With a 3rd degree burn is it standard practice to drain a blister and cut off the skin from the blister?

Be careful: It is ok to clean the blister with soap and water or alcohol, and puncture it with a needle (it won't hurt). But, you want to leave the blister roof itself intact. Nature's bandage (your skin) is the best. Having said that, a 3rd degree burn is not to be taken lightly, and at any sign of infection, see your dermatologist.

No it not: Standard practice to drain any blister and cut the skin! ever from any cause! seek other help infection could occur.

Not 3rd degree: Blister means is 2nd degree not 3rd. Removal is a judgement call. Most would try to leave blister intact as long as possible unless interferes with function.