Subject: Winch Operations at Rescue Scenes Topic: Things You Ought to Know About Using a Winch at Rescue Scenes Objective: Understand the safety concerns and critical operational features of a winch when used at a rescue scene Task: Using the...
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Subject: Winch Operations at Rescue Scenes
Topic: Things You Ought to Know About Using a Winch at Rescue Scenes
Objective: Understand the safety concerns and critical operational features of a winch when used at a rescue scene
Task: Using the winch and accessory equipment operated by your agency, develop operational winch guidelines to insure safe and efficient winch operations at incident scenes.
This article could actually be titled “Things You Probably Don’t Know About Winches.” Each of the items listed is an important safety or operational point for any agency to consider when performing equipment maintenance, conducting hands-on training, or operating a winch system at a rescue incident. Although not a complete listing, these items are some of the more critical elements of winch systems. Further details are available from sources such as winch system manufacturers and heavy rescue-oriented training programs.
Before we get started, some winch terminology must be understood:
Wire rope – Often called “cable” by firefighters and rescue personnel, it consists of many thin steel wires grouped into bundles to form strands. Multiple strands of wire are then twisted together around a core to form a complete wire-rope assembly.
Wrap – A single coil of wire rope wound on the drum of a winch.
Layer – All wraps of wire rope around a winch drum that are on the same level.
Item: The capacity of a winch decreases as more layers of cable wrap around the drum.
Every winch has a rating; a maximum load that it can pull with its line. For example, yours may be rated at 8,000 pounds or 20,000 pounds. But do you know what that really means? All winch ratings are actually “first- layer” ratings. This means that the maximum pulling capacity of a winch is only at the first layer; when all cable is off the drum except the very first layer of cable. The capacity of a winch decreases as more layers of cable wrap around the drum. For example, a typical fire department 8,000-pound winch using three-eighths-inch wire rope has actually five ratings, depending upon which layer of cable is doing the pulling:
- 1st layer – 8,000 pounds
- 2nd layer – 6,700 pounds
- 3rd layer – 5,700 pounds
- 4th layer – 5,000 pounds
- 5th layer – 4,500 pounds
As a rule of thumb, for each layer of wire rope on the drum, deduct 10% to 12% off the rated line pull (http://www.innovation-engineering.co.uk/theory.htm). Generally, when all the cable is on a winch, the pulling capacity is only one half (50%) of its full rating. The change is due to the cable that is pulling the load actually getting farther away from the axis or center drum of the winch – a good reason to pull off lengths of wire rope and rig up a pulley system with your winch. The mechanical advantage can double your pulling power and get the pull closer to the first-layer winch rating. Also notice as cable builds up layers on a winch drum, the speed that the line moves increases to nearly double the first-layer speed.
Item: You have to always leave some cable on the drum.
Always leave a minimum of five wraps of wire rope on the drum at the bottom layer to achieve a rated load. This is a safety feature that keeps the line from pulling completely off the winch drum. Five layers on the drum is the minimum!
Item: There are good reasons to place a heavy canvas or duck tarp over winch lines.
Part 1 of this series described an actual incident where the failure of a tow truck’s cable under load instantly caused 35 feet of broken cable to release uncontrollably. Winch operators should always make sure that everyone keeps well back and away from any winching activity. It is good practice to use a heavy blanket or heavy weight tarp over the wire rope during a pulling set up. In that way, if a rope failure should occur, the weight of the tarp will act as a damper and help minimize the whipping of the broken cable. For operator safety, raising the vehicle’s hood can also give some protection should the rope break. Also, during winching, the tarp acts as a visual warning to rescue personnel, preventing them from walking into or tripping over the wire rope.