The American Type 3 Brush Engine
A close look at the backbone fire engine in the Wildland Urban Interface / Intermix, examining advantages and disadvantages of this fire apparatus on which fire fighters
and communities depend on.
By Beverly B. Voelkelt, March 2012
Copyright © - B.O.R. Consulting
The standard American fire apparatus used in the wildland urban interface / intermix is a Type 3 brush fire engine utilizing a four wheel drive train and elevated chassis. It is considered a fire engine, not a fire truck, because it serves a dual purpose in its application – that of structure protection and wildland fire fighting.
The minimum required standard for Type 3 Brush Engines is defined by the National Fire Prevention Association (NFPA) in Standard 1901 and 1906. The National Wildfire Coordinating Group (NWCG) summarizes this standard in its handbook 410-1. Agencies, like Cal Fire, BLM and the U.S.F.S., and individual fire departments use the above listed standards to determine their one requirements on and configuration of a Type 3 Brush Engine. These may be Cal Fire’s model 34, BLM’s model 667 or the U.S.F.S models 326 or 346. At present, a very popular truck chassis used for Type 3 Brush Engines is the International Navistar, a basic cargo truck outfitted with four wheel drive. It is not a truck with a frame and suspension specifically designed for off-road use. One can understand and appreciate this concept because in most wildland urban interface conditions such a vehicle will suffice. However, there are many locations and situations that call for a more specialized Brush Engine.
Typically one finds Type 3 Brush Engines to feature a standard truck chassis with a four wheel drive train. They are powered by strong diesel engines and transmissions with power takeoff that drive onboard water pumps. They feature a typical wheelbase of 175” (444.5cm), higher ground clearance of 8” (20cm) minimum at the differential and 12” (30.5cm) minimum for the body. Of critical importance are the approach and departure angles for negotiating steep roads and rough terrain. The standard calls for a minimum approach angle of 28 degrees and departure angle of 17 degrees. They carry an onboard water supply of at least 500 gallons (1893 liters) and a pump with a minimum output of 150 gallons per minute at 250 psi (570 liters per minute at 1720 kPa). For hose packs the standard calls for 500’ (152m) of 1.5” (3.8cm) diameter hose and 500’ (152m) of 1.0” (2.5cm) rapid attack hose. Their staffing calls for a minimum of three firefighters. In crew cab configuration they may carry five firefighters. The typical purchase price for a Type 3 Brush Engine in 2006 was between $ 300,000 and $ 350,000.
In his lecture on the need for a “Holistic Framework to Sustainably Manage the Wildland Urban Interface“ at the fall opening webseminar series by the California Fire Science Consortium in September of 2011, professor Chris Dicus also addressed the subject of preparedness, emphasizing the need for “appropriate types and levels of suppression infrastructure, i.e. water, fire engines, etc”. Following Dr. Dicus’ thoughts, one observes that California’s foothill communities and the communities in the steep and rugged Sierra Nevada, San Bernardino Mountains and elsewhere require fire engines capable of handling the challenges of steep inclines and narrow, twisty roads. At the same time they must be able to deliver strong fire fighting attack capabilities, especially in communities that were established long before fire protection standards were developed. Many of these places have high housing density, little setback separating homes and inadequate fire flow (fire hydrant output) infrastructure, all in addition to being poorly accessible.
In this kind of wildland urban interface / intermix environment, city fire engines of the type 1 and type 2 are, for the most part, not practical at all. Even the standard Type 3 Brush Engine, as the ones pictured above, is not always an ideal design for some of the difficult conditions they encounter. In the San Bernardino Mountains, for example, there are many parts in communities this engine can not reach; thus cannot delivery its fire fighting capabilities. The long engine compartment with its forward axle design is old school and increases the turning radius of these engines significantly; thus making it difficult to negotiate narrow, single lane roads with tight curves. It also impairs the driver’s ability to see the road ahead, especially when driving up a steep slope. Their off-road capabilities are limited by their conventional suspension, lack of wheel travel, body flexibility and drive train design. After all, they are all constructed on a regular cargo truck chassis, not on a truck chassis specifically designed for off-road use.
