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A man wearing a life jacket, with another life jacket hanging at the lower left.

A personal flotation device (abbreviated as PFD; also referred to as, lifejacket, life preserver, Mae West, life vest, life saver, cork jacket, life belt, flotation suit, etc.) is a device designed to assist a wearer, either conscious or unconscious, to keep afloat with his or her mouth and nose (airway) of his or her head's face above the water surface when in or on water.

Devices designed and approved by authorities for use by civilians (recreational boaters, sailors, canoeists, kayakers, etc.) differ from those designed for use by passengers and crew of aircraft (helicopters, airplanes) and of commercial vessels (tugs, passenger ferries, cargo ships). Devices used by military (air force, special forces, marines, navy, coast guard) and police and enforcement agencies generally have features not found on civilian or commercial models, for example compatibility with other worn kit (e.g. survival vest, bullet proof vest / body armor, equipment harness, rappelling harness, parachute) and use of ballistic nylon cloth to protect pressurized carbon dioxide (CO2) canisters used for inflating the vest from injuring the wearer if struck by a round from a firearm. The ballistic cloth keeps the fragments from the canister from becoming shrapnel injurious to the user.

PFDs are available in different sizes and different designs purposed for various levels of protection.

The University of Victoria in British Columbia (province) Canada pioneered research and development into the "Floater Coat" (patented UVic Thermo Float PFD), which provides superior protection from cold water immersion (immersion hypothermia) through the incorporation of a neoprene rubber "diaper" that seals the user's upper thigh/groin region from otherwise cold, flushing and debilitating water.

Contents

Design(s)

Lifejackets or life vests are mandatory on airplanes travelling over water (in which case they consist of a pair of air cells (bladders) that can be inflated by triggering the release of carbon dioxide gas from a canister - one canister for each separate cell. Or the cells can be inflated "orally" that is by blowing into a flexible tube with a one-way valve to seal the air in the cell. Lifejackets must also be supplied on seafaring vessels, accessible to all crew and passengers and to be donned in an emergency.

Floatation devices are also found in near water-edges and at swimming pools. They may take the form of a simple vest, a jacket, a full-body suit (one piece coverall), or their variations suited for particular purposes. They are most commonly made of a tough synthetic fiber material encapsulating a source of buoyancy, such as foam or a chamber of air, and are often brightly colored as yellow or orange to maximize visibility for rescues. Some devices consist of a combination of BOTH buoyancy foam and an air chamber. Retroreflective "SOLAS" tape is often sewn to the fabric used to construct lifejackets and PFDs to facilitate a person being spotted in darkness when a search light is shone towards the wearer.

Types

Foam core

A foam core life vest

The simplest and least buoyant of the class come in the form of nylon-lined foam vests, often used in training for swimming, or as light safety precautions in relatively safe environments, such as lake cruises and amusement parks. With no need for a leakproofing quality check because of their inherently buoyant foam cores, they can be mass-produced inexpensively and widely used, making it the most commonly seen form of lifejackets.

Such devices can be best thought of as "buoyancy aid" only (as opposed to a 'life saver") in the sense that they are useful adjuncts for users who know how to swim. Non-swimmers (or weak swimmers) with no or little in-water orientation skills such as treading water and somersaulting would be disadvantaged wearing a simple buoyancy aid vest compared to an able competent swimmer who is capable of orienting him or herself in the water with his/her face clear of the water. It is possible to float in a face down in the water position while wearing such a vest.

Some foam core life vests are designed specially for children. These vests feature an understrap designed to be worn between the legs of the wearer to keep the vest from riding up when worn in the water, and possibly the wearer from completely slipping out of the life vest. The strap is adjustable and should be sized to fit sungly between the wearer's legs, tight enough to hold the life vest low on the wearer so they are not choked by the vest rising up because of its buoyancy, but loose enough so the wearer may swim comfortably, not feeling constrained by the vest. This strap is included life vests designed to be worn by 30 - 60 pound children and on some vests designed to be worn by people 60 - 90 pounds well. Other life vests feature harness-like straps designed to be worn between the legs, like a rockclimbing harness. These straps, similar to the single understrap, provide assistance to restrict the vest from riding up when worn in the water, and can be found on life vests designed to suit any age. Life vests designed for children include a headrest flap that helps support the head and keep it out of the water. A grab handle is attached to the headrest to if needed, resuce or lift the wearer up, or simply to carry the vest itself.

