Who, What, Why: How long can someone survive in a life raft? Who, What, Why

The Magazine answers the questions behind the news Published duration 20 May 2014

A search has been resumed for four British men lost in the Atlantic Ocean. How long is it possible to survive at sea in a life raft, or in the water?

There are extraordinary tales of survival in life rafts. The record-holder is Poon Lim, who survived 133 days on a raft after his ship was torpedoed by a U-boat in 1942. Another well-known case is that of the family of Dougal Robertson who spent 38 days in a raft after their yacht sank.

But Mike Tipton, professor of human and applied physiology at Portsmouth University, points out that lengthy life raft survival episodes almost always take place near the equator where the water is warm. The water where the Cheeki Rafiki yacht is understood to have got in trouble - between Cape Cod in Massachusetts, and the Azores, in the North Atlantic - is much colder, perhaps about 15C. And the weather was bad.

When people are plunged into a cold sea they suffer from cold-water shock, says Pip Hare, coastal safety manager at the Royal National Lifeboat Institution and an ocean racer. Death can be rapid . "Anything below 15C has an immediate impact on the body - higher blood pressure, increased breathing rate. It incapacitates even fit people who are good swimmers."

Launching a life raft in a controlled fashion means the situation is better. But in cold and choppy seas it is still extremely difficult to survive for any length of time. "You can very quickly become physically incapacitated. If you are in a life raft in these conditions, the chances of it being dry or well insulated [are small]," says Tipton. Immersed to the waist in water, hypothermia can kill relatively quickly - assuming that the raft isn't swamped to the point where the occupants drown.

Tipton says survivors have a "hierarchy of needs":

Air

Viable circulation in the body

Suitable temperature

Fluid

Food

media caption What is inside a life raft?

"In the best possible scenario if they are in a life raft and there are frequent rain showers [for drinking water] you can go many, many days," says Tipton. "If you are in freezing cold water and your raft is being swept and flooded then it's hours rather than days."

The US Coastguard was criticised by some for initially calling off the search after 20 hours, but Tipton concurs with the experts who say that if a life raft was launched it would probably have been found by searchers, not least because a location beacon would have been activated. The US Coastguard's computer modelling of drift would have let them search in roughly the right areas. In the event someone ends up in cold water with no raft, the prospects are considerably grimmer. In temperatures of 15C, survival beyond six hours would be extremely unlikely.

A typical 24-hour emergency pack

Two parachute flares , two hand flares , a radar signal reflector, a buoyant smoke flare , a whistle , a mirror and instructions for signalling for help

, two , a a , a , a and instructions for signalling for help Water supply

A repair kit , a hand pump , a torch , spare bulb and batteries , two paddles , rescue quoit and line, two drogues (a funnel-shaped device deployed to help control the craft) and 30m of line

, a , a , spare , two , and line, two (a funnel-shaped device deployed to help control the craft) and 30m of line Bailers (for bailing out water) and two sponges for drying the raft

(for bailing out water) and two for drying the raft Survival instructions , a floating safety knife

, a Sea sickness bags and anti-sea sickness tablets

and Thermal protective clothing

First aid kit

Source: Ocean Safety