Although I'm a big advocate of scrapers this isn't something I'd personally do by scraping alone unless I had a paint scraper (AKA hook scraper). A thick layer of paint made up of multiple layers built up over time is particularly resistant to a conventional scraping action with less-robust scrapers, as you can get a parting of the ways between subsequent coats. What this means in practice is that you might have to go over a given area multiple times before you're down to bare wood (DAMHIK).
If you use a dedicated paint scraper such as the ones above instead of wimpier options (e.g. card scraper, shaving hook) you should have better results because they have a very aggressive scraping action. But still it would likely require substantial muscle effort, although the type of paint and just how thick it is are obviously factors here.
Heat/flame + scrapers
Although there are safer chemical strippers (note: almost invariably much slower than their nastier cousins) the other traditional option for removing a heavy coating of paint was to use a blowtorch, which you can still use, or alternatively a heat gun which is a little safer.
Oddly this seems to work best on thick paint. Some of that might be a user reaction to how amazingly it softens and releases that much paint, but thicker paint does tend to sort of 'sheet off' where a thin coat tends to cling to the surface more tenaciously.
A scrub plane/roughing plane (or a jack with a good camber on the iron) can be a great way to get off a very thick coating of paint, just as it's a great way to remove a shaggy or heavily weathered surface from wood. Working diagonally over the wood this requires surprisingly little effort.
It's perhaps too aggressive for the handtool-only guy who would then have to flatten off entirely by hand, but with a planer to smooth the wood afterwards it's worth considering this approach for its speed and effectiveness.
I wouldn't do this level of paint removal by sanding pretty much ever, there are just too many downsides. Cost of the belts is an obvious one, as is the mess (even with dust extraction the amount of dust released can be pretty bad). The potential to 'dub over' the wood or is also very high. Worst though is the potential toxicity of the paint dust not captured by any dust extraction and it's not just lead paint that we have to wary of — all paints and other finishes should be considered harmful when converted to a fine dust.