Sam,

you may just be surprised how well a safety chain will hold together, we used to have a pair of Sidechains on freight with the old centre Buffer and Hook, not on Passenger with the knuckle couplers. These were removed around the early 90's.

I was firing one night, while being power braked coming into the yard and still moving around 5mph I got down on the rear footsteps to uncouple, my Enginedriver turned on the rear headlight and to my horror saw the loco was attached to the train with only one sidechain and that was as stretched as I had ever seen one be stretched. I stepped off smartly. He had around 1100 tons on that chain and had pulled it like that for some 12 miles uphill and down dale since our last lift at a siding.

Here's what they look like after a mishap.