diving before travelling to altitude – DCS can occur without flying if the person moves to a high-altitude location on land immediately after diving, for example, scuba divers in Eritrea who drive from the coast to the Asmara plateau at 2,400 m (7,900 ft) increase their risk of DCS. diving at altitude – diving in water whose surface pressure is significantly below sea level pressure — for example, Lake Titicaca is at 3,800 m (12,500 ft). Versions of decompression tables for altitudes exceeding 300 m (980 ft), or dive computers with high-altitude settings or surface pressure sensors may be used to reduce this risk. Individual
The following individual factors have been identified as possibly contributing to increased risk of DCS:

dehydration – Studies by Walder concluded that decompression sickness could be reduced in aviators when the serum surface tension was raised by drinking isotonic saline, and the high surface tension of water is generally regarded as helpful in controlling bubble size. Maintaining proper hydration is recommended. There is no convincing evidence that overhydration has any benefits, and it is implicated in immersion pulmonary oedema. patent foramen ovale – a hole between the atrial chambers of the heart in the fetus is normally closed by a flap with the first breaths at birth. In about 20% of adults the flap does not completely seal, however, allowing blood through the hole when coughing or during activities that raise chest pressure.
Reduction in decompression requirements can also be gained by breathing a nitrox mix during the dive, since less nitrogen will be taken into the body than during the same dive done on air.Following a decompression schedule does not completely protect against DCS. The algorithms used are designed to reduce the probability of DCS to a very low level, but do not reduce it to zero. The mathematical implications of all current decompression models are that provided that no tissue is ingassing, longer decompression stops will decrease decompression risk, or at worst not increase it. Efficient decompression requires the diver to ascend fast enough to establish as high a decompression gradient, in as many tissues, as safely possible, without provoking the development of symptomatic bubbles. This is facilitated by the highest acceptably safe oxygen partial pressure in the breathing gas, and avoiding gas changes that could cause counterdiffusion bubble formation or growth. The development of schedules that are both safe and efficient has been complicated by the large number of variables and uncertainties, including personal variation in response under varying environmental conditions and workload, attributed to variations of body type, fitness and other risk factors. Exposure to altitude
One of the most significant breakthroughs in the prevention of altitude DCS is oxygen pre-breathing.