Off-Highway Vehicle Spark Arrestors
SPARK ARRESTERS AND THE PREVENTION OF WILDLAND FIRES

Ralph H. Gonzales, Mechanical Engineer

• History
• How Spark Arresters Work
• Qualifications for OHV Spark Arresters
• Spark Arrester Inspection
• Exhaust System Maintenance
• Summary
• Spark Arrester Guide
• Additional Information

Spark arrester laws vary from State to State. OHV operators should consult their State’s policy.

The following are some of the most commonly used OHVs that require spark arresters.
ATVs: They are usually less than 54-in wide and weigh less than 650 lb. They have three or more flotation tires, are steered with handlebars, and are operated in a straddled riding position. All ATVs sold in the United States have spark arresters as part of the original factory equipment.

Motocross Bikes:
These are designed for closed course competition. Generally, they come equipped with a muffler/silencer, which is not a spark arrester. They do not have a headlight or a taillight. Clues to defining a motocross bike are numbered plates, radiators on later models, two-stroke engines, and travel in the suspension that causes them to sit high.

It should be noted that motocross motorcycles are very popular among competitors and serious trail riders. This is an acceptable bike on many public jurisdictions providing it is equipped with an approved spark arrester and silencer/muffler.

Enduro Motorcycles:
These motorcycles come factory equipped with a spark arrester. They are legal for use on public lands and are easier to inspect than motocross motorcycles. Enduro motorcycles are designed for OHV routes, desert riding, trail riding, and general off-road use. Most come equipped with approved spark arresters and small headlights and taillights.

Dual-Purpose Motorcycles:
These are designed for on- and off-highway use, but must also meet all requirements for public highways. Headlights, taillights, brake lights, and turn signals are required.

Volkswagen (VW) Dune Buggies: The VWs are required to have a qualified spark arrester for off-highway use. Some dune buggies are street legal, have a license plate, and usually have a muffler. Mufflers are legal for street use, but do not qualify as a spark arrester for off-road use.

Dune Buggies:
Dune buggies are built for off-road use only. While some are equipped with spark arresters, many can be identified by a straight exhaust that is very noisy and lacks a spark arrester.

How Spark Arresters Work
Spark arresters work on the principle of trapping or pulverizing carbon particles with a diameter greater than 0.023 in. The centrifugal trap-type arrester is by far the most common design used by OHV enthusiasts. In addition to the requirement of certain efficiency levels, a trap unit must have a clean-out device.

Various methods are used to clean accumulated carbon particles out of a spark arrester. Some include a cleanout plug, end cap, cleanout plate, inserts, snap rings, cleanout bands, and Allen bolts. The spark arrester must be serviceable without removing the complete exhaust system.

The cleanout requirement is one of the most critical elements of the trap arrester. It is also one of the most often ignored. During inspections, owners must be reminded that this type of arrester requires regular and timely maintenance, a critical element of spark arrester effectiveness.

Some models of spark arresters/mufflers require fiberglass packing. This packing should be replaced every 30 hours. Evidence of exhausted packing includes oil dripping from the exhaust tail pipe and/or excessive noise. Fiberglass is the only approved qualified packing.

Qualifications for OHV Spark Arresters
The qualification standard requires spark arresters to be permanently marked with the model number and manufacturer’s name or trademark. Whenever contact is made with an OHV, regardless of what type of machine is used, a spark arrester inspection should be made.

Many people think that a muffler/silencer is also a spark arrester. Mufflers and silencers are only designed for noise control. Only an inspection can determine whether this is a spark arrester or a muffler/silencer.

If the OHV has been operating, beware of very hot metal in and around the exhaust system. The arrester will be a chamber-like device located somewhere along the exhaust discharge. Find the manufacturer’s name or logo and the model number located on the spark arrester. It may be necessary to clean a portion of the arrester to reveal that information. It can usually be found on an attached metal plate. The words “USDA Forest Service Qualified,” “Spark Arrester,” or “Qualified” stamped on a piece of equipment does not guarantee that it is a tested and qualified arrester.

Spark Arrester Inspection
Check to see if the entire exhaust system is sound and the arrester has been maintained. Also make sure that the spark arrester is mounted securely in the qualified position. In OHV use, this is usually the horizontal position. Proceed with a thorough inspection of the entire exhaust system.

With the engine off, and using a penlight, look into the spark arrester to visually ensure that the interior has not been removed or altered. You may be able to see the interior section that deflects the exhaust. Use a narrow rod, such as a 8-in wooden dowel, to gently feel for the internal parts of the arrester. Check how far you are able to insert the wooden dowel internally and cross check this measurement with the outside of the spark arrester/muffler. This will indicate whether you are able to pass the dowel the length of the arrester/muffler. If you are able to pass the dowel the total length, it is not a qualified arrester.

All trap spark arresters have internal fins or louvers that deflect the exhaust. If you suspect that an arrester may be altered, have the owner take the arrester apart for further inspection. Although the arrester/muffler may have the approved model number and the manufacturer information stamped on the shell, the inside components of the spark arrester mechanism may have been removed. Only through a thorough inspection can this type of modification be noted.

Arresters can be modified to avoid routine maintenance or to give the false perception of improved engine performance. Some modifications that have been detected include complete or partial removal of the spark arrester component parts, perforation of an arrester part, and installation of foreign objects into a muffler silencer, “mocking” spark arrester parts when a wooden dowel probe is used. Examples of these foreign objects are washers, bottle caps, and steel wool.

Exhaust System Maintenance
The next step is to check the exhaust system for maintenance. The exhaust system must be without holes, gaps, loose connections, or any areas that exhaust can escape without passing through the spark arrester. If the integrity of the whole system is not complete, the piece of equipment cannot pass the inspection regardless of whether it has a qualified arrester or not.

Owners must be aware that spark arrester laws include the term “in effective working order.” Spark arresters need to be periodically cleaned to eliminate the trapped particles of carbon. The same conditions that cause spark plugs to foul can also cause a spark arrester to become inefficient. If it is not maintained, then its performance is hampered and it is not considered a legal spark arrester.

Summary
As you become more informed about spark arrester inspections, you will look forward to educating OHV enthusiasts about the proper use and maintenance of spark arresters. The use and maintenance of spark arresters can contribute to the effort of preventing unwanted wildland fires.

Spark Arrester Guide
The Spark Arrester Guide is the only authoritative industry source for information on qualified spark arresters for use on internal combustion engines. Use the guide when identifying qualified spark arresters. If the spark arrester number appears in the guide, SDTDC has evaluated the arrester.

There are two volumes of the guide: General Purpose and Locomotive, Volume 1, and Multiposition Small Engine, Volume 2. A revision of the guide is published every year. Therefore, each volume is published every 2 years. An online guide, updated every quarter, is available on the USDA Forest Service Intranet at http://www.fsweb.sdtdc.wo.fs.fed.us. It is a searchable database that allows the user to make powerful searches.

Additional Information
This Tech Tip offers a broad introduction on OHV spark arresters. There are four other Tech Tips in the series. For more information on spark arresters, or to receive copies of other related Tech Tips, contact:

USDA Forest Service
San Dimas Technology and Development Center
444 East Bonita Ave.
San Dimas, CA 91773

Attn: Spark Arrester Program Leader or http://www.fsweb.sdtdc.wo.fs.fed.us

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