An ATV spark arrestor is a necessary component of all ATVs made in the USA. They are required in order to ride in most public riding areas.
Years ago when off-road vehicles used to cruise through the woods, they did so with knowledge that any engine misfire could result in sparks escaping the exhaust system. In most cases a puff of fire coming out of the muffler was not a problem.
During the 1980s---when ATVs started riding through the woods in higher numbers---there was a fear that a small puff of fire escaping an exhaust pipe would result in a forest fire. This was especially a concern in the Southern California area, where wildfires can be highly problematic.
US Forest Service
With the number of ATVs growing, the U.S. Forest service launched a campaign to force all ATV manufacturers to include a spark arrestor in the muffler of any ATV sold in the United States. For a short time, people could purchase aftermarket exhaust systems for their ATV that did not have a spark arrestor. Many people felt that the newly inserted piece of material was slowing their ATV down. But as time wore on, the aftermarkets, too, would be forced to comply with the new rules.
Where are they?
The spark arrestor is located at the end of the muffler assembly. It is designed to resist collection of ash or other combustible materials.
What are they made of?
In general a spark arrestor is made of woven steel wire, similar to a screen. Its usually shaped like a cone and placed with the apex of the cone pointing in. This cone is designed to dissipate any spark or fire that does try to escape the muffler by breaking it up.