Drowning is a type of suffocation, known as asphyxia, caused by the lungs filling with water. The lungs are designed to get oxygen from the air to major organs. But, with water blocking the oxygen exchange, a drowning victim quickly goes unconscious and dies within minutes.

• Fast Fact: more than 80 per cent of drowning victims are males, often between the ages of 15 and 44.
  

The brain uses a significant amount of the body’s oxygen — about 20 per cent — so it is very sensitive to oxygen loss. Once a person’s oxygen supply is cut off, brain cells begin to starve and die. After four minutes without oxygen, permanent brain damage starts to occur. After about six minutes, the brain is dead — and so is the person.

Some people have also been known to die up to 48 hours after a near-drowning, in a condition known as “secondary drowning”. When a near-drowning happens, victims breathe some water into their lungs. This water can dilute the surfactants in the lungs which help to keep our air sacs (alveoli) open and working. As a result, fluids from the blood accumulate in the damaged areas — much in the same way your finger swells up with fluid after you injure it by slamming it in a door or hitting it with a hammer. These fluids prevent the transfer of oxygen into the blood and death can result. For this reason, every person who has had a near-drowning should see a doctor.

• .Fast Fact: As little as a tablespoon of water in the lungs can cause secondary drowning.
  

However, under some circumstances, people can survive for extended periods of time under water. A phenomenon known as mammalian diving reflex allows people (particularly young children) who have been suddenly submerged in freezing water below 0 degrees Celsius to survive for up to an hour without any real damage. Basically, the body goes into “energy saving mode” by slowing down the heart beat and not circulating valuable oxygenated blood to less important appendages. Once the victim is returned to warmer temperatures, all systems start functioning normally and the person is often fine.

Don’t let this article keep you away from the beach this summer, though! Just remember to be smart and safe when you’re in the water. Always go swimming with a friend. This way you’ll have help nearby if you get a cramp or get tired. Swim in safe areas that are supervised by lifeguards and know your limits – if you’re not a strong swimmer, stay in shallower water where your feet can touch the ground. If you are a strong swimmer, keep an eye out for those friends who might not be. For more information and tips about water safety, visit kidshealth.org.

Learn More!

Life Saving Society Drowning Fact Sheet
http://www.vancouversun.com/news/reduce+Canada+drowning+toll/3312820/story.html
http://www.emedicinehealth.com/drowning/article_em.htm

http://divingindepth.com/mammalian-diving-reflex/
http://www.memorylossonline.com/glossary/hypoxiaanoxia.html
http://www.sutcliffe.ca/joel/nls/drowning.pdf