Mike Wilbur

Mike Wilbur: Aerial Apparatus Operational Footprint and Scrub Area

When buying aerial apparatus, fire departments strive to purchase a vehicle that will at least serve 90 percent of the first- due response area, knowing that because of the size of aerial equipment today, it is not a one-size-fits-all proposition. Therefore, it becomes vitally important to determine the aerial apparatus operational footprint.

What is the operational footprint? It is the area on the fireground the vehicle will occupy.  To calculate this space, the aerial apparatus must be set up with all jacks and outriggers fully deployed. Then the aerial device must be set up at a 90-degree angle to the chassis with the device at zero degrees of elevation. This is the most physical room the vehicle can occupy without extending the aerial device. If you drop the aerial device below zero degrees or you raise the aerial device above zero degrees of elevation, it will shrink the aerial apparatus footprint. To obtain the maximum apparatus operational footprint, measure from the side of the apparatus body out to the farthest point out to the aerial device–in many cases, probably the ladder pipe at the tip of the aerial or on the front of the platform in the case of an aerial tower or tower ladder (photo 1).  Then you must measure the width of the chassis best to do this at the rear by measuring the rear bumper (Photo 2). Now you measure the longest out board jack or outrigger (Photo 3).

(1-3) Photos courtesy of author.

 

 

“The outboard side of the apparatus” is an interchangeable term and is used to describe the nonfire or nonworking side of the aerial apparatus. Now, add each of the values derived from the measurements taken. The sum equals the maximum operational footprint.

If you have a four-section rear-mounted aerial ladder, you should have measurements somewhere between 40 feet and 42 feet. For a three-section, rear-mounted aerial tower, the measurement should be between 48 feet and 52 feet. The measurement for a five-section mid-mounted aerial tower should be between 36 feet and 40 feet. If you short jack the apparatus (not fully deploy the outboard or nonfire side jacks or outriggers) (photo 4), you will arrive at the minimum operational foot print.

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What practical application would this information have on the fireground? If you had a two-story row of stores on Main Street, U.S.A., on fire and you wanted to use your aerial device as an offensive weapon in this fight, you could measure the distance between the stores on opposite sides of the street, including the street itself, and compare them with the apparatus measurements you obtained, you would soon learn whether your aerial device will fit on the Main Street in your town.

The scrub area is defined as that area of the fire building that can be touched with the platform basket from a tower ladder or the tip of an aerial ladder. With the exception of large cities such as New York, Boston, Los Angles, Phoenix, Houston, so on, most urban / suburban fire departments use their aerial devices more in a horizontal plane than in a vertical plane.

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Estimating Horizontal Reach

To estimate the horizontal reach of your aerial device, set the aerial device chassis up with the ladder or boom at a 90˚angle to the chassis at zero degrees of elevation. Measure from the bottom of the ladder’s bottom beam or from the bottom of the boom to the ground. For a more accurate estimate, conduct this part of the drill on a level paved apparatus apron or in a parking lot (photo 5).  Subtract this measurement from the rated vertical reach (this is basically subtracting the chassis out of the equation), and you have the horizontal reach off one side of the chassis. For example, if you have a five-section, mid-mounted aerial tower, the tower’s aerial device is rated at 95 feet vertically. The measurement from the ladder’s bottom beam to the ground should be about seven feet. That should give you about 88 feet of vertical scrub area off one side of the chassis, but you can position to use both sides, which would be 176 feet–if the turntable is right up against the side of the building. However, we do not want to be in a potential collapse zone, so we would position the apparatus one boom length away from the building line, which would result in a horizontal scrub area of about 160 feet.

One question often asked is whether a mid-mounted aerial tower or a rear-mounted aerial tower has a better scrub area. Rear-mounted aerial towers generally have three ladder sections, each one about 31 feet in length. Put them together with a platform on the end of it, and you will have a measurement of somewhere between 36 feet and 38 feet off the side of the apparatus at zero degrees of elevation.  A mid-mounted aerial tower generally has five sections, each section measuring 16 feet to 18 feet; put them together with a platform on the end, and you will have a measurement of 24 feet to 26 feet off the side of theapparatus at zero degrees. This is a full 12 feet to 14 feet less than a rear-mounted aerial tower.

What application does this new-found knowledge have for the fireground?  The closer you can get the aerial apparatus at zero degrees of elevation to the fire building for a lower-floor fire, more the side-to-side scrub area increases. Conversely, the farther away from the fire building at zero degrees the apparatus is positioned, the less the side-to-side scrub area.

BIO

MIKE WILBUR was a volunteer firefighter for more than 40 years and a career firefighter with the Fire Department of New York for 32 years; he retired in 2013 as a lieutenant. He served on Ladder Companies 56 and 27, served on the FDNY apparatus purchasing committee, and has state certification from the FDNY chauffeur school. He was a member of the IFSTA validation committees for the Apparatus Operator and Aerial Operator Manuals and on the United States Fire Administration’s Safe Operation of Fire Tankers and Emergency Vehicle Safety Initiative.

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