Underwater construction work is an area, which requires extensive training. Not only does the worker need to worry about the regular dangers that come with working with tools, now he is working in a different medium, water, which has an affect on the work actually being done, plus he needs to use special breathing equipment.
Some of the work can be on bridges, power stations, ships, submarines, marinas, etc. And each type of job will have its own special requirements. Diving poses a unique risk, because if a problem arises the diverís life will be in immediate danger.
Compression & Decompression
The bends, also called decompression sickness. This is a condition where a diver rises too quickly. Nitrogen that is in his body, from breathing compressed air, needs time to leave the body. If this is not allowed then the diver can experience the bends. The only cure for this is a decompression chamber, which must be present whenever scuba work is being done. Warning signs are; sore joints, itchy skin, vision and hearing difficulty, paralysis, and death.The best way to prevent decompression sickness is to avoid diving too deep, do not stay deep above the recommended time, accend slowly with regular stops along the way, and limiting number of dives per day.
This is an affect similar to alcohol intoxication. This condition is caused because more gases are breathed, while underwater, from the oxygen supply. Because of the greater pressure, these gases are absorbed into the body easier than at sea level.
This is a condition where higher levels of oxygen are breathed. This has an affect on the body, and can result in; disorientation, trouble breathing, trouble with vision, lung damage, seizures, and death.
Construction Related Safety
Under water the laws of physics and chemistry function differently. This needs to be part of the training of anyone that will work underwater. Welding, for example, functions differently underwater. Chemicals react differently. The weight of objects is less and things move slower underwater.
No one should be attempting any underwater work unless they have been properly trianed. And proper training should be from a reputable certified school.