Air chambers

The red life jacket is an example of an air chamber vest.

Life jackets for outfitting large commercial transport in potentially dangerous waters, such as coastal cruises and offshore passages, and overwater air flights, are often a pair of (twin or double) sealed air chambers constructed of coated nylon (sometimes with a protective outer encasing of heavier, tougher material such as vinyl), joined together (but can also be constructed of foam aboard ships). Twin air chambers provide for redundancy in the event of one of the air chambers leaking, for example if the thin air cell fabric is sliced open by sharp metal fragments during emergency evacuation and egress.

Aircraft devices for crew and passengers are always inflatable since it may be necessary to swim down and away from a ditched or submerged aircraft: inflated or foam filled devices would significantly impede a person from swimming downward in order to escape a vehicle cabin. Upon surfacing, the person would then inflate the device, orally or by triggering the gas canister release mechanism.

"True" Life Jackets always provide more buoyancy than buoyancy aids[1] and the positioning of the buoyancy on the wearer's torso is such that a righting moment (rotational force) is developed that will eventually float most persons (for example unconscious) who are face down into a FACE UP attitude with their bodies inclined backward, unlike common foam buoyancy vests (which are simply swimmers' aids, really since they don't generate re-righting moment forces.) Self righting devices are be best for non-swimmers[2], who may not be able to orient themselves face up in the water, for example due to panic arising from finding themselves in deep, open water.

Today these air chamber vests are commonly referred to as "Inflatable Life Jackets or Vests" and are available not only for commercial applications but also for recreational boating, fishing, sailing, as well as kayaking and canoeing. They are available in a variety of styles and are generally more comfortable and less bulky than traditional foam vests.

The air chambers are always located over the breast, across the shoulders and encircling the back of the head. They may be inflated by either self-contained carbon dioxide cartridges activated by the pulling of a cord, or blow tubes with a one-way valve for inflation by exhalation. Some of the inflatable life jackets also react with the salt/fresh water, inflating them. The latest generation of self triggering inflation devices[3], however, respond to water pressure when submerged and incorporate an actuator known as a "hydrostatic release". Regardless of whether manually (pull cord) or automatically triggered, a pin punctures the cartridge/canister and the CO2 gas escapes into the sealed air chamber. However, there is a chance that these water pressure activated inflation devices do not inflate the lifejacket if a person is wearing waterproof clothing and falls into the water facedown. In these cases the buoyancy of the clothing can hold a person on the water surface and avoids the hydrostatic release. As a result a person can drown although the life jacket is fully functional. To be on the safe side, a pill activated inflation device should be preferred. A little pill that dissolves with water contact is in fact the safest option as it also works in shallow waters where the hydrostatic activator fails. This type of jacket is called an automatic[4]. As it is far more sensitive it is far more likley to activate during very heavy rain or spray. This could lead to an accident. Spare Co2 gas should always be carred.

Drifting in open seas and international waters, as encountered by long sea voyages and military forces, require prolonged survival in water. The life jackets suited for this purpose are often attached to a vest with pockets and attachment points for distress signaling and survival, for example: a handheld two-way radio (walkie-talkie), emergency beacon (406 MHz frequency), signal mirror, sea marker dye, smoke or light signal flares, strobe light, first-aid supplies, concentrated nutritional items, water purification supplies, shark repellent, knife, pistol.

Offshore sailors and others can utilize accessories such as leg straps to keep the inflated chambers in position for floating in a stable attitude and splash or face shields constructed of clear see-through vinyl which covers the head and face to ward off water from waves inundating the face (nasal and mouth entries to the airway).

