The dangers of chalk: chalk Environmental friendly, but chalk harmful! The fine particles of chalk strong germs adsorption ability, the composition of the chalk is an alkaline substance. Harmful bacteria, alkaline substances on the teachers and students of the respiratory system, skin, ear, nose, throat, likely to cause inflammation, dry, atrophy, itching, chapped, lung cancer, emphysema and kidney damage. Students and from morning to night in the classroom responsible for the effaceurs task, the greater the health hazards of underage students chalk dust less resistance.

Dust pollution is a direct threat to the lives of people, especially living in the environment of dust pollution will cause a variety of cardiovascular and respiratory diseases. Asthma, bronchitis incidence constantly in this year's rapid increase in a typical manifestation of increased dust pollution the chemical composition of the dust pollution for the elderly, the children, the greatest impact. dust, which can directly determine harmful levels of dust on the human body, for example, containing free silica dust, also known as silica dust can cause silicosis, the higher the amount of silicon-containing the greater the harm to individuals; lead, manganese the toxic substances dust can cause the poisoning of the corresponding category; case of cotton, hemp, organic dust grains, can cause pharyngitis, bronchitis and allergic reactions. smaller dust particles in the air floating time is longer, the more chances of being inhaled. the general dust particles of 5 microns or less, to reach the deep lung, causing lung disease i.e. pneumoconiosis. the chalk mass is too small, the role of air can not ignored. We study diffusion of chalk to draw the following four phenomena:
 

1. When the chalk dust early speed, height, a certain resistance to airflow chalk dust diffusion distance is inversely proportional to the quality of the reduction with chalk dust, that is, the larger the mass, the landing point farther. However,