higher humidity, colder temperatures, and somewhat diminished winds on Wednesday helped slow the fire during the evening hours, along with firefighter efforts to work hot spots along the fire perimeter.

Electrical power was initially lost to the Panther Junction, Chisos Basin, and Rio Grande Village areas, but was restored as of February 3rd. Additionally, two park roads, the road to Rio Grande Village and Old Ore Road, were closed as a precaution but both roads were re-opened on February 2nd.

No park structures were damaged, and no injuries were reported during the initial fire or suppression efforts.

Source : http://inciweb.nwcg.gov/incident/4659/

Texas’ Significant Wildfire Potential

According to Texas Forest Service’s Dispatch Tracker, the weekend produced multiple red flag warnings and 20 new fires totalling over 1,700 burned acres in the State of Texas. Despite the weekend’s elevated fire weather conditions and activity, Texas’ wildfire potential remains normal to below normal into early summer.

 

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February’s Significant Wildfire Potential

WILDFIRE POTENTIAL OUTLOOK FOR TEXAS 

Normal significant wildland fire potential and some areas of Below Normal significant wildland fire potential are expected for the state through May.

Weather & Fuels:

In January, the Plains states, from Texas to North Dakota, were very dry with generally less than 50 percent of normal precipitation for the month. But El Nino conditions and the expected jet stream path are forecast to bring above average precipitation and below average temperatures to most of the state into early summer. As a result, fuel moistures are projecting to remain above critical levels except for a few seasonably typical periods of low humidity, winds, and warm temperatures creating brief elevation of initial attack potential. All indications from Predictive Services (NIFC) point to these brief periods of elevated potential as the dominant concern for significant fire activity for the area in the coming months.

Source: NIFC Predictive Services (Outlook PDF)

 

Fuel Reduction Practices and Purpose

The practice of hazardous fuel reduction is most often associated with moderating the flammable vegetation around the defensible space of individual homes and communities. But this proactive approach to fighting wildland fire comes in many other forms and, unlike fire-fighting in most areas, is a year-round practice. 

 

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Ridgeline fuel break example on the left and a road brushing/shaded fuel break on the right.

The basic function of a fuel-break is to impose some obstacle to the spread of potential fire, and also to provide access to the fire should one break out. Fuel breaks are designed to change the behavior of a wildfire by reducing the quantity, density, and configuration of potential fuels that the fire encounters when it enters the fuel break. 

Breaks are constructed for a number of purposes:

  • To act as a barrier to control the spread of a fire to a particular area or property.
  • To contain the spread of a fire from a fire source.
  • To break up large fuel areas (i.e. where fire may spread rapidly or be difficult to control, a system of firebreaks is sometimes established to aid in confining the fire to a relatively small area).
  • Reduce a crown fire to a fire burning on the ground. 

Fuel Breaks are most effectively located in the following areas:

  • Along ridges, where fires naturally slow their progress under most conditions.
  • 100 feet to 200 feet around structures, where fires are likely to start.
  • Along roads, power lines, and pipelines, where openings already exist.
  • Around wet areas, rock outcrops, mined areas, and other topographically strategic locations where fire spread may be reduced.
    • Adjacent to areas where fuel reduction treatments, such as thinnings and surface fuel treatments, have already been performed, where fire intensity and spread are already reduced.
    • Connecting to existing fuel breaks, to expand protected areas in a systematic way.

Natural Resources Conservation Service (CA) – Code 383

It’s Prescribed Fire Season

In many wildland areas, smoke can often be seen throughout the winter. More than likely, this is not due to uncontrolled wildfire, but rather prescribed fires that are started when the weather is less conducive to catastrophic burns, allowing firefighters and crews to prepare for when wildfire season picks up again.  

 

30230_628921240365_2148150_n.jpgA Rx fire (controlled pile burning) I helped ignite in Golden Hills near Tehachapi, CA

Prescribed fire is one of the most effective mitigation concepts for reducing the outbreak and spread of wildfires. SmokeyBear.com defines prescribed fire as the controlled application of fire by a team of fire experts under specified weather conditions that help restore health to fire-adapted environments.  Prescribed fires can sometimes be confused with “backfiring” or “controlled burning” which typically refer to different types of prescribed and controlled fires. In many cases by safely reducing excessive amounts of brush, shrubs, and trees, prescribed burning can help reduce the catastrophic damage of wildfire on wildlands and surrounding communities.

In the Golden Hills photo above, the piling and burning of excess fuel was intended to make the fire road safer (this technique is sometimes called road brushing) and also to provide a fire break between Hwy 58 (a major thoroughfare) and the densely populated Golden Hills community.

