Ditto what has already been said about open flames on hull paint and fiberglass. The folks who have posted already have owned keel and other boats with training hulls longer then I have had a keel boat (SD has a trimaran and has an encyclopedic knowledge of all things related to boats - no BS).
Without knowing how big the boat is (is it a Tartan 37' or a Tiburon or what) and where it is located (Mexico? - I checked some of your other posts) and since you say you have some 'blister' issues on the hull I will tell you what little I think I do know.
The best (and one of the messiest and fastest) ways of removing hull paint, gel coat and fairing out any blisters will be with a tool called an 'angle grinder' or just a grinder. There are versions in 4 1/2" and 5" on up. Here is a link for a Makita 4-1/2" angle grinder: Amazon.com: Makita 9557PB 4-1/2-inch Angle Grinder w/Paddle Switch, (AC/DC): Your Store
which is a better model then the el-cheapo Black&Decker model I have.
You can buy semi-flexible sanding disks that you can attach to the grinder that come in varying grit sizes (#30, #60 etc) that I can't seem to find on any of the 'friendly' box store websites - grrh$#!+). I get them in a lumber store or hardware store for a buck or two a piece. Do not use a solid disk for this as it will do more harm then good. The flexible sanding disks (what I am calling them but no one else seems to) are good because they take off a significant amount of material quickly and are pretty easy to control if you keep them moving (unlike a belt sander which will quickly make a mess and make your hull un-fair (not smooth). The final sanding would need to be done with a normal flat Random Orbital sander to take out any of the 'proud' spots left over in the 'massive removal' stage. You were planning on putting a new barrier coat on anyway weren't you?
The problem with this kind of procedure is that it will make a hell of a lot of dust which many yards will not allow and the person doing the work needs to have a respirator, full suit and goggles etc (yes, even Mexicans should wear protective clothing for this kind of work if your work is being done in Mexico, which should cost a lot less).
Most will tell you just to use a heavy grit paper (#40 or #60) with a normal Random Orbital sander attached to a vacuum because you will not be able to mess up the shape of the hull too fast with a tool like that and I would agree. There is a certain amount of finesse one can gain though by working with these 'sanding disks' (that I can't find a ******* link for) with the angle grinder and the amount of pressure used that would take off the material much faster (and messy-er because the angle grinder has no vacuum attachment) but pretty evenly none the less.
Since I think that you have a 37' sailboat I am going to guess that you will probably not be doing the work yourself. Using the right tool or contractor for the job can make a messy, unforgiving job go faster.