home page archives

april 2008 home page

Tackling the “Fire Triangle”
April 2008 | by Dismas Abelman

Let's make this a thing of the past.

The City of Del Mar, in cooperation with the San Diego Museum of Natural History conducted the seminar “Living with Wildfire”. This seminar held on March 12 at the City Hall Annex was in response to a heightened awareness by community members since the most recent wildfires in October of 2007. Members of the Natural History Museum and the Del Mar Fire Department presented together a broad range of expertise on the subject of fire and the Southern California environment. Here are the highlights about the dangers of wildfires.

Fire is the rapid oxidation of a fuel resulting in heat and light production. In order to have a fire, three materials are needed: a source of ignition, fuel and oxygen. This combination of materials is called the fire triangle. The fire triangle is critically important to southern California residents because oftentimes our homes or the vegetation near us is the fuel in the triangle. The goal is to minimize the fuel in the event of a wildfire, or place it in a configuration that is less likely to burn. Knowing this, it is then essential to understand the development of the basics of fire behavior. Given a set of circumstances, fire will burn in a predictable manner. The object of fire prevention is to develop a set a circumstances that are less likely to lead to fire, and if a fire occurs, to minimize the potential for damage. This could result in fewer lives lost and less property destroyed in a large wildfire.

Many people are aware that most large fires occur when the Santa Ana winds impact Southern California. Weather is only one factor that dictates the intensity with which a fire will burn. Weather, fuel and topography are the main factors that will cause a fire to burn with tremendous heat at a rapid rate of speed or slowly with little heat or intensity. The Santa Ana winds have a drying effect on the fuels, assisting vegetation in getting started easily and allowing fire to spread rapidly. The winds have the added detrimental effects of fanning flames and making a fire line more difficult to contain and carrying embers to other places where fuel exists.

Another weather impact can be prolonged drought, which causes the drying of fuels in the area. That is, the fuels actually have less moisture contained in the branches and leaves, which allow for easier fire starts and rapid fire spread. It can also stress and kill the plants of an area increasing the amount of fuel to burn. Once the fuel has died, no amount of rain will bring it back to life, so a good rainy season or a couple of good rainy seasons will only increase the moisture levels on live plants and not provide any help to the dead fuels. Once the weather starts to dry out, the fire danger will return.

The topography will affect the way a fire burns once it gets started. It is important to remember that a house or a road built at the top or halfway up a hill will have to withstand a fire burning with greater intensity than a fire under the same conditions on flat ground. If a house is at the top of a hill on top of a draw (usually the best location for a view) the house will be exposed to a furnace if the fire gets into the draw. A draw is a canyon that runs from the bottom of the hill to the top.  This configuration allows both sides of the canyon to heat causing the flames to move up the draw, FAST.

Fuel is the final portion of the equation. Depending on where you live in San Diego County, you can have almost any type of fuel. On the coast we see a lot of scrub and chaparral. Although this type of fuel doesn't look like it poses much danger, it is important to remember that this fuel, under the right conditions, will start easily and spread quickly. Since fuel is the only factor we have the ability modify, it is important to take the steps available to reduce the likelihood of loss of life and property when a fire does occur.

The City of Del Mar is exploring the possibility of presenting the “Living with Wildfire” class again in the future. The scheduling will depend on the level of interest and schedule for interested participants. If you are interested in attending, please contact the fire department at 755-1522.

Dismas Abelman is Deputy Fire Chief and Fire Marshal for City of Del Mar and Solana Beach.


