A personal flotation device (PFD; also referred to as a life jacket, life preserver, life belt, Mae West, life vest, life saver, cork jacket, buoyancy aid or flotation suit) is a flotation device in the form of a vest or suite that is donned and fastened to a user to prevent the wearer from drowning in a body of water. The device will keep the wearer afloat with his/her head and mouth above the surface – he/she does not have to swim or tread water in order to stay afloat and can even be unconscious.
Unlike other flotation devices, a PFD is fastened to the user and does not need to be actively held onto; this prevents a wearer who is either in the water or falling into the water from losing her grip on the flotation and subsequently becoming immersed in the water leading to drowning. The fastening of the device also allows it to be comfortable when worn in the water and allows for wearer to swim or propel her/himself with all limbs. For these reasons PFD's are the most common and widely used form of flotation device.
PFDs are commonly worn on small watercraft or other locations where accidental entry into deep water may occur in order to provide immediate support for the wearer should they end up in the water. PFDs are also kept on large vessels for passengers to wear in an emergency in order to help them stay afloat should they be forced to enter the water or accidentally fall overboard during an evacuation. PFD's are commonly worn for swimming and/or other activities that require an individual to be in the water. This is for reasons such as safety (to prevent the drowning of weak swimmers, swimmers in dangerous conditions or swimmers far from safety), to make swimming easier and less demanding, to allow someone who is unable to swim to safely enter water, or as assistance for activities such as water skiing.
PFDs are available in different sizes to accommodate variations in body weight. Designs differ depending on wearing convenience, the activities and conditions they are designed to be used in and the level of protection the wearer needs. There are three main types of PFDs: life jackets, buoyancy aids and survival suits; PFDs are most often constructed out of foam pieces, with the exception of some life jackets which are inflated with air. Other highly specialized forms of PFDs include buoyancy compensators used for scuba diving, and submarine escape devices.