4WD recoveries generally involve a lot of force, and if something breaks it can do a lot of damage. There's been more than a handful of people killed in Australia over the years when 4WD recoveries have gone wrong. One of the biggest risks in a 4WD recovery is that something metal breaks. If this happens, and its under tension (like a winch rope or snatch strap), its going to take off faster than you'll be able to see.
Shackles are a regular part of 4WD recoveries. The trouble though, is people attach them to places where they shouldn't!
What's a shackle?
In 4WD recoveries, you'll generally see two styles of shackles used. They are 3.25 tonne and 4.75 tonne. This is the working load limit, and defines what they are rated to. Almost always these are bow shackles, which bow out as a pose to normal Dee shackles.
I have a couple of 3.25 tonne shackles, but prefer to use the bigger ones.
If its not stamped, don't use it!
All shackles used for lifting, 4WD recoveries or substantial load should be stamped with a WLL. If it doesn't have one (like many trailer shackles), its not safe to use!
What makes a shackle so dangerous?
Rated shackles generally have a safety factor of 5 - 7 times their WLL. That means a 3.25 tonne shackle won't break unless you apply over 16 tonnes of force, and a 4.75 over 23 tonnes. In effect then, you probably won't break a shackle. Of course, this applies to quality made shackles with decent thread tolerances and quality control. Buy quality gear, once.
The point though, is that a shackle is very safe. However, it becomes insanely dangerous if what it is attached to breaks. These shackles are solid steel; they are heavy, and if you threw one at a person you'd badly hurt them. I've seen video's of pieces of steel (like tow balls) go through one side of a tyre!
Don't use shackles if you don't need to!
The aim of the game is always to reduce the number of potential missiles in a 4WD recovery. If you can get away without using a shackle, do so. The perfect example of this is people joining snatch straps together using shackles. It might seem safe, but if the strap breaks, you've got a missile that's going to kill someone. When you can safely join snatch straps with the correct method, you have no need to use a shackle.
Where is it safe to attach a shackle?
Shackles should only be attached to rated recovery points. A hitch receiver for example, is designed to take a 4.75 tonne shackle. Rated recovery points like those made by Roadsafe are also intended to take a shackle.
Holes on bull bars are not designed to take a shackle, especially the ARB bullbars which have two holes that catch a lot of people out. Tow balls are not safe to use a shackle on, and neither are trailer chain attachment points, tow ball holes and factory tie down loops.
Recently, soft shackles have become more popular. They are basically dyneema winch rope made into a shackle. Obviously they won't be as durable, but they weigh next to nothing, are equally strong and reduce the risk dramatically. This is a great alternative.