Carbon Fiber Hazard
The problem with cf lies in its size, structure and molecular structure.
There was quite a bit of publicity some years back about using cf rovings to assist the "repair and healing" of damaged tendons in the legs and feet of racehorses. This use relied on the ability of cf fibres to encourage the development of (I think) collagen, and hence cartilage, structures along the fibres.
Certainly the medics believe the lump on my finger is gristle or cartilage in nature. And I am informed it is consistent with the kind of "growth" that cf generates.
Therefore, if a person breathes the dust from sanding cf (for example) some of those particles will have the basic (if only very small) characteristics of the cf fibres. If one of these lodges in lung tissue then I can imagine (just by looking at my finger) that it is going to cause severe problems in time.
How many have heard of asbestosis? Same principle, different substance. It is caused by the size and shape of the particles, not by the "chemicals", that make up the asbestos.
So, to repeat, it is not "carbon" that is "carcinogenic".
It is the size and structure of the particles that causes the problem.