He's on wgbh 89.7FM and has a daily weather podcast in the mornings, Weather Wisdom, that's a great short listen

Came here to say this, I listen to it every morning and he's really insightful and informative

Yeah it's fucked a, b, and c is my professional opinion but I'm not on site or actually giving a professional opinion. I'm so glad you're consulting w folks local to make sure it's all safe... Most folks dgaf. I've been at it professionally for almost 20 and only screaming about lead about ten years ago when I exposed a kid and it got pretty real

A bit of insight on what I see in this photo - there's a calcimine coating as well as lead paint (you can test it for lead for kicks, calcimine is less harmful - used to be used as a washable coating for ceilings etc when we burned coal or wood inside) - the calcimine is the unstable coating (if you have any other old ceilings in your house that aren't covered they may develop a pattern like this but on a way lesser scale as they're coated more recently). The instability of those ceiling coatings means that it will all come off.. In very small and particulate pieces.

I would very honestly recommend that you don't open that any further and patch the hole, I'm sorry...that (definitely) lead substrate is so unstable that if I ran into that at my own (1912) house - I'd set down my tools and set a 20-30k budget to deal with it (which would be pulling the whole ceiling+ but still wouldn't be lead abatement). And for that kind of money I'd deal with the stupid ass soffit and spend it elsewhere. It's totally possible and legally you can tear that shit up as a homeowner but I wouldn't touch it were it mine... Just my $0.02... I'm sorry
If you are hellbent or if you have any other lead questions happy to advise you how to do as safely as possble but don't.

Re reading your original post I would demo as little as possible, do you have to pull the whole ceiling?

Was the soffit added later? Maybe when HVAC was put in or last kitchen reno? Lil weird to see a proper lathe & plaster ceiling with a soffit

Oh my I'm happy to help...fwiw I rarely test and we assume that it's present in homes of a certain vintage because it's there. Lead is also likely there in any stained finishes mainly pre 1960s so be aware of that too if ever refinishing floors or stained trim, the varnish used to have lead in it... Anyways, my expertise and certs are related to lead and not asbestos, but afaik the same dust and air control mitigation measures with regard to people and air are generally the same. Full face respirator (shave and leak test!), hooded tykek suit, booties, etc. Since you're working at home I'd be as nude as possible underneath, remove PPE outside and controlled as you can.

Or you can just assume that the lead is present. RRP (Renovate Right Program, the EPA regulations for lead renovation) says that the presence of lead doesn't matter if you're the homeowner which is super stupid but I'm glad you're taking precautions.
You're pretty close with what you're doing but:

• need to put plastic on floor and covering any fixtures/furnishings, sealed with tape to the wall. Must be completely sealed. You'll still have to hepa vac everything after you get this up.
• Disposal is just wrapping up that floor covering and all other debris in 2 plastic bags, each wrapped up and taped or tied off, then you can put in regular waste
• Any vents or other openings to other parts of the house must also be sealed. (Doorways)
• I'd strongly recommend renting a negative air machine rather than your box fan plan, they're super cheap. Not required by the regs for homeowners but is for RRP work so please spend the 40 bucks or whatever it is if you'll only need it for a day, or whatever however long you need it... Get a negative air machine please
  If you have any other questions please give a shout, I'm happy people are trying to be safe about this.

Source: licensed lead renovator specializing in antique new england homes

You're not a smart fella are ya?
You don't have to bother to answer, dunce ass fuckwad... It'll do you no good.
Have a shitty day, pal.

I have some pis, these look really cool, especially the M12 mount