Decompression sickness and arterial gas embolism in recreational diving are associated with certain demographic, environmental, and dive style factors. A statistical study published in 2005 tested potential risk factors: age, gender, body mass index, smoking, asthma, diabetes, cardiovascular disease, previous decompression illness, years since certification, dives in the last year, number of diving days, number of dives in a repetitive series, last dive depth, nitrox use, and drysuit use. No significant associations with risk of decompression sickness or arterial gas embolism were found for asthma, diabetes, cardiovascular disease, smoking, or body mass index. Increased depth, previous DCI, larger number of consecutive days diving, and being male were associated with higher risk for decompression sickness and arterial gas embolism. Nitrox and drysuit use, greater frequency of diving in the past year, increasing age, and years since certification were associated with lower risk, possibly as indicators of more extensive training and experience. Environmental
The following environmental factors have been shown to increase the risk of DCS:

the magnitude of the pressure reduction ratio – a large pressure reduction ratio is more likely to cause DCS than a small one. repetitive exposures – repetitive dives within a short period of time (a few hours) increase the risk of developing DCS. Repetitive ascents to altitudes above 5,500 metres (18,000 ft) within similar short periods increase the risk of developing altitude DCS. the rate of ascent – the faster the ascent the greater the risk of developing DCS.
Hangmans fracture is the colloquial name given to a fracture of both pedicles, or partes interarticulares, of the axis vertebra (C2). Causes
The injury mainly occurs from falls, usually in elderly adults, and motor accidents mainly due to impacts of high force causing extension of the neck and great axial load onto the C2 vertebra. In a study based in Norway, 60% of reported cervical fractures came from falls and 21% from motor-related accidents. According to the Agency for Healthcare Research and Quality (AHRQ), the group under the highest risk of C2 fractures are elderly people within the age group of 65-84 (39.02%) at risks of falls (61%) or motor accidents (21%) in metropolitan areas (94%). There were 203 discharges from the age group 1-17; 1,843 from 18- to 44-year-olds; 2,147 from 45- to 64-year-olds, 4,890 from 65- to 84-year-olds, and 3440 from 85+-year-olds. Females accounted for 54.45% of occurrences while males accounted for the other 45.38%. Mechanisms
The mechanism of the injury is forcible hyperextension of the head, usually with distraction of the neck. Traditionally this would occur during judicial hanging, when the noose was placed below the condemned subjects chin. When the subject was dropped, the head would be forced into hyperextension by the full weight of the body, a sufficient force to cause the fracture.