Hold old is the DAF? Possibly getting on a bit in which case it likely does have a clutch plate that contains asbestos. There is not much asbestos and there are lots of other things in clutch plates also some of the dust also comes from the flywheel face and the pressure plate which are both probably cast iron so black dust is typical.
Is it toxic? What do you mean by toxic? I would suggest stirring it up energetically with a compressed air blow gun in a closed space and then taking deep lung filling breathes is not a good idea. If you have inhaled trace amounts of the dust but were careful to avoid stirring it up you should not worry. I have worked on old vehicles, both clutch and brake linings, and never took much precaution regarding dust which I did blow of with an air gun and I was not worried then, which was over forty years ago, and I am still not worried. The hazard from asbestos dust was under-rated for many years but I think now sometimes it is over-rated. The people who did develop mesothelioma generally had been exposed to appreciable levels of the worst kind of asbestos for prolonged periods of time. Inadvertent short term exposure to low levels should be avoided but if it occurs it is no reason to get concerned.
As per usual you are the proverbial well of useful information.
Its a 2005 model. We have a good turnover due to the nature of our business. Breakdowns can be a serious problem so can't afford bad old equipment (Not good for the image either ). Probably shouldn't have been acting the maggot and spreading it on each other but not too much dust created!
Just a comment, that is in addition to the one that you would not last long as a manager with me , I think clutch plates now that don't contain asbestos have things like glass fibers, graphite and some metals but I don't know what else in detail. Probably in twenty years time it will be discovered that finely groung glass fibers are just as bad as asbestos fibers.