

Re: other shapes, they have to be tesselations of repeating regular polygons. I would refuse to call the one on the right a grid:

And this one is right out:

Edit: I have been informed that the Escher tesselation pictured is in fact a grid and am now in a foul mood.










If one shingle breaks yeah you wouldn’t want to huff it, but realistically dilution would mean the tiny amount released is next to harmless. Asbestos is an extreme occupational hazard for people unlucky enough to have worked with it, but for most extant asbestos material the best practice is to leave in place.