My personal experience has been that old conductors unable to dump heat suffer quite a loss of their insulation value over time.
I'd seriously recommend that utilities de-rate the ampacity of older cable before they let the smoke out.
Is there any possibility of the hot lines being de-energized long enough so that they can be hi-potted?
If not... I'd be paranoid.
Even if the hot cables are blanketed I'd want my down-hole time absolutely as low as possible. I'd be very reluctant to let the troops forgo protective gear.
The tugging schemes I've in mind do NOT require a lot of down-hole time. So I'd be very reluctant to play it slack.
My biggest worry is the nasty atmospheres found below grade. Please, ventilate generously.
