Fire, an Amazing Phenomenon

While we watch and wait while the Brown Fire (burning near my community) continues to burn, I began to wonder about fire and decided to do a bit of research.  (See my blog, “On Edge – Again.)  At nighttime, when we look toward the fire, it is a beautiful sight, but at the same time frightening.  It really is an amazing phenomenon. 

Here are a few things I learned about fires.

A fire requires three elements to exist:  a Heat source, a Fuel source, and an Oxygen source. (I learned that in grammar school.) When these three elements come together, a chain reaction occurs, oxidization (combustion).

Once a fire begins, it produces its own heat and draws air into the fire. As the temperature rises, other materials may reach their ignition temperature and become fuel for the fire.  In this way, the chain reaction continues.  It will continue until one of the elements is removed (cooled, starved, or smothered).

When weather conditions are dry and hot enough, brushfires and wildfires, the conditions prepare the fuel (trees, brush, leaf litter, etc.) so it will burn readily.  Fires may be caused by a natural (e.g. lightning) or be man-made (e.g. discarded cigarette) source.  It has been determined that the one burning in my area was man-made as was the one in 2011.

A wild fire can create its own weather system. A large amount of rising heat and air causes more air to be drawn into the fire, and can create a rising vortex which builds upon itself, growing bigger and stronger. They can jump around and change direction just like a regular storm tornado. They can occur at a large structure fire also.

If a fire gets big enough, it can heat up the air in the center of the fire so hot and quickly that it sucks in more air along the ground.  As the amount of air being sucked in increases, the wind increases, further drying out the fuel along the perimeter of the fires.  In extreme cases, it can actually suck in fuel.  As more air is drawn in, more oxygen is available for the fire to continue and grow in size.

At this point, the fire becomes self-sustaining and will stop only when it runs out of flammable fuel, or if people are able to stop it.  These large, uncontrollable fires most often occur in the more arid areas of the United States and other countries where rainfall averages are very low. In areas such as these, the weather is naturally dry with very low dew points.  Combining drought conditions with all of the other naturally occurring factors, a single spark could ignite a fire.

Wild fires and brush fires are difficult to stop, because firefighters usually cannot get enough water to cool the fire below its ignition temperature.  In addition, as I mentioned above, brush fires create their own weather as they grow in size, causing the air around them to become super-heated, preventing the water used by the firefighters from cooling it down enough to be extinguished.   In fact, the ground floor may harbor the heat and embers keeping the fire alive.   

Most wild land firefighters form fire breaks in the land, allowing the fire to burn itself out.  With structural fires, firefighters try to protect exposures such as homes against any embers flying around.

Reading and learning more about fires makes me appreciate the many brave firefighters even more than I already did.  When everyone else is running FROM a fire, they are running toward it.

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