Devices are available in adult and child sizes.
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Some flotation devices are small snazzy vests, and others are bulky and very serious looking. This is due to the different materials used in their construction and also the potential function of the devices. The additional buoyancy provided by flotation devices is potentially lifesaving, so it is important that people use the water wear the device that suits their activities.
The basic physics behind flotation devices is that they add buoyancy to the person using them in the water. When a person is in the water, there is an upward force acting on them from the water and a downward force from the weight of the person. If the person floats, the downward force is less than the upward force from the water, and that person is buoyant. Different types flotation devices provide different levels of buoyancy, measured as the force in pounds it adds to a user's personal buoyancy.
Types of Flotation Devices
Flotation devices are split in different groups by their potential uses. Type I devices are lifejackets for use offshore and are designed to hold a person face up even if they are unconscious. Type II, near-shore buoyant vests, are for use inshore but some brands also turn people face up. The flotation aid Type III is only for use in calm water and are not capable of turning the wearer face up. The major difference between the first three types is that the bulk of the device, with the offshore device (Type I) being the most bulky as it requires the most buoyancy. The near-shore device is less bulky as it requires less buoyancy, and the Type III flotation aid is generally very neat and comfortably shaped for freedom of movement as it is often worn in watersports. Type IV are devices that are designed to be thrown to a person in the water, like a buoyancy ring. Special use devices are another type of flotation device and include items like deck suits. Inflatable life jackets are the final group of flotation devices.
Various materials can increase the buoyancy of a person. Foam is common in flotation devices and can be made from natural or synthetic substances. A type of plastic called PVC-foam, a material called Gaia made from nitrile compounds, and Kapok, a fiber from the kapok tree, are all types of stuffing used. Inflatable flotation devices use air to add buoyancy, and hybrid devices use both foam and air.
Differences in Buoyancy
According to the Personal Flotation Device Manufacturers Association, most adults only need 7 to 12 extra pounds of buoyancy for safety. Each type of flotation device has a specific level of buoyancy, which reflects its potential uses and the potential risks the person wearing it faces. Type I devices provide 22 pounds of extra buoyancy, and special use devices can also provide this much. Type II and III both provide 15.5 pounds, and the Type IV throwable devices vary in buoyancy. The hybrid inflatable jackets vary from 7.5 pounds to as much as 22 pounds.
Many flotation devices are inherently buoyant; their materials do not need any adjustment when the person hits the water. The inflatable or hybrid inflatable flotation devices, on the other hand, need to inflate when the person enters the water. Some types contain disposable bobbins or cartridges, which dissolve on contact with water and allow a firing mechanism to be activated. The firing process may be automatic or controlled manually by the wearer. Inflatable devices are also equipped with valves that allow the wearer manually to inflate the device.