<P> Diatoms should normally never be present in human tissue unless water was aspirated, and their presence in tissues such as bone marrow suggests drowning, however, they are present in soil and the atmosphere and samples may easily be contaminated . An absence of diatoms does not rule out drowning, as they are not always present in water . A match of diatom shells to those found in the water may provide supporting evidence of the place of death . Drowning in salt water can leave significantly different concentrations of sodium and chloride ions in the left and right chambers of the heart, but this will dissipate if the person survived for some time after the aspiration, or if CPR was attempted, and have been described in other causes of death . </P> <P> Most autopsy findings relate to asphyxia and are not specific to drowning . The signs of drowning are degraded by decomposition . Large amounts of froth will be present around the mouth and nostrils and in the upper and lower airways in freshly drowned bodies . The volume of froth is generally much greater in drowning than from other origins . Lung density may be higher than normal but normal weights are possible after cardiac arrest reflex or vaso - vagal reflex . The lungs may be over inflated and waterlogged, filling the thoracic cavity, and the surface may have a marbled appearance, with darker areas associated with collapsed alveoli interspersed with paler aerated areas . Fluid trapped in the lower airways may block the passive collapse that is normal after death . Haemorrhagic bullae of emphysema may be found . These are related to rupture of alveolar walls . These signs, while suggestive of drowning, are not conclusive . </P> <P> Most drowning is preventable . It has been estimated that more than 85% of drownings could have been prevented by supervision, training in water skills, technology, regulation and public education . </P> <P> Many pools and designated bathing areas either have lifeguards, a pool safety camera system for local or remote monitoring, or computer - aided drowning detection . However, bystanders play an important role in drowning detection and either intervention or the notification of authorities by phone or alarm . </P>

When is a drowning victim especially a child in cooler water considered dead