Commercial diving involves a diverse group of individuals and companies involved in a wide range of activities. These workers are exposed to the same hazards anyone would if they spent extended periods of time underwater, such as drowning, respiratory and circulatory problems, and hypothermia. The number of dives, length of time spent underwater, lack of visibility, and the strenuous nature of the task increase the risk of this type of activity. Additionally, commercial divers are often exposed to construction or demolition type hazards such as cutting, welding, material handling, cleaning, operation of heavy equipment, and general work with power tools.