Shale is kind of closed cell porosity until you break it up to release the trapped material. That's how they are getting oil out of it in the Bakken and a few other places. Drill horizontally into the seam, then apply ungodly amounts of hydraulic pressure to frack it and inject sand to act as proppant and hold open the cracks once the fluid pressure is relieved.

Probably not enough porosity to pass a reasonable amount of air through at any reasonable sized filter area. You'd probably need to make a couple of entire walls out of the stuff to get enough area to force enough air through at reasonable pressure to adequately ventilate a shelter.

Like a filter 8 feet high and 16 feet wide, maybe a half inch to a quarter inch thick, and maybe 3 or 4 PSI differential to force the air through, which means a lot of mechanical support, like a bazillion smaller panes supported by, say, steel beams, so the pressure doesn't just make it implode.

now I've got to do some more research on shale porosity when it's quarried unaltered from the ground.

I know that it metamorphoses under heat and pressure into slate, which is quite non-porous. They used it for some castle roofs all over Europe for many thousands of years. And it is used as pool table sub-surfaces, beneath the felt, because it's heavy and flakes off nice and smooth.

The outer walls and roof of my home are made of slate. The slate walls are about 1.5" in thickness and work great to keep the heat out or heat in. 

In the summer months, the outer walls are hot but the inner walls are still cool. Likewise, when we heat the inner house, the heat doesn't dissipate to the outer surface of the slate.

FWIW

I have a small water filter and it uses carbon. But it also leaves small particles in the water right after it’s changed out for a new one.

How does Japan have such a big supply of slate?

In short response: Nozawa Corporation

The longer reply is:

A very long answer to a simple question, LOL. If I understand correctly, it’s imported?

Well, initially, the discussion was that shale was used to create slate. But Japan improvised and used imported asbestos with a mixture of locally produced concrete to produce a new type of slate which didn't require shale which is hard to come by in Japan.

FWIW

Isn’t asbestos dangerous?

If it's used in a fibrous state (like they used to use for insulation) and it's allowed to decay (after 30 or 40 years), the fine particles that fray from it, if inhaled, can be carcinogenic. 

But they have come up with chemical compounds that, when mixed with concrete, can turn it into a solid hard slate (not fibrous) and which also has fire retardant properties as well. Suitable for outer walls and outer roofs of homes.

FWIW

So the slate is a fairly poor thermal conductor - or a reasonably good insulator.

If it wasn't so expensive, it might make a good material to work on hot materials over, if it doesn't spall from thermal shock if a little bit of molten metal were to splatter on it - like from cutting and welding above it.

But I know the stuff they use in pool tables is about 3/4 of an inch to about 1.25 inch thick and it's incredibly heavy. Back in college for a while I worked for an outfit that serviced pinball machines and pool tables. A pool table weighed at least 800 pounds. They were incredibly hazardous to handle on any kind of inclined surface for that reason - if one were in a proper dolly and it got away from you, it was as dangerous as a runaway car rolling down a hill.

We thus used power winches and lifting slings with all the care and safety protocols you would use operating a tow truck to load or unload a car.

The scariest job was when a pool table had to be brought up or down a flight of stairs, such as to a basement or 2nd story bar, as opposed to ground level. Most of the real work was preparing for the hoisting. We'd have to find something structurally solid enough to anchor the pulleys and line to at the top of the stairs. Then we'd lay 2x12 lumber on the stairs to make a ramp, with some cleats bolted to the underside to engage the stair treads.

Then we had to test the lifting line and pulleys and start the beast up the ramp. we tried to have a second safety line and a belay set up to a different part of the building structure. Sometimes we could open a window and put a steel beam outside that this was anchored to, so if something slipped the load couldn't just free-fall back down.

Only once it was solidly on a level floor could one really relax, then we'd just wheel it into position, and use the special pivoting part of the dolly to rotate the table from its side to upright since most stairwells are far too narrow to get a pool table up or down them while it's flat..

Last step was to use the dolly like a leveling jack. Retract all the leg adjustments, and slowly lower it with the scissors mechanism until the first leg touched the floor.

Lay a pair of levels on the surface at right angles to one another, and adjust the jack screws up or down to tilt the table until both bubbles were centered precisely.

Then finally you would extend the other leg screws until the weight transferred fully from dolly to floor, using a wrench to adjust the screw under load and keep the surface exactly level. Most floors were slightly uneven so you have to compensate.

Last step was, once you had a tiny bit of daylight between table and dolly, you go ahead and retract the scissors mechanism and slide the thing out from under the table, and roll the cage back to its side so you could get the dolly out of the bar or whatever.

It was doing a few of those installations that let me see the Smokeeters up close, including watching them be serviced to see how they worked.

And of course we had to clean up whatever we had rigged to get the table up / down the stairs.

Best scenario was a building with a big enough elevator to get table and dolly inside.

Usually, since ADA compliance was still a decade away or more, we had to usually go up or down a few steps even for a ground floor installation as that would never be at exactly the height of the sidewalk. Today, ,wheelchair ramps are perfect for moving very heavy objects. That saved the day about 4 years ago when I helped someone swap out some major components of a mainframe computer.

A hard drive about the size of a washing machine has 1/128th the capacity of the USB thumb drive in my pants watch fob pocket at the moment.