Table 8. Disabling agents associated with 175 fatal snorkelling incidents .

78 (45%) Medical
mean (SD) age 59 (15), 91% male
ischaemic heart disease	20 (12%) Unconsciousness (laryngospasm?)
pre-existing arrhythmia	mean (SD) age 46 (19), 75% male
cardiac abnormality
subarachnoid haemorrhage
23 (13%) Environmental
mean (SD) age 41 (14), 100% male
adverse conditions	9 (5%) Buoyancy
marine animal/boat injury	mean (SD) age 37 (14), 100% male
entrapment
21 (12%) Apnoeic hypoxia	24 (14%) Unknown
mean (SD) age 28 (5), 95% male	mean (SD) age 47 (16), 88% male