7 Reasons Lawnmowers Catch Fire

Approx Reading Time: 13 minutes

In this blog post, I will discuss the most common reasons for why lawnmowers catch fire. I will also share some tips and tricks on how to prevent your lawnmower from catching fire.

Scroll on to read the detailed reasons and prevention methods.

1. Fuel Hazards are one of the leading reasons for fire in the gas-powered lawnmower:

One of the most common causes of lawnmower fires is when you refill fuel or oil into a very hot engine that has long been in use. Its muffler is able to ignite the vapors and set your lawnmower on fire. You must refill the gas and check the oil level before you start mowing the grass.

If you run out of gas while mowing the grass, before refilling it, let the mower sit and cool at least for half an hour. After refilling the fuel or oil, wipe up any spills. Never store the gasoline container anywhere near the lawnmower.

Never light a cigarette while refilling the fuel or oil into your lawnmower. Make sure your mower is stored away from your outdoor grill.

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2. Lawnmowers catch fire when dry grass gets stuck in the mower deck:

Your lawnmower can catch fire when the weather conditions are blazing hot. When the grass is dry it gets packed in your mower deck, which increases the risk of catching fire. When the dry grass builds up in your mower deck, it goes into its muffler, which can catch fire, then fall out and set a whole field on fire.

Fire experts recommend wetting the area if you are about to mow dry grass or brush on a hot sunny day. It is also recommended to mow early in the morning when the humidity level is higher. It is a good idea to avoid mowing on dry, hot and windy days.

Start mowing around your house and work to create a barrier if you are mowing in dry and hot weather conditions conducive to fire. This way, you can prevent fire since a barrier has been created. It is also a good idea to service your lawnmower in the spring, early summer, fall or in between, as the temperature and humidity level is favorable enough to prevent fires.

3. Lawnmowers catch fire when its metal blades strike rocks:

The blade of your lawnmower is moving at two hundred miles per hour if it strikes against a rock or a stump of a tree, it will cause a spark and ignite dried grass. Moreover, the blade can itself come flying off, this can be life-threatening.

There are five things you must always avoid, otherwise, the blades of your lawnmower become dangerous. i) If you sharpen the blades of your lawnmower too many times, they become thin, worn out and weak. If you accidentally hit them against a rock or a tree stump, the blades will come off and injure you.

ii) If the blades of your lawnmower are bent, they will be out of balance. They will scalp your lawn and damage your bearings.

iii) If the blades of your lawnmower are broken, they are at the risk of completely breaking off and injuring you. They are also out of balance and will probably ruin your bearings.

iv) If the blades of your lawnmower are cracked, they can come flying off if you unintentionally hit a rock or tree stump, causing property damage or injuring you.

v) If you alter your lawnmower blades and ignore the strict safety standards observed by the manufacturer, you are at the risk of personal injury, property damage, and even death.

4. Another primary reason for lawnmower fires is due to the grass being left to grow far too high:

High grass creates clippings and particles that will fly up over the deck of your lawnmower and come in contact with its hottest parts such as the muffler. They can enter the cooling fans and make their way into the hottest parts of its engine causing an ignition. Field grass is entirely different from your lawn grass.

Field grass will grow faster and higher, even higher than your lawnmower deck. It becomes dry only at the top, while your lawn grass stops growing any higher when it dries out in extreme weather conditions. If you let your field grass grow too high, you must seek professional assistance to mow it to prevent a fire.

“A standard lawnmower is not meant for mowing fields,” said Haddam Fire Chief Sam Baber. “Dry grass builds up in the lawnmower deck and gets in its muffler where it can catch fire, fall out and set a whole field on fire.” If not used correctly, Baber added, a push lawnmower is just as dangerous as a riding lawnmower.

“If you have high blades of grass, and a fire is just starting and burning right next to the ground, it will burn the bottom of the grass off first and grass stems will fall toward the flames,” said Mr. Jon Skinner, who oversees fire investigation and recovery for the federal Bureau of Land Management. “But if the fire is ripping through that grass, it will burn the tops of that grass first.”

5. Fuel vapors around a hot muffler can catch fire:

The fuel vapors get packed into the blazing hot muffler and catch fire. “The biggest tip is to make sure you turn it off and let it cool for at least two to three minutes,” Springfield Fire Department Captain Paul Byers said. “Gasoline has a very low flash point and the engine is hotter than that flashpoint and if you are pouring in and you actually splash it onto the muffler or the head of the engine, it is enough to ignite it and cause a fire right there.”

Even after hours of your lawnmower being turned off, its heat sensor shows the muffler temperature near two hundred degrees. The engine of your lawnmower generates a lot of heat. If the engine cannot properly dissipate that heat it is at risk of bursting into flames.

Your lawnmower engine has cooling fins molded into the block. Clippings of grass, dust, and debris can clog its fins and act like a blanket, holding too much heat close to the engine. The plastic housing or shroud that covers the top of your lawnmower can also trap a lot of dust, enough to overheat the engine.

6. A gas cap leak or sloppy fueling can easily start a fire:

The most likely cause of overheating in your lawnmower engine is a leaky gasket in its carburetor. A leaky gasket has the same effects as a lean fuel-air mix. A leaky gasket will create a gap that lets fuel in and air out, leading to a lean mix.

“The dirty air filter will make an engine struggle even harder, it does not get the air it needs to go through and it will run hotter than necessary,” Captain Byers said. “The oil being low can also create a really overheat condition.” Fuel leaking onto the motor can catch fire.

If you accidentally spill some gasoline on the grass, don’t mow that patch of grass until all of the fuel has dried away, as the engine or muffler can ignite it. Always refuel on a hard floor. Place a plastic container underneath to collect any spillover.

