Using Aerials and Digger Derricks in Slick Conditions
As we enter the full grip of winter, setting up aerial devices and digger derricks in snowy and icy conditions brings additional concerns for equipment operators. Normal traction is greatly reduced, which could put a truck in an unstable position. Variable site locations – on gravel or grass, sloped or level – and the urgency to minimize electrical disruptions mean that utility crews often must make the most of imperfect conditions.
Upon arrival at the site, whenever possible, clear away snow and ice under outriggers and tires so that they are in contact with bare ground. Avoid setting outriggers on drains or manholes.
“All outriggers must be lowered to provide proper support, apply downward pressure on outriggers, and always use outrigger pads on a level surface,” advised Bruce Westergaard of Minnesota Municipal Utilities Association. He also suggested avoiding uneven seating, where the outrigger foot straddles mounds or spans dips, as well as using outrigger pads that are textured on the bottom.
Alternatively, traction aids under tires and outriggers – such as sand, gravel and mats – also are a good option.
“When working on frozen ground, a neoprene layer under the outrigger pad is an option for increasing friction,” said Kris Koberg, CEO of DICA (https://dicausa.com), a manufacturer of engineered outrigger pads. “Frozen ground is hard, and adding a neoprene sheet of sufficient thickness will allow pads to bend or deflect slightly, spreading the load over a larger area and creating better contact with the ground. The results are enhanced pad-to-ground contact, lower peak pressures and lower overall ground-bearing pressure. Generally, we have found that 3/4-inch-thick neoprene sheets create the friction you are looking for and significantly improve load distribution in these icy, hard ground situations.”
According to Jim Olson, senior product engineer for Terex Utilities (www.terex.com/utilities), “Keep in mind that snow and ice can build up on the truck during transportation and accumulate during operation. Brush off the snow dust from the contact surfaces, including the bottoms of outrigger feet as well as both top and bottom surfaces of the outrigger pads.”
Choose a Stable Location
Next, choose a location that provides the best stability for the work to be done.
“Position the truck as far onto the street or road as possible so that if your truck does move during operation, the tires and outriggers will not slide down a slope into a ditch, manhole or other hazard,” Olson said.
Caution is required even on pavement because “gravel on concrete can act like ball bearings under outriggers and outrigger pads,” Olson explained. Always refer to the manufacturer’s operator manual for information on proper setup and use of outriggers.
Operating within level tolerances is extremely important. If a slope is unavoidable, the bank of the slope may need to be cut away, or cribbing should be used to level the truck. When operating the unit on a slope, there is always the potential for the truck to move, even when working on dry pavement. This is due to gravity trying to pull the truck down the slope. When operating on a sloped surface that is covered in ice or snow, this effect is amplified, making it more likely that the truck will slide down the slope unless the proper precautions are taken during setup. Leveling the truck will not change the risk of sliding on the sloped surface because the outriggers and tires are still on the slope and can slide. The surface the outriggers sit on must be leveled or the traction improved to prevent sliding.
One option for leveling aerial devices and digger derricks are engineered cribbing blocks, which DICA manufactures. “ProStack Slot Lock and Pyramid Lock Cribbing Blocks interlock for a secure foundation, allowing operators to achieve the height needed to level the equipment,” Koberg said.
Chock the Wheels
Once in position, chock the wheels to prevent movement downhill, and evaluate the chock locations to make sure the truck won’t pivot around one chock. For example, if a truck is parked with the cab pointing slightly downhill, it should be chocked on the front and back of the tires. If it were chocked only on the front side of the back tires and the boom abruptly stopped, it could sway, causing the truck to pivot. This may even be evident on flat ground if there is not sufficient traction, or boom movements are rapid starts and stops.
Proper setup requires that outriggers do not slide on the outrigger pads during use, and that the outrigger pads do not slide on the ground. “This is a concern that comes up every winter,” Koberg said. “Over the years, we have worked with users to develop a variety of solutions to address different sliding issues, as there is no one-size-fits-all answer.”
In one situation, DICA worked with an electric cooperative to create a base of expanded metal in a frame. The metal frame was larger than the outrigger pad and positioned under it to help cut through snow and ice, giving the pad something to grip to.
Three off-the-shelf products that work in different scenarios are DICA’s Cleated Pads, with serrated cleat grips for improved traction; their standard Cavity Pad with raised sidewalls; and the company’s new Cavity Pad Plus, which features an inverted beveled footbrake that prevents the outrigger foot from escaping.
Reduce Sudden Boom Movements
Once proper setup is achieved and operation begins, it’s good practice to reduce sudden boom movements. “Operate the truck by feathering the controls so that all initial and final boom movements are performed at the lowest practical speed,” Olson said.
Removal of snow and ice, the use of traction aids, leveling of the truck, use of large or specialty outrigger pads, and engaging in slow, steady boom movements are some of the techniques and tools at the operator’s disposal to reduce the risk of the truck sliding down a slope in snowy or icy conditions.
If a unit begins to slide during operation, the operator should stop the boom functions. “Attempting any other operations when the machine is sliding out of control may compound the issue,” Olson said.
Recovery during operation is extremely difficult, which is why it is so important to prevent loss of traction before it happens. Finally, if roads are not sufficiently clear to enable proper setup, postpone the work until later.
About the Author: Craig Ries is a product safety engineer for Terex Utilities (www.terex.com/utilities).