There are two separate issues buried in the question of chalk dust safety. In one sense, the main ingredients of chalk dust are considered to be non-toxic, which simply means they do not pose a threat when ingested. In another sense, chalk dust can and does accumulate in the human respiratory system, which means it can create long-term health problems due to overexposure. In short, swallowing a piece of white chalkboard chalk won't kill you, but breathing in chalk dust for a number of years can create or trigger respiratory problems.

Chalk dust is the natural by-product of using a chalk crayon on a blackboard. As the chalk is scraped across the rough surface of the chalkboard, particles of chalk dust are sent out into the surrounding air. Some of this chalk dust settles to the ground or is ventilated outside, but much of it falls on clothing, furniture, electronic equipment and shelves. Teachers and students also inhale a portion of this chalk dust, which usually becomes trapped in the mucus layers of the throat and upper lungs.

A small amount of respirated chalk dust is not considered harmful. Those with healthy respiratory systems can expel the chalk dust through coughing, and the remaining material should be absorbed safely into the body. For those with chronic breathing issues such as asthma, however, exposure to chalk dust can trigger a reaction. In fact, many school systems strongly urge teachers to move students with respiratory problems away from the chalkboard area. Chalkboards, trays and erasers filled with chalk dust should also be cleaned regularly.

Standard chalk for classroom use is generally made from calcium carbonate, a processed form of natural limestone. The traditional method of creating white chalk was to form a clay-like paste with the calcium carbonate and allow it to cure in chalk-shaped molds. This chalk worked well with slate chalkboards, but it also generated a significant amount of chalk dust that floated into the surrounding air. Teachers who used traditional chalk for a number of years developed some respiratory problems, although not generally considered severe.

There is now a product called dustless chalk, designed to address the chalk dust issue. Instead of forming chalk crayons through individual molds, the new chalk mixture is extruded into ropes, then cut to size and allowed to dry. This dustless chalk does generate a form of chalk dust, but the particles are much heavier and tend to fall directly to the floor instead of floating in the air. Exposure to airborne chalk dust has been reduced, but the accumulation of chalk dust elsewhere is still problematic.

Beyond the human health aspects of chalk dust exposure, there are also potential electronic hazards. Devices such as computers and digital versatile disc (DVD) players stored inside classrooms can suffer damage from accumulated chalk dust. As the dust particles circulate throughout the room, cooling fans may draw them into the computers' inner workings. As dust builds up on the motherboard and other heat-sensitive parts, the risk of overheating increases. Chalk dust can also cause severe damage to sensitive electronics, such as the laser reader of a DVD player or the playback heads of a video cassette recorder (VCR).

Chalk dust is considered an irritant and an occupational hazard by a number of occupational safety organizations around the world. If you must work around chalk dust for extended periods of time, many safety experts suggest using a filtered mask over your mouth and nose and taking a number of breaks in a fresh air environment. Use other dustless methods of communication, such as dry erase boards or overhead projectors, whenever possible.