Air leaks cause the engine of your lawnmower to pull in too much outside air. This throws off the gasoline to air ratio. When the engine overheats, its parts expand, and all small gaps become large.

The lawnmower fuel line can easily detach from the plastic fuel tank outlet, resulting in serious risk of a fire. To avoid this from happening, you must use replacement fuel tank outlets that are redesigned with large barbs intended to hold the fuel line more securely. 

7. A short in the circuit board can start a fire:

A short circuit is an abnormal connection between two nodes of an electric circuit that are intended to be at different voltages. This results in circuit damage, explosion or outbreak of fire. A common type of short circuit occurs when the positive and the negative terminals of a battery are connected with a low-resistance conductor, like a wire.

In riding or push lawnmower unintentional short circuits are usually caused when the insulation of wire breaks down, or when another conducting material is introduced, allowing charge to flow along a different path than the one intended. When a damaged choke inside the carburetor of your electric lawnmower stays closed instead of opening even after its engine starts, this results in a flooded engine that badly needs a little air to breathe. Some lawnmower carburetors have an electronic solenoid that helps in its operation.

If your lawnmower’s solenoid has gone bad, then its engine will get overheated, ultimately resulting in flames. Lawnmower engines can be difficult to diagnose when it comes to temperature. You must pay special attention to the temperature monitoring gauge to avoid catastrophic engine combustion.

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How to prevent lawnmowers from catching fire?

Fire Chief Mike Harris said you need to be prepared before heading out, even if your Spring Cleanup does not involve a controlled burn. “You must build a firebreak, have water available, keep your piles small, and watch for the wind,” Harris advised. “It does not take much to carry a small, controlled-burn through vegetation. We see it every year.”

To prevent overheating, you must keep the engine of your lawnmower clean and tidy. Dust, dirt, debris and dry grass can get into its vents and block the air intake which means that cool air cannot flow to the engine and cool it. You must regularly take off the casing of your lawnmower and dust off all the dust, dirt, debris and dry grass that has built up inside it.

You must make use of blasts of compressed air, a toothbrush, and a vacuum cleaner to knock off the stubborn, sticky debris, bird droppings, etc. If you are lazy enough to skip this necessary maintenance, then you must seek the assistance of a professional mechanic to do it on a regular basis for you.

The next step to prevent your lawnmower from catching fire is to check its oil level. A critically low oil level means that the lubricant is not circulating through the lawnmower engine properly, meaning that a lot of friction is being created and the result of friction is heating. To prevent the friction from bursting into flames, you must shut down the engine, disconnect the spark plug, then let the engine cool down for at least half an hour, now you can add enough oil to bring the level up to a sufficient and safe point.

Another most important step to prevent your lawnmower from catching fire is to check the cooling fins and shroud for any damage. Both the cooling fins and shroud are meant to dissipate the heat from the engine and into the airstream. If there are any cracks in your cooling fins or shroud, they will not be able to remove the heat away from the engine, ultimately increasing the danger of your lawnmower catching fire.

The next step is to check your fuel-air mixture. If the mix is lean, it means there is more air than normal in the combustion chamber of your lawnmower. More air translates to the detonation of the fuel instead of its combustion which creates too much heat. You can fix this by adjusting your carburetor for a mix that is heavier on fuel.

To prevent your lawnmower from catching fire you must:

  • Check its oil level after five hours of use.
  • Change the oil after fifty hours of use.
  • Replace the oil foam after twenty-five hours of use.
  • Replace the inline fuel filter after fifty hours of use.
  • Replace the spark plug after a hundred hours of use.
  • Clean the cooling system after a hundred hours of use.
  • Clean the combustion chamber after one hundred to three hundred hours of use.
  • Inspect the spark arrester after fifty hours of use.

Fifteen things you should NEVER do:

  • Never point the lawnmower discharge chute towards your home, kids, pets, street, structures or vehicles.
  • Never allow an extra rider on your riding lawnmower.
  • Never mow with a riding lawnmower in reverse direction unless absolutely necessary.
  • Never leave a running lawnmower unattended.
  • Never alter, bypass, disconnect, tamper or remove any safety controls.
  • Never tilt a walk-behind lawnmower, make sure you keep all of its four wheels on the ground.
  • Never use an electric lawnmower during rain or to mow wet grass.
  • Never use a frayed extension cord.
  • Never put your hands or feet under the deck of your lawnmower.
  • Never allow your children or pets to come outside on the lawn while you are mowing the grass. Never assume that children will stay where you last saw them.
  • Never refuel the gas tank indoors or store your gasoline container indoors. Never add more fuel than you can use within two weeks.
  • Never store your lawnmower or gasoline container near an open flame, the pilot light of a water boiler or spark.
  • Never refill your gasoline containers on your truck bed with a plastic bed liner or inside any vehicle.
  • Never remove the gas cap or add fuel while the engine of your lawnmower is still running. Never over-fill its fuel tank.
  • Never pull off the road into the brush or dry grass with your riding lawnmower as its hot exhaust pipes and muffler will catch fire.

Five things you should ALWAYS do:

  • Always read, understand and follow all the safety instructions given in your user’s manual.
  • Always store your gasoline in a sealed container with a CSA, FM or UL label.
  • Always make sure you have a properly working spark arrester on your gasoline-powered lawnmower.
  • Always keep a cell phone handy.
  • Always place the gasoline container on the ground away from your vehicles before filling.

Conclusion

To conclude this blog post, I would say that accidents and fires occur when the operator of the lawnmower is inattentive and careless. If you read, understand, remember and follow all the safety instructions provided by the manufacturer of your lawnmower, you will never face a disastrous fire. To keep yourself, your loved ones and your precious property safe and secure, you must always be very careful and extra attentive while operating any kind of lawnmower.