The first time I went up a mast it was on a rope/wire halyard. Just as I reached the top of the mast the splice broke.
Fortunetly I had rigged a seperate halyard to a seperate harness and only suffered from having my life flash before my eyes as I dropped the four inches of slack in the safety
EVERYTIME you go up a mast you should rig two lines in such a way that there is no one piece your life depends on. No shackle, no knot
, no line, no block, no winch
, no wire, no harness nor chair should be the only thing between you and the deck
. If you go up in a bosun chair, your safety
line should be tied to a seperate harness. If you go up in a "climbing harness" attach your safety line to a chest harness.
If you are short on deck
crew to tend a second safety line, you can use a webbing strap that you wrap around the mast. If for some reason you fall, this will pull this tight and hold you. You will be very grateful for not hitting the deck, but unless you are part monkey, you will have the very devil of the time figuring out how to get down.
The only reason I can write these words of warning is because I did these things.