Originally posted by Flingblade:
Is the reason they expire because of the plastic buckles? I don't remember any expiration on mine and it has no plastic on it.
It's because of general material degradation. Dust, dirt, sand etc... gets into the fibers of the harness & into the stitching & begins to abrade them, possibly harming their integrity & weakening the straps.
UV light can & will begin to break down the strength of any nylon, polypropylene or polyethylene fibers, including the buckles.
I'm 99.999% sure that a harnes that is 20 years old would be safe to use, if it hasn't taken a fall, but the manufacturers need to account for a very large safety margin. Imagine the furore if, say, an HSS harness failed. It would probably bankrupt the business overnight.
Bear in mind these harnesses are designed to save your life. Not minimise risk, not make you
feel safe, but actually stop a 300lb person from falling & dying. That's a hell of a lot to ask from a few nylon straps & buckles.
Yes the good harnesses are expensive, but do you really, honestly want to trust your life t the lowest bidder? I sure as shoot don't.