na as above a hoover or stand the other side of thw outlet and wear a mask.Just gave the grinder another go, apart from the dust it's the best of my options today I think, have you got a dust bag attached to your saw Dan?
But m class Hoover will save your lungsAfter a bit of searching i found this, bit cheaper than an m class hoover, its from Hardie boards, had it years,
I'd do it this way. Use a blade with high tooth countBest way is to use a circular saw set to very shallow depth, say about 5mm then use the cut as a score and snap the board.