Smoke Color Can Depict Fuel Type

Smoke is made up of particulates, aerosols and gases, and identifying the characteristics of each in a given smoke plume can be helpful when fighting fires. Reading smoke can tell a firefighter what is currently happening with a fire as well as what might happen in the future. One particularly important factor in predicting fire behavior is the color of the smoke emitted.

 

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Smoke is the biproduct of the fuels it is burning.  The color of the smoke indicates to firefighters the type and density of the fuels involved, all of which gives hints as to what the fire might do next.

White smoke can often mean material is off-gassing moisture and water vapor, meaning the fire is just starting to consume material. White smoke can also indicate light and flashy fuels such as grass or twigs.

Thick, black smoke indicates heavy fuels that are not being fully consumed. At times, black smoke can be an indicator that a manmade material is burning such as tires, vehicles or a structure. As a general rule, the darker the smoke, the more volatile the fire is.

Grey smoke can indicate that the fire is slowing down and running out of materials to burn.

2015 Wildfire Acreage Tops 10 Million for the First Time

2015 was a significant year for wildfires with the total acreage cresting 10 million for the first time on record. To put it in perspective, 10 million acres is roughly 7.5 million football fields, 12,000 Central Parks, or 15 Rhode Islands.

 

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Reported Wildfires from GeoMac and Fire Statistics from NIFC

2015 actually saw fewer fires than the 10-year average, but the total acres burned was more than 3.5 million greater than average. Alaska’s dozens of huge wildfires accounted for more than half of the total acres burned nationwide. Acreage-wise, an area the size of the entire state of Massachusetts burned inside of Alaska.

The Rocky Mountain and Southwest regions were quieter than normal. Major wildfire complexes raged for weeks in Idaho, NE Washington, Northern California, and Oregon. In terms of destruction, Northern California’s Butte and Valley wildfires combined to destroy 818 and 1958 structures respectively, the 7th and 3rd most in the state’s history.

WildFire 101: Haines Index

Haines Index is used to indicate the potential for rapid fire growth due to dry and unstable atmospheric conditions over a fire area. The index is a simple way to measure the atmosphere’s contribution to the fire’s growth potential. A high Haines Index is correlated with large fire growth where winds do not dominate fire behavior.

During days with a high Haines index and a Lightning Activity Level (LAL) above 4, fire behavior can become very erratic, unpredictable and difficult for resources to control and contain.

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2014 Incident Response Pocket Guide, Page 65

Wildfire 101: Lightning Activity Level (LAL)

The Lightning Activity Level (LAL) is a measurement of cloud-to-ground lightning activity observed (or forecasted to occur) within a 30 mile radius of an observation site.

 

 The LAL is part of the National Fire Danger Rating System (NFDRS) and consists of two reports. The first report covers the period from the previous day’s observation until midnight (referred to as Yesterday’s Lightning) and the second report covers the period from midnight until the present day’s observation time (referred to as Morning Lightning).  Each report is assigned a number on a scale of 1 to 6 which reflects the frequency and character of the lightning. The scale for 1 to 5 is exponential, based on powers of 2 (i.e., LAL 3 indicates twice the amount of lightning of LAL 2). LAL 6 is a special category for dry lightning (see description below) and is closely equivalent to LAL 3 in strike frequency.

 

The Lightning Activity Level on a scale of 1 to 6 as described below:

LAL 1: No thunderstorm or building cumulus clouds observed.

LAL 2: A single or few building cumulus clouds with only an occasional one reaching thunderstorm intensity observed. Thunderstorms or lightning need not be observed for this activity level to be assigned; however at least one large cumulus cloud must be present.

LAL 3: Occasional lightning (an average of 1 to 2 cloud-to-ground strikes per minute) is observed. Building cumulus clouds are common; thunderstorms are widely scattered.

LAL 4: Frequent lighting (an average of 2 to 3 cloud-to-ground strikes per minute) is observed. Thunderstorms are common and cover 10 to 30 percent of the sky. Lightning is primarily of the cloud-to-cloud type but cloud-to-ground lightning may be observed.

LAL 5: Frequent and intense lightning (cloud-to-ground strikes greater than 3 per minute) is observed. Thunderstorms are common, occasionally obscuring the sky. Moderate to heavy rain usually precedes and follow the lightning activity. Lightning of all kinds (cloud-to-cloud, in-cloud and cloud-to-ground) is characteristically persistent during the storm period.

LAL 6: A dry lightning situation. Low lightning flash rate observed (less than one to three cloud-to-ground strikes per 5-minute period per storm cell passage). Scattered towering clouds with a few thunderstorms; bases of the clouds are high. Virga is the predominate form of precipitation.

 

National Wildfire Coordinating Group

http://www.nwcg.gov/term/glossary/lightning-activity-level-(lal)