Also, why does "the speed heater / silent paint remover" not release toxic lead fumes but a heat gun does?

"Also, why does "the speed heater / silent paint remover" not release toxic lead fumes but a heat gun does?"

If used correctly neither will heat up the paint high enough to release lead vapor.

Heat guns are more frowned upon since the super heated air can pass through cracks into unseen areas and ignite things.

If you are stripping a door on sawhorses a heat gun works very well.

If you are striping trim on sawhorses it works fine also.

if you are striping trim in place the heat gun can put sir into stud cavities by getting behind the trim near a door jamb.

I think a door would be a good 1st project - as long as it not ornate. Outdoors is best, on mentioned sawhorses.. (If you find yourself in over your head w/it, lol, send it to the shop doing the trim?).

A heat gun is a pretty cheap investment - IR, not cheap.

Old, original doors - are your biggest investment by far, (IMO). I'd suggest to someone who hasn't stripped paint before, with chemicals or heat gun, to go to a thrift store & get a small table or something with many layers of paint on it, & use it for practice. That way, you can familiarize yourself with the way they work - especially the heat gun. It's easy to underestimate the "heat" & scorch the wood, until you get the hang of it. Better to make beginner mistakes on something you don't care about, right?
That's what I did, & I was glad - I did scorch the little table a bit but it sanded out. Unfortunately, it didn't have a heavy varnish layer for me to learn from... :-(
Good luck with it - sounds like a fun project, to me!

I agree with Brickeye about the risks of a heat gun properly used, which is on exposed, disconnected elements.

But there are also other methods you can use on doors.

1) Heat plate

2) Steam

3) Solvents like Soygel or its citrus equivalent

All of these will work, and each has its own advantage and disadvantage in terms of speed, convenience, lead hazard, potential damage to the doors, etc. You might try each as different types of paint are more or less resistant to one or the other.

All will have produce the same lead-hazard risk from the removed paint materials since chips, flakes, scraps, dust particles, etc. are what creates that risk.

You will need some place where you can work that you can contain and segregate the stripping detritus. If you're planning a long seige, I would suggest having some specially-designated coveralls and shoes etc. that you only use for this task, and don't wear away from the project. Periodically, or after it's all done, you can clean these separately from your other laundry. It's a great timesaver to have "stripping clothes" ready whenever you are.

The silent paint remover works by loosening the paint at a lower temp than some heat guns, hence not vaporizing the lead so you can't inhale it. But some heat guns are also lower temp, so safe from creating vapor when used correctly. All methods and any subsequent steps that create dust, including any sanding or scraping can create inhale-able lead dust.

HTH
L

Standing things up vertically has a lot to recommend it especially where heat methods are involved;
The paint waste is going to fall by gravity, for one. Which means it's not going to require your attention and effort to keep the debris out of the way.
Secondly, you will not be leaning over the work, so the "smoke" and "vapors" will not be in a direct path to your lungs, bloodstream and brain!
3) I think it's less back strain to have the work in front, not try to each across & over a door.
I do however lay them out flat for the sanding step.
Casey

Great idea, standing doors up! It would also make containment easier - smaller "debris-field", smaller tarps under.

(Just being outside, doesn't mean you should "let the chips fall where they may" - or however that saying goes). Especially if it's a LOT of paint layers from an object with a lot of surface area, like a door. :-)