One type of respiratory hazard involves airborne particles consisting of dusts, fumes, and mists. Dusts are a combination of materials created through actions such as sweeping, drilling, or sawing. This is common in areas where construction is taking place. This is similar to fumes which are produced in the process of heating and cooling solid materials. This can also occur when certain chemicals are mixed together. Mist are microscopic droplets commonly created in spraying. Another respiratory hazard encountered in the work place is when one finds themselves in an oxygen-deficient atmosphere. The normal oxygen level in an environment is 20.9%. OSHA classifies an oxygen-deficient area as having less than 19.5% oxygen.