“because instrumentation lines froze”
That might be true but if they’re electrical lines, how do they freeze?
Could there be instrumentation lines that contain a freezable liquid? Do they mean an overhead line that collected ice and broke?
Some instrumentation runs on air and those lines are prone to issues if not kept dry.
The frozen lines are probably referring to boiler operations. All boilers use a variety of different pipes that connect pressure and temperature transducers, different supply lines for water and steam. Usually the water and steam are hot enough to keep the lines from freezing. But if it gets cold enough and the lines lack adequate protection they will freeze.
“That might be true but if they’re electrical lines, how do they freeze? Could there be instrumentation lines that contain a freezable liquid? Do they mean an overhead line that collected ice and broke?”
Sure, they can carry air (or gas) or liquids, to a remote gauge. Certainly that’s how it was done in the old days, and did have the advantage of not requiring power to operate (as is required if you do the measurement locally).