Under what conditions is Tayammum allowed and how is it performed?

Tayammum is permitted when water is not available within a distance of approximately one mile, or if using water will cause or worsen a disease, or if there is danger in reaching the water (e.g., a dangerous animal or enemy). Method of Tayammum: 1. Make the intention (Niyyah) for purification. 2. Strike both hands on clean earth, blow off excess dust, and wipe the entire face. 3. Strike the hands again on the earth and wipe the right arm including the elbow with the left hand, and then wipe the left arm including the elbow with the right hand. Ensure the spaces between the fingers are also wiped (Khilal). The earth used must be clean and of the nature of the earth (dust, sand, stone, or lime).