That was a concern from the 90's. However you are being exposed to the "nano particles" everyday already. Rubber from car tires decomposes on the highway into particles of the scale that they can be considered "nano particles", for example. When ever you drive on the highway, you're stirring up clouds of them.

While the general nano particle fear is a little extreme, some of the structures (specifically carbon nano-tubes) have a similar shape as Asbestos, which does cause cancer due to it's shape.

CNTs aren't graphine, and I'm not sure that graphine can be easily made into tubes, but it still should give some pause for thought.

Just wanted to second this: I don't think we know enough about how safe these things are. It's very different to have something like graphene packaged up in a computer chip vs. free-floating in the air. I also have no idea if common, off-the-shelf respirators are effective at blocking such small particles.

Also worth bearing in mind is that, I believe, wherever you make one form of carbon you'll probably end up making other forms too, e.g. buckyballs (C60) and carbon nanotubes have both been found in soot. So even if graphene is safe, I have no idea if this process will produce other potentially unsafe things too. A friend is actually working on looking at the effect carbon nanotubes have on lung epithelial cells, so I know there's interest there.

That said, I imagine you'd find all these products in a standard wood fire too, but then I recall reading that smoke from wood fires is as bad or worse for you as cigarette smoke so perhaps that's little comfort...

Note: I am not a doctor and not an expert in this field either.

Eh, do it in your shed, and use an affordable respirator (available at any hardware store). If you have a place where you can make a bit of a mess then the cost of safety gear is low, construction-grade stuff will be adequate for most non-biological use cases. You can get special filters for asbestos, lead, and similar hazardous substances which contractors encounter frequently in old houses.

The main obstacle I see here (based on this report) is uncertainty about how to separate the material after you've blended it and what exactly you can apply it to without adding lots of expensive lab equipment. One candidate that springs to mind is using it for printing circuits, given graphene's high conductivity.

Silver is probably a better material for a conductive glue than graphene. Probably even aluminium is better.

Random chuncks of graphene thrown toguether, touching in random directions aren't a good conductor at all.