Yeah, it's -70 (F) with wind chill. Pretty bad, but not the worst ever. The worst I've ever had to actually go outside and work in was -55 (F) ambient, -100 (F) + (or minus?) with the wind chill. The worst part is when you are really, really fuck*ng cold and your extremities hurt and you know you have no option but to stay out for a few more minutes before you can go in, or you realize that you can stay out a few more, or have to go back out in a bit for a longer amount of time.
We have these runs of pipe that we have to hammer up for semi-permanent installations to move fluids or gas. Back when I spent lots of time outside doing manual labor stuff, we were knocking one of them up (the connections are threaded, but tightened by hitting them with sledges) and a big chunk of metal split off and flew up and struck me right in the mouth, and my lower lip sort of exploded. That sucked, but there was nothing for it but to finish up. I also once had someone set down a chunk of iron weighing about 250 lbs (a valve assembly) on the tip of one of my fingers, splitting it open. I knew it was all fucked, but I just left the glove on and finished up, because what are you going to do? There ain't no fixing it, and I knew if I took my glove off I was done for the day.
Fortunately any more they let you stop and take breaks whenever you need, for pretty much as long as it takes. It's a much more forgiving place to work nowadays (hey, thanks for being reasonable once I move inside you bastards).