Introduction to Spark Arrestors
Ralph H. Gonzales, Mechanical Engineer
The United States Department of Agriculture (USDA) Forest Service effort in combating equipment-related fires started in the 1920s with external combustion engines (steam donkeys) used in logging.
In the early 1950s, the USDA
Forest Service became interested in reducing the number of fires caused
by internal combustion powered logging equipment. This effort was based
on the 1934 report by J.P. Fairbanks and Roy Bainer entitled “Spark
Arresters for Motorized Equipment,” published by the University
of California at Berkeley. The research demonstrated that exhaust particles
with a diameter of 0.023 in or larger were responsible for the majority
of fire ignitions.
In April 1968 the Society of Automotive Engineers (SAE) in conjunction with the USDA Forest Service and small-engine manufacturers published the SAE Standard J335. It set the standard for small engines (chain saws, string trimmers, etc.) that not only prohibits the escape of carbon particles greater than 0.023 in but also regulates the allowable temperatures of the exhaust gases and the surface temperature of the exhaust system. The USDA Forest Service Specification 5100-1 defines performance specifications for spark arrester exhaust systems used on general-purpose engines (generators, motorcycles, agricultural equipment, etc.).
Currently, a significant number of States, municipalities, federally managed lands, and all USDA Forest Service regions require that all internal or external combustion engines must be equipped with a spark arrester that meets the requirements established by the SAE Standard J335 or USDA Forest Service Specification 5100-1. The Code of Federal Regulations, 36 CFR 261.52, and orders written by USDA Forest Service line officers explain the requirements.
and the Internal Combustion Engine
The condition of an engine, or how well it is tuned, can affect its ability to start a fire due to the temperature of its exhaust and the size and amount of carbon particles it produces. The type and quality of gas and oil, and the mix ratio can affect the size and composition of exhaust particles. The design and location of the exhaust system itself can greatly affect whether a piece of equipment will start a wildland fire. The temperature, humidity, and density all contribute to how well the wildland fuels will burn.
The GP spark arresters are designed for use on engines in a single position, such as tractors, motorcycles, or railroad locomotives. There are a variety of spark arrester designs for general-purpose engines. The most common types are the trap, screen, and disc.
Spark Arresters Work
Superchargers, and Mufflers
Superchargers do not use the exhaust gas but are directly coupled to the engine. Engines equipped with superchargers require a spark arrester.
Mufflers are designed to reduce the noise emitted by the engine and are not considered effective spark arresters. Catalytic converters are not considered effective spark arresters either. They can reach temperatures high enough to start fires through contact with dry vegetation. There are several MSE spark arresters that have a catalytic element to reduce harmful emissions. These spark arresters have been tested according to the SAE J335 and are qualified.
and Maintenance, Who is Responsible?
Arrester or Muffler, How To Tell the Difference?
There are two volumes to 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.
Attn: Spark Arrester Program Leader or http://www.fsweb.sdtdc.wo.fs.fed.us
Project Leader, Fire Management
San Dimas Technology & Development Center
444 East Bonita Avenue, San Dimas CA 91773-3198
Phone 909-599-1267; TDD: 909-599-2357; FAX: 909-592-2309
Information contained in this document has been developed for the guidance of employees of the Forest Service, United States Department of Agriculture (USDA), its contractors, and cooperating Federal and State agencies. The USDA assumes no responsibility for the interpretation or use of this information by other than its own employees. The use of trade, firm, or corporation names is for the information and convenience of the reader. Such use does not constitute an official evaluation, conclusion, recommendation, endorsement, or approval of any product or service to the exclusion of others that may be suitable.
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