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| The Seattle Fire Department changed its fleet to rear-mount aerials to give the department some flexibility and to reduce the number of backing accidents that caused expensive damage to the ladder and monitor. Raul Angulo is captain of the department’s Ladder Company No. 6, a 2001 E-ONE. (Fire Apparatus Photo) |
One of the advantages of being in a large metropolitan fire department is the opportunity to ride on different apparatus. Though you may be assigned to an engine company, you can be assigned to a ladder company for the shift due to trades, overtime and other staffing issues.
I recently transferred to Seattle’s Ladder Company 6, a 2001 E-ONE 100-foot rear-mount aerial, located on Queen Anne Hill. Though I have worked on aerials throughout my career, this is my first assignment as a truck captain. In the Seattle Fire Department, there are 11 ladder companies. Four are tillered aerials, the rest are rear-mount aerials. SFD used to have mid-mount, straight chassis ladder trucks, but we moved away from them for a variety of reasons.
Having worked on both mid-mount and rear-mount aerial ladder trucks, and being a student of fireground strategy and tactics, I am of the opinion that rear-mount aerials are the way to go.
The most critical aspect in preparing an aerial for safe operation is stabilizing the apparatus. When an aerial is raised and extended, there are many twisting and torsional forces applied to the ladder. The weight distribution ratios have been compared to a teeter-totter/fulcrum system to help firefighters understand the gravitational forces at play.
The stability of an aerial is increased by operating the ladder in-line with the longitudinal axis of the chassis. The most desirable position for operating the aerial is directly over the front cab of the apparatus or directly off the rear of the truck. This in-line position uses the entire weight of the truck to stabilize the ladder and also distributes the weight of an extended aerial evenly throughout the rig.
Increasing the angle of the aerial away from this longitudinal axis of the apparatus decreases the amount of load that can be safely carried by the ladder. An angle perpendicular to the apparatus is the weakest position available.
With the modern aerials on the market, there’s really not a whole lot of differences between to two types. The ladders are so strong and beefy, they can be deployed from any angle without worrying about the stability of the ladder. Nevertheless aerial ladders are not cranes. Remember that. Since there are many older models still in service throughout the country, established stability principles still apply and should be adhered to.
Rear-mounted aerials provide more flexibility on the fireground. To begin with, they allow for quick deployment of the aerial. The truck can nose in to the objective, and the aerial can be raised and extended right over the cab without any rotation of the turntable. Some mid-mount aerials have trouble extending over the cab at low angles because of clearance.
Aerials that are extended from the rear of a mid-mount ladder cannot extend below the bed brackets of the apparatus. Rear-mounted aerials can drop 3 to 5 degrees below the back of the apparatus. This is helpful for recon, rescue, and reaching over the edge of a bridge, a freeway overpass, over water, and off a hillside.
Achieving Full Reach
Spotting or positioning apparatus on the fireground is an evolution and an area where all fire departments could stand improvement. Engine companies are often first on scene. If they spot in the wrong position and begin laying attack and supply lines, they inevitably block access to the building by aerial apparatus.
The turntable should be directly in line with the intended target. With mid-mount aerials, engines blocking the front of the building severely limit the reach of this type of aerial. The length of the apparatus prevents the rig from positioning the turntable for optimum deployment.
A rear-mounted aerial can back in to the front of the building, between engine apparatus, and position the turntable to achieve the full reach of a 100-foot aerial ladder. It is only limited by the width of the apparatus, not the length. If a space can accommodate the width of the truck, it should be able to back in and get the turntable into place for deployment.
Backing a rear-mounted aerial into the building gets the turntable as close as possible to the objective. This maximizes the reach and height of the ladder. Backing in, perpendicular to a building, allows a rear-mount to clear overhead wires and overhead obstructions with the turntable, allowing the ladder to be deployed where a mid-mount is prevented by its length.
If the rear-mount is backed into the corner of a building, (i.e. A-B corner), the entire apparatus is out of the collapse zone. A mid-mount aerial in the same position would still have part of the truck extending into the collapse zones on the A and B sides. If the apparatus has to make a quick exit from the area, the rear-mount is already in a position to drive away from the building once the aerial is bedded. A mid-mount would still be within the collapse zone while it was driving away.
