Carbon paper allows those marking on it to make a copy onto another piece of paper below. Impressions made on the surface of the carbon paper will make identical marks on whatever is under it. However, the resulting carbon dust poses a number of different health and fire hazards that people should be aware of.
Carbon paper is very flammable, as both carbon dust and paper are combustible. Carbon paper must be thrown away in a responsible fashion. Placing disposed sheets of carbon paper in a fire-safe wastebasket, all to themselves, is a good idea. Carbon dust is also flammable, and enough of it in the air could cause a small explosion. If in doubt, be sure to open windows in the room or run a fan to clear any dust out.
Skin and Respiratory Problems
Dust from carbon paper is not only flammable, it can also cause respiratory problems if inhaled. This will only occur if the room is not well-ventilated, and a lot of carbon paper is being used; even so, it is wise not to inhale carbon dust if it can be avoided. If a large amount of carbon gets onto the skin, it can also cause itching and a painful rash. Wearing gloves and long sleeves are a good way to protect yourself from having skin breakouts.
Working extensively with carbon paper can cause you to ingest a small amount, if it gets on your hands. When you eat a meal, or put your hands about your mouth for some reason, it can result in stomach and digestive problems. Wearing gloves and long sleeves can keep this from happening. You should also wash your hands after using carbon paper extensively.