Enter European Brush Engine designs. Manufacturers like Germany’s Mercedes-Benz with the world renowned Unimog or the M.A.N. company, and the Czech Republic’s Tatra; all with their incredible chassis designed specifically for off-road purposes, like forestry, dirt moving, civil defense, forest fires, etc. These trucks are Rally Race proven, winning grueling endurance and high speed races such as the Rally Paris – Dakar; an extremely demanding race that covers 5,150 miles (8,300 km) over the most difficult terrain imaginable in only 14 days ... http://www.wikipedia.org/wiki/Dakar_Rally . To give the reader a better impression of what is expected of these vehicles, here a few pictures of these extraordinary off-road trucks in action .....
When one combines such technologically advanced off-road truck designs with high caliber fire fighting technology and passive as well as active safety features, one ends up with a wildland urban interface / intermix Brush Engine that outperforms all competition.
Here, as just one example, the specifications of the Mercedes-Benz Unimog 2450 L 38 4x4 on the platform of the U-5000 series, the largest of the three Unimog platforms.
Length (bumper to bumper): 243.7 inches (6190cm)
Wheelbase: 155.6 inches (3850cm)
Height: 116.9 inches (2970cm)
Width: 92.1 inches (2340cm)
Turning Radius: 500.0 inches (12.7m)
Ground Clearance at Differential: 19.7 inches (50.0cm)
Approach angle: 48 degrees
Departure angle: 37 degrees
Hill climb: ascent – 45 degrees (100%) descent – 53 degrees (110%)
Gross Vehicle Weight: 23,369 lbs to 30,864 lbs
10,600 kg to 14,000 kg
Base engine: MB OM366LA 6.0 liter diesel (with Blue Tec – Euro 5 emission standard)
Power output: 240 bhp at 2400 rpm – more powerful engines are available on request.
Torque: 627 pound foot (850Nm)
Variable speed power takeoff and up to two independent hydraulic systems.
Note: All data taken from official specification sheets published by the Daimler-Benz AG,
The truck chassis of the Unimog 2450 L 38 is very popular throughout the world – from Europe to Africa and the Middle East, to Asia (Japan and Thailand), to Australia, and to South and Central America. It makes for a perfect platform to build a difficult to challenge Brush Engine, Fire Rescue, Mining and Expedition truck. It is extremely agile and can negotiate narrow mountain roads, as well as streets of ancient villages, steep forest trails and the countryside with ease.
The Cote d’Azur region in southern France faces very similar wildland urban interface challenges as southern California. The terrain goes from the beaches on the Mediterranean to foothills and steep alpine regions rather quickly. The vegetation is predominantly brush and conifer forests. Like California’s Santa Ana winds, this region too is affected by powerful winds that sweep across the ocean from the Sahara desert – the hot Mistral winds. Marseille, St. Tropez, Nice and Monaco are the four largest urban centers and have extensive wildland urban interfaces. The Cote d'Azur is also home to some of the most expensive real estate in Europe. Marseille, the second largest city in France with 840.000 residents has a very experienced tactical wildfire division, the “Marins Pompiers”. This special division of Marseille’s Fire Department employs 52 Unimog Brush Engines based on versions of the U-5000 chassis. Most are built on the standard 4x4 version, but some are constructed on the special 6x6 chassis. These units carry on board a crew of five, powerful pumps, 1850 gallons of water, 320 gallons of foam mix and a full complement of firefighting gear.
The powerful Unimog 2450 Brush Engine would be an excellent addition to strengthen the fire fighting capabilities in the San Bernadino Mountains of southern California - or elsewhere in challenging wildland interface environments. It can easily enter the complex access road system in Arrowhead Woods, where a Type 3 has no chance. The steep slopes and narrow roads in Crestline are not an issue. All the old communities with less than favorable narrow roads and water delivery infrastructure like Twin Peaks, Arrowhead Villas, Cedar Glen, Crest Park, Arrowbear, Green Valley Lake, Fawnskin, Big Bear Lake and City, Angelus Oaks and other enclaves not mentioned here would all benefit from being protected by such a brush engine in addition to the standard Type 3 Brush Engine.
Please see the Picture Gallery for additional examples and detailed information.