When you cut carbon it is essential that you wear a filter that ensures you don't breathe fine carbon shards. They don't dissolve in you lungs, but wander through your body, possibly doing serious damage to your tissues. Also, you should do it in a space where there is lots of air exchange so you can be confident that when you remove the filter there are no shards floating in the air. Finally, wear gloves, because you may inadvertently push shards that settle on your hands into your skin. I still have shards that work their way out of my skin several years after I stopped working on carbon fiber!