Hi ​@Lee1234,

Welcome to the Dyson Community, and thanks for your question.

The size of the fibres means that in the unlikely event that they become airborne, they are too big to pose any danger as they aren’t respirable - so can’t get into the part of the lungs where any risk would potentially exist.

Like any Dyson machine, accessory or component, the anti-static carbon fibre filaments within our brush bars have been rigorously assessed for safety, and for this health risk specifically. The brush bar only spins when the main suction motor is running, so any fibres which happen to become loose would be contained within the machine's filtration system - again, this is highly unlikely. 

All Dyson cord-free vacuums include anti-static carbon fibre filaments as part of their brush bar design, whereas current Dyson corded upright vacuums do not.

My concern is about the micron sized particles given off by abrasion of the brush bar roller, not whole fibres (the stuff is spinning on hard floors) and those particles will find their way deep into your lungs. Granted, most of them will travel into the machine and be trapped by the hepa filter, but who knows what the numbers are. I’d love see the analysis. People who work with carbon fiber wear respirators and whole body suits. The particulates are not unlike asbestos. Even touching carbon fiber dust is to be avoided (hence the warning in your docs). Why do it? It just seem crazy, but I could be overstating the risk. Probably driven by marketing.