According to the relevant departments of the Ministry of Education to the national part of the survey data show that the teacher's occupational disease rate has been increasing year, the trend of diversification of occupational diseases, including dust-induced pneumoconiosis and a variety of acute and chronic respiratory diseases in China's current teacher's occupational disease is the most important, the most serious and The prevalence of myopia in students also increased year by year, to the degree of abnormal severity.
Chalk from its chemical composition, the main ingredients are calcium carbonate (limestone) and calcium sulfate (gypsum), a small amount of calcium oxide and other small metal elements such as iron, cadmium, etc., even if the improvement of the original chalk on the market is the dust-free chalk, but in the original chalk to add grease or alcohol-like substances as adhesives, Then add the larger proportion of raw materials, so that the proportion of chalk and volume are increased, not easy to fly, but in practical application is not obvious. With the chemical acidity of chalk as a weak alkaline substance, from its physical properties namely chalk in writing and chalk erase process of its main chemical composition, concentration, dispersion, gravity, shape, hardness, solubility, etc., in the whole teaching process produced a large amount of dust, long floating in the air, serious pollution of indoor air, Endangering the physical and mental health of teachers and students, the harm of modern teaching aids such as slide projector, projectors, computers and laboratories and other important equipment, affecting the performance of these equipment, the use of quality and life. At the same time, because of the large amount of use, it is necessary to mining a large number of limestone, ore and gypsum mines, which will cause environmental pollution and ecological damage.
In addition to the students because of long-term blackboard white, black and white, as well as classroom dust pollution caused by the problem of myopia research data show: China's 1992 data compared with 1980 similar data, 10 years 22 provinces (cities, Autonomous Region) The average pupil's eyesight decline rate rose by 23.45%, at present, our country pupil low eyesight rate reaches 21.91%, middle school students is 55.86%, high school students is 75.79%, the university student is close to 80%, each year is rising trend.