Food Grade Diatomaceous Earth, which is primarily composed of amorphous silica, is safe for use around the house, the garden and as a dietary supplement. It is, however, made up of very fine particles that become easily suspended in the air and can cause the same sort of lung irritation that any other household dust might cause. If you are working with Food Grade DE for a prolonged period of time, in a confined space or if you are just particularly sensitive to airborne dust, you should wear a mask or a respirator while working.
Pool or Filter Grade Diatomaceous Earth is very dangerous if inhaled because it contains a high percentage of crystalline silica. Crystalline silica can lodge in your lungs and cause permanent damage, has been shown to cause the disease Silicosis and is considered carcinogenic.