Rear-mounted aerials can back into dead-end alleys and driveways, thus getting the turntable closer to the objective.
Assuming the aerials are not pre-plumbed, a rear-mount aerial allows for easier stretching of the ladder pipe supply hose line. With the mid-mount, the cab and the ladder bed often make it cumbersome to stretch the hose for the ladder pipe evolution.
In the same fashion, a rear-mounted aerial allows for easy removal of a Stokes rescue basket, or litter, being slid down the ladder. The litter can be passed down to firefighters on the ground.
In the same evolution with the mid-mount, the cab and the ladder bed can get in the way depending on where the ladder is extended. This will require firefighters to lift the Stokes litter over the ladder rails to clear the turntable. In rain or snow, slippery conditions can make this tricky for firefighters and the patient in the litter.
There are some limitations with mid-mount aerials, and one of them is side deployment at 90 degrees with the ladder fully extended, especially at low angles. It is less stable and puts the most stress on the ladder.
Aerial Stability
Believe it or not, raising and extending the ladders of toy aerial models, like the Code 3 collectibles, can accurately illustrate stable and unstable ladder angles. Putting fingertip pressure at the tip of the ladder extended along the axis of the model reveals strong resistance. Swing the aerial 90 degrees to the right or left and apply fingertip pressure to the tip of the ladder and the entire model can easily tip over. Jacks and outriggers would prevent this on a full-sized apparatus, but the physics are the same.
One of the advantages claimed for the use of mid-mount aerials is that the turntable is right behind the crew cab. This allows for firefighters to quickly access and climb the aerial ladder for rescue. While that may be true, more often the entire crew usually assists in setting jacks and outriggers.
A rear-mount forces the firefighters to walk to the back of the apparatus before climbing the ladder. This allows for a few more seconds to assess and size up the situation they are about to enter. Firefighters can check how many stories are in the building, take note of wind direction by watching the smoke and determine which way the fire is traveling.
Chassis designs vary, but most rear-mount aerials tend to have a shorter wheelbase, allowing them to turn on a dime with excellent turning radius. There is better awareness of the aerial tip when it extends over the cab. The tip is in full view of the apparatus driver and there is less chance of striking a stationary object or an overhang.
Mid-mounts aerials tend to swing wide on turns. The tip of the aerial is hanging off the back of the apparatus and is not visible in the rear view mirrors. Most accidents involving fire apparatus are backing accidents.
Pre-plumbed, mid-mount aerials not only have the ladder extending beyond the apparatus, they most often have expensive master stream nozzles exposed as well. A mid-mount backing accident can damage the aerial ladder, the nozzle and can crack the plumbing. Those can be expensive repairs for any fire department budget – and were the primary factor for the Seattle Fire Department switching to rear-mount aerials.
Again, the new monster truck aerials are stronger than ever, and mid-mount and rear-mount aerials are safe to operate at any angle. Older aerials could barely lift their own weight while fully extended at vertical zero degrees. New ladders can be fully extended at a vertical zero degree and easily lift two firefighters hanging from the tip. Physics and gravity still apply, and it’s important to remember that no aerial is failsafe.
So here’s the bottom line for me: No matter how fancy or strong your aerial apparatus is, parked cars, narrow streets, and poorly spotted fire engines can deny or limit access to mid-mounted aerials.
A rear-mount aerial can back and squeeze into a tight space as long as it can accommodate its width. This provides options to firefighters, and that’s important on a dynamic fireground.
Editor’s Note: Raul A. Angulo is a 27-year veteran of the Seattle Fire Department and captain of Ladder Company 6. He is on the advisory board for the Fire Department Instructors Conference and on the board of directors for the Fellowship of Christian Firefighters. He writes for numerous fire service publications and is an instructor on fire service leadership, company officer development and fireground strategy and tactics. He teaches throughout the U.S., Canada and Mexico.
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