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How Do Wildfires Start?

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How Do Wildfires Start?
(Photo : Pixabay)

It is an unfortunate fact that the vast majority of wildfires in this country are triggered by the actions of humans. In fact, during the period between 1992 to 2012, there were 1.5 million wildfires triggered and 84% of those were caused by humans, with the remaining 16% mostly attributable to lightning strikes. These figures from the National Academy of Sciences make it clear that humans play a huge role in the starting of wildfires and once begun, the wildfires are perfectly capable of sustaining themselves and spreading. So what exactly causes a mere spark or burning ember to blaze into something as massive and dangerous as a wildfire?

How do forest fires start?

Each year, wildfires seem to burn hotter and consume more acreage than the previous year, although much depends on specific weather conditions from one year to the next. It is known that wildfires are triggered by having three prime ingredients present at the same time: heat, fuel, and oxygen. Since oxygen is always present in the atmosphere, only fuel and heat are needed to trigger a wildfire. Fuel is generally always available in large quantities as well, since grass, trees, brush, and even buildings are very suitable as fuel for a wildfire.

The dryer this fuel becomes, the easier it is to burn and the more likely it is to provide a good source for a wildfire. Heat is of course the final component and it's responsible for burning up that fuel and spreading to the surrounding area to increase a fire's overall impact. When these three components are all in place at the same time, it becomes a wildfire just waiting to happen and in many Western states of this country, it does happen; quite frequently and quite intensely.

In order for a spark to become a full-blown wildfire, it's generally necessary to have dry conditions in the area over a period of time and strong winds capable of spreading the fire on that particular day. Climate change is having an impact on this, since drier conditions are becoming more prevalent in Western states, so all that's needed is a strong wind to facilitate the spread of a wildfire.

Statistics show, for instance, that in California, Novembers were typically wet 50 years ago and that had a limiting effect on wildfires. However, the November of 2018 was so dry that it triggered the most destructive fire in state history and the same scenario is playing out in other states as well. In many cases, wildfires which are triggered by humans are not due to intentional acts of arson, but are simply related to human activities.

For instance, the most destructive wildfire in California history was sparked by a faulty electrical transmission line owned by the Pacific Gas & Electric Company. When the fire was finally contained, it had destroyed most of the town of Paradise, killed nearly 100 people, and had consumed almost 14,000 homes. The malfunction occurred near a very windy canyon, on a dry hillside, and so the wildfire spread quickly and raged out of control.

Power lines are actually a fairly common cause of wildfires and have triggered many blazes in California. Another very deadly fire in the state was triggered when a tractor-trailer with a flat tire produced sparks when it came into contact with the pavement. Since conditions were very dry and hot at the time, those sparks easily spread to vegetation by the roadside and were quickly pushed by strong winds across a very broad area. That wildfire consumed more than 1,600 homes and other buildings; resulting in the deaths of eight people.

There are other relatively unusual causes of wildfires sparked by humans, such as the sparks from lawnmower blades or weed whackers which come into contact with rocks. Even vehicle collisions can produce sparks and fires that can spread to surrounding vegetation and develop into a major conflagration. In 2007, sparks emitted by a metal grinder were able to leap into dry grass nearby and trigger a huge fire in Santa Barbara County and ended up being one of the biggest wildfires in California state history.

Hot components on the underside of an automobile can trigger a wildfire, too, if the vehicle happens to be parked over very dry brush. This is not something that a person would ordinarily think about, but when conditions are so dry, it takes very little to generate the heat necessary to trigger a wildfire.

Although an estimated 84% of wildfires are started by humans, arson is one of the rarest causes. A spectacular wildfire was triggered in the San Jacinto Mountains in 2006 by an arsonist, but this was a relatively rare case and the number of wildfires triggered by humans is generally attributable to other kinds of actions.

Learning how to prepare for a wildfire can help you protect your family and property in the event of an emergency.

How do wildfires spread?

Once a wildfire has started, it takes very little for it to be spread over a vast area nearby. One of the prime ingredients necessary to spread a wildfire is strong winds and when these are present, huge tracts of land can be burned up very quickly. When a wildfire is burning through a forest, it can move at a rate of up to six miles per hour when pushed by a strong wind and up to 14 miles when in a grassland.

When there's even a slight upslope involved with the terrain, it can speed up the rate of fire consumption dramatically. An extra 10 degrees of upslope can cause the speed of a wildfire to double, so any more slope can allow a wildfire to quite literally race upwards and forwards to consume vast amounts of vegetation.

It's also possible for a wildfire to leap across cleared areas or natural firebreaks such as streams, lakes, and rivers. High-standing shrubbery such as trees can have their burning leaves and twigs carried by the wind across these natural breaks to the other side; where they can then ignite vegetation there. Anything that is easily flammable will catch with an ember that passes over a natural firebreak, thereby propagating the wildfire.

Is there any way to prevent wildfires?

Despite the inevitable wildfires that occur each wildfire season, there are some steps that can be taken by humans to reduce the frequency of them. For one thing, setting off fireworks should be avoided entirely, since they are capable of providing exactly the kind of spark needed to trigger a wildfire.

The same is true of discarding used-up smoking materials like cigarettes or matches, because they provide the necessary heat source, too. Campfires should never be left unattended, since it's very easy for an ember to go flying off into the air and ignite nearby vegetation. It's also best not to do yard work after mid-morning, because a spark from a lawnmower or weed whacker might accidentally spread to dry vegetation and trigger a wildfire.

Even driving your vehicle over brush or grass that is extremely dry can supply enough heat to trigger a wildfire, so you should avoid passing over grassy areas. Finally, you should never leave candles burning unattended so that they have a chance to burn all the way to the bottom. If there happens to be any flammable material close by, they could easily be ignited and flames could spread throughout the building and beyond.

Closing Thoughts

It takes very little to start a wildfire, since all that's needed are heat, fuel, and oxygen. If a good, strong wind is present, any fire will spread quickly, potentially over a very large area. That makes it important for humans to be very conscious of the fact that wildfires are easily triggered and spread and to do everything possible to avoid sparking a blaze. This is especially important now, given that weather conditions in recent years have allowed many areas to become hotter and drier than ever before and are far more susceptible to damage. Be careful and stay alert!

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