Hi Tim,
We do tank entry on a purely voluntary basis, no extra money although at times overtime does pop up that's only available for people who are tank trained.
We use Sabre tank entry equipment which seems to be very reliable and user friendly other than the unwieldy hoses.
Main risks are injury to limbs clambering over the wing structure or obviously getting stuck. Risk of danger from fumes or explosion are totally minimised if not eliminated by use of a trained team and rigid procedures.
We also use rescue mats in some aircraft types which can be slightly inflated for comfort to lie on while working or fully inflated to aid recovery of an unconcious person on aircraft types with particularly deep wing ribs.
We also use oxygen alarms which double up as explosive fume detectors, these can be a little flaky though.
I'd say it's very rare for us to use the Sabre kit on the face in well vented tanks unless sealing or cleaning with solvents but we do always have the kit in with us clipped on in case the alarm goes off.
You need to choose your staff carefully, someone with problems in enclosed places is going to be a nightmare. There really is nothing worse than someone panicking or getting stuck head first a few ribs away from the entry panel. Some love it, some hate it. I'd say extra pay is an incentive but the overtime carrot seems to work well where I am!
I highly recomment the use of disposable entry suits too and counting tools in and out.
Good luck
