There are two separate issues buried in the question of chalk dust safety. In one sense, the main ingredients of this dust are considered to be non-toxic, which simply means they do not pose a threat when ingested. In another sense, this material 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 a person, but breathing in the 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 board, particles of it are sent out into the surrounding air. Some of this 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 as well, which usually becomes trapped in the mucus layers of the throat and upper lungs.
A small amount of inhaled dust is not considered harmful. Those with healthy respiratory systems can expel it through coughing, and the remaining material should be absorbed safely into the body. For those with chronic breathing issues such as asthma, however, exposure 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 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 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 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 dust, but the particles are much heavier and tend to fall directly to the floor instead of floating in the air. Exposure to airborne particles has been reduced, but the accumulation of 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 dust. As the chalk particles circulate throughout the room, cooling fans may draw them into the computers' inner workings. As it builds up on the motherboard and other heat-sensitive parts, the risk of overheating increases. This 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. People who must work around it for extended periods of time may want to use a filtered mask over the mouth and nose and taking a number of breaks in a fresh air environment. They should also use other dustless methods of communication, such as dry erase boards or overhead projectors, whenever possible.