Deep water

Livejacket from the disaster of MS Estonia

Some formats of PFDs are intended for long term immersion in cold water in that they provide insulation as well as buoyancy. While a wetsuit of neoprene rubber and divers' drysuits provide a degree of flotation, they are not formally considered by regulatory agencies as approved lifesaving devices or as PFDs, in most maritime countries. SCUBA divers commonly wear a "BC" or buoyancy compensator, which involves an inflatable gas chamber. The amount of gas can be increased or decreased to enable the diver to ascend, descend or maintain neutral buoyancy at a given water depth. Note that it is possible for an incapacitated person in the water to float face down while wearing simply a wet suit or a dry suit since they are not designed to serve as lifesaving devices in the normal use of that term.

A flotation device known as the Steinke hood is used as an escape device to ascend from a stranded submarine.

The Mark 10 Submarine Escape Immersion Equipment (SEIE) suit is intended to allow submariners to escape from much deeper depths than currently possible with the Steinke Hood. Some United States Navy submarines already have the system, with an ambitious installation and training schedule in place for the remainder of the fleet.

Because it is a full body suit, the Mark 10 provides thermal protection once the wearer reaches the surface, and the Royal Navy has successfully tested it at 180 m (600 feet) depths. (see Submarines in the United States Navy#Pressure and escape training and Steinke hood)

Underwater

Divers use buoyancy compensators to adjust their buoyancy while underwater and to provide positive buoyancy in an emergency to bring them to the surface or keep them at the surface.

Specialized

Specialized lifejackets can also be seen used in a myriad of environments. Shorter-profile vests are commonly used for kayaking (especially playboating), and high-buoyant types for river outfitters and other whitewater professionals. PFDs which include harnesses for tethered rescue work ('live-bait rescue') and pockets or daisy-chains for the attachment of rescue gear are made for swiftwater rescue technicians.

History

A "Mae West" life preserver.

The most ancient examples of "primitive lifejackets" can be traced back to inflated bladders of animal skins or hollow, sealed gourds, for support when crossing deeper streams and rivers.

Personal flotation devices were not part of the equipment issued to naval sailors up to the early 1800s, for example at the Napoleonic Battle of Trafalgar. Seamen who were press-ganged into naval service might have used such devices to jump ship and swim to freedom. It wasn't until lifesaving services were formed that personal safety of boat crews heading out in pulling boats generally in horrific sea conditions was addressed.

Purpose-designed buoyant safety devices consisting of simple blocks of wood or cork were used by Norwegian seamen. The modern lifejacket is generally credited to one Captain Ward, a Royal National Lifeboat Institution inspector in the United Kingdom, who, in 1854, created a cork vest to be worn by lifeboat crews for both weather protection and buoyancy.

The rigid cork material eventually came to be supplanted by pouches containing watertight cells filled with kapok, a vegetal material. These soft cells were much more flexible and more comfortable to wear compared with devices utilizing hard cork pieces. Kapok buoyancy was used in many navies fighting in the Second World War. Foam eventually supplanted kapok for "inherently buoyant" (vs. inflated and therefore not inherently buoyant) flotation.

Reference: Built for Life: the history of lifejackets; Dr. Christopher Brookes, Defence and Civil Institute for Environmental Medicine (Downsview , Ontario, Canada; Canadian Navy); Survival Systems (Halifax, Nova Scotia, Canada) [apparently the only authoritative text on the subject in the English language with a comprehensive account of lifejackets; the only others are in German] in 1878 they were called life belts

Mae West

The Mae West was a common nickname for the first inflatable life preserver, which was invented in 1928 by Peter Markus (1885-1974) (US Patent 1694714) with his subsequent improvements in 1930 and 1931. The nickname was originated due to the fact that someone wearing the inflated life preserver often appeared to be as physically-endowed as the actress Mae West. It was popular during the Second World War era with US and British Air Force servicemen who were issued inflatable Mae Wests.

References

  1. ^ Ten Newtons equals 1kg of flotation Guide to Choosing a lifejacket
  2. ^ non swimmers or unconscious person
  3. ^ Hammar Hydrostatic
  4. ^ Automatic lifejacket

See also

External links








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