|
| "Inflatable"
versus "inherently buoyant" lifejacket"? |
| The
current European Standards differentiate buoyancy aids and lifejackets
by their buoyancy force Newton (N). All materials of lower weight
than water produce buoyancy. Closed cell foams of polyvinyl chloride
(PVC) or polyethylene (PE) are used for buoyant material. (SECUMAR
uses SECUMAR SOFT foam). Atmospheric
gas or others as carbon dioxyd (CO2) or nitrogen (N2
), produce the inflatable buoyancy.
CO2 has proved to be adequate because of its properties
of being non-toxic, non-inflammable, and because it can be stored
in small disposable cylinders. |
|
| A
little lesson on physics ... |
| Anyone
floating in the water requires a minimum of buoyancy force to keep
his head on the water surface as well as to turn his body to keep
his nose and mouth above the surface. The distance from water surface
to the mouth is called "freeboard",
and this distance may be influenced by the clothes worn. An undressed
adult will achieve this freeboard with a buoyancy of 100 Newton
(N); (10 N = 1 daN = DecaNewton equal to 1 kp. As a safety margin
and to ensure turning of the unconscious wearer by the lifejacket,
150 N is required. An inherently buoyant lifejacket of this buoyancy
would be much too bulky. |
|
| Comfort
or discomfort for the wearer ... |
| The
correct form of lifejacket is essential. It would be just a compromise
to try to maintain the freeboard and turning property by reducing
the buoyancy to a certain extent. It can be achieved by the design
of chest buoyancy chambers and collars in the category 100 N. However,
this design is hardly suitable for inherently buoyant material because
the greater buoyancy becomes too bulky. And, the permanent wearing
of bulky inherently buoyant lifejackets is unacceptable. |
|
| The
"inflatable" means a small pack. |
| Only
the inflatable lifejacket supplies sufficient buoyancy in the 150
and 275 N categories. The deflated buoyancy chamber is just a small
pack and offers comfort of wear. The inflator (manual or automatic)
can be activated any time. The lifejacket can be combined with other
life saving appliances such as a safety harness. |
|
| ‘To
be on the safe side ...’ |
| Inflatable
and inherently buoyant lifejackets are genuine alternatives. The
inherently buoyant jacket will never lose its airtightness, does
not require maintenance at regular intervals, cannot activate inadvertently
if in contact with water, and is less expensive. The decision, however,
should be made subject to the range of application as defined in
the European Standards. If the wearer is exposed to rough sea, foul
weather, wearing foul weather clothing, and wants to be on the safe
side, he will decide on the inflatable lifejacket. |
