Southern California has a lot of two things – vehicles and wildfires. We have often seen conflagrations attributed to a mere spark from a tailpipe. But how does that actually happen? Let’s break down the process:

Step 1: Generation of hot particles

Sparks coming out from a gas or diesel vehicle tailpipe are hot carbon particles created by an engine. How are these made? By a process called combustion, when fuel and air burn to power the vehicle. Thankfully, sparks from a tailpipe rarely happen, since most vehicles are equipped with a spark arrester, preventing sparks from exiting the tailpipe. But that’s not the only way that sparks can be produced unintentionally by a vehicle…

Sparks also can be produced by metallic friction. Imagine a metallic chain slightly hanging from a trailer or tow truck, long enough to touch the road. When the vehicle starts moving, the contact between the chain and the floor could produce sparks. In this case, the sparks would be hot metallic particles.

Either way, these hot particles – sparks – would not fall directly on the floor at the same position as they were created. They would fly. Which leads us to Step 2.

Step 2: Flight of hot particles

Hot particles fly either by the wind, by the velocity they had when they were created, or both. During flight, particles get colder. The longer the flight, the colder the particle becomes. Clearance distances along highways are helpful to allow hot particles to lose temperature and, therefore, avoid starting fires. However, winds like Santa Anas might cause particles to move long distances faster, making them land when they are still at a hot temperature. And that’s when Step 3 occurs.

Step 3: Ignition after the particle landing

The starting to burn process is called ignition, which is a very complex process. Researchers at UC Berkeley have demonstrated that it mostly depends on three things: How the particle loses its heat; how the place where the particle lands is heated by that hot particle; and the sort of reaction between the particle and the landing place. Depending on these three factors, either smoke or flames will happen.

Step 4: Fire start and generation of embers

If flames occur, they will start burning vegetation and trees, creating embers in their wake. If not controlled, Step 5 will rapidly occur: Wildfire.

Step 5: Embers spreading the fire

Embers are other kinds of hot particles that ignite a fire. They can be carried relatively long distances by wind. When a wildfire is on, embers can be moved to spots much farther from the first ignition zone. That’s called fire spotting, which is more difficult to predict, leading to a more rapid fire spread. Imagine the following situation: a highway crossing a forest where one side is burning and the other isn’t. An ember could be brought to the other side of the drive, starting a fire on the side that was not burning.

So, let’s act before Step 5! Regularly check your car, including with a mechanic, and make any necessary repairs. Also, report possible spark hazards, such as vehicles with metallic pieces touching the ground. The sooner, the better to still enjoy road trips to the wilderness.