By Harrison Brookeman, MD
It is rare to find a heavy rescue truck in the United States without a winch installed in the front bumper. Increasingly, even engines and ladder trucks are now equipped with bumper-mounted winches.
Additionally, some rescue apparatus have winches installed in both front and rear bumpers. As winching technology has become lighter and more portable, the latest trend is to have portable winches that can fit into receiver hitches and be moved around all sides of a vehicle as needed. This allows apparatus operators to worry less about scene positioning, allowing for more diverse applications. As departments place more of these devices in service, many rescuers express little understanding of the forces involved and applications of winches. Although courses for the towing and recovery industry exist, there are few winching educational opportunities targeted at rescue professionals.
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A winch system’s strength is only as formidable as its weakest link. Apparatus training manuals generally list the rating of the winch as the maximum pull achievable, often neglecting discussion of safety factors. Additionally, a manufacturer’s manual provides limits, but those are calculated in isolation and in ideal mounting conditions. Is that winch rating the working load limit or the mean breaking strength? Most rescuers will only consider the ratings from the drum to the load, operating with the assumption that the fire truck is bulky enough to handle whatever is thrown at it. However, more goes into calculating how much pull you can safely achieve. Factors such as load composition; any damage it may have sustained in the accident; mechanical advantage systems; winch cable left spooled on the drum; and, most importantly, apparatus construction all play into the overall rating.
1 Initial scenarios used two heavy rescues with bumper-mounted winches. Each was set up for a 2:1 mechanical advantage. (Photos by author.)
2 The load cell after the failure shows a maximum tension of 7,800 pounds noted by the red needle.
3 Driver-side mounting points of the front bumper assembly, which contained the 15,000-pound winch. The smaller holes had the bolt heads pull through. The larger holes are believed to be for 1-inch bolts that were never installed by the manufacturer.
Agencies should follow a winch inspection protocol after using the winch for training or on a call. They should pull the line all the way out, inspect it for damage, and rewind it based on manufacturer recommendations. If your department does conduct inspections, when was the last time you crawled under the truck to inspect how the winch is attached to the frame? When your apparatus was being built at the manufacturer, did you specify how the winch body should be attached to the frame? Did the vehicle engineers provide a working load limit? Did you crawl under and evaluate the bolts holding everything together? For many, the winch is operated as if it stands in isolation from what it is attached to. In rope rescue, each connection point is generally visible for inspection. However, with an apparatus-mounted winch, years of salt, road debris, or even misconstruction may have gone unnoticed.
TRAINING SCENARIO
During a heavy vehicle rescue class, two heavy rescue trucks had been used in tandem throughout the day to conduct a controlled roll of a partially loaded MC306 tanker that was overturned on a passenger vehicle. During the final scenario of the day, students questioned if a single heavy rescue truck using a 2:1 mechanical advantage configuration could perform the controlled roll given that the prior scenarios had been performed with ease and having calculated the tension required for the prior rolls from the load cells. Two senior operators and the lead instructor were present and believed that the 15,000-pound bumper-mounted winch could be used to its full capacity. The static anchor point for the 2:1 mechanical advantage was tied back to a tow connection on the bumper with a load cell placed in line to monitor the tension.
When everything was set, the lift began, and the tanker began rolling off the passenger vehicle with ease. However, as the load approached 7,800 pounds on the dynamometer (2:1 configuration = 15,600 pounds total load), there was a loud crash, and the front bumper became partially separated from the heavy rescue. Thankfully, no one was injured either from the bumper or the sudden drop of the tanker. The dynamometer captured the final maximum tension as pictured in photo 2.
Although the total tension of 15,600 pounds exceeded the winch’s maximum, the assumption was that there was at least a margin of safety factor in the construction of the bumper based on a manufacturer installing a 15,000-pound winch—more than 600 pounds. As the truck had been constructed almost two decades ago, that information was unfortunately unknown.
It is best practice to identify a separate anchor for the static point for a mechanical advantage but, in this case, as in many failures, we believed to be operating within the design specifications of the truck. As the bumper lay half off the frame, it became clear why the bumper catastrophically failed. The bumper construction and winch attachment was laid bare for all to see. The winch and anchor points were not attached directly to the main truck frame as believed. Instead, a smaller subframe had been constructed and attached to the longitudinal frame rails with standard 1⁄4-20 bolts and a weld along each side. Missing were the large 1-inch bolts that were supposed to attach the bumper and winch assembly to the truck frame.
This failure proved to be a learning opportunity. Afterward, all other vehicle-mounted winches were evaluated for proper hardware attaching them to the vehicle. Additionally, any apparatus with hitch-mounted winches had the hitches and frames evaluated.
Take our mistakes as an example. Many years and many winching scenarios had gone by without an incident. However, all it takes is the right alignment of conditions to cause catastrophic failure. Do you really know what the limits of your trucks are? I urge you to investigate for yourself.
HARRISON BROOKEMAN, MD, is an emergency physician and a captain with the Charlottesville-Albemarle Rescue Squad in Charlottesville, Virginia. He has been a member of both career and volunteer agencies since 2011 and spent most of his time focusing on technical rescue. He has taught numerous passenger and heavy vehicle rescue courses throughout Virginia.
