EPIRBs come in both automatically deployed or manually deployed models.
Category I EPIRBs are activated either manually or automatically. Category
I EPIRBs are housed in a bracket equipped with a hydrostatic release
that releases the EPIRB when the vessel sinks. The EPIRB is activated
when released and floats to the surface. An EPIRB thus released will
float free unless retrieved by survivors in the water or in a survival
craft. Category II EPIRBs are manual activation only units. Both categories
of EPIRBs are designed to activate when they are immersed in water, regardless
of the position of the manual switch.
EPIRBs must float with the antenna deployed and out of the water in
the normal transmitting position. U.S. regulation requires that they
be equipped with a strobe light that activates automatically when the
beacon is switched on. All have a means to tether the EPIRB to a vessel
or survival craft so they will float free while secured to the survival
craft. They must operate for at least 48 hours at either -40°C to
+55°C (Class 1) or -20°C to +55°C (Class 2). COSPAS-SARSAT
standards assume that the body of water in which the EPIRB is floating
will serve as the ground plane for the antenna.
PLBs are generally smaller because they require smaller batteries, being
required to operate for only 24 hours at either -40°C to +55°C
(Class 1) or -20°C to +55°C (Class 2). They are not required
to be equipped with a strobe light. All are currently equipped with a
tether of some sort, although this may just be a wrist tether. Category
1 PLBs must be buoyant; Category 2 PLBs are not buoyant. Category 1 PLBs
are not required to float in a transmitting position—they simply
are required not to sink, the objective being solely to help prevent
loss if dropped into the water. Howevr, they are not precluded from floating
in a transmitting position. PLBs are manually activated only.
It has been noted that in real survival situations many EPIRBs are retrieved
from the water after automatic release and activation or are retrieved
from the vessel by survivors when they abandon ship into a life raft.
In either case the EPIRB is then retained inside the life raft, rather
than being floated in the water on the end of their very thin tether
line, as designed. In some cases this appears to be the result of ignorance
as to how to deploy the EPIRB as designed. In other situations, it appears
that as their primary hope for rescue, survivors do not appear to be
willing to trust their life to that thin tether, particularly in severe
conditions. In a number of documented cases, the tether line was not
securely tied off to the life raft and was separated from the life raft.
Since they will tend to drift at different rates, they can quickly become
separated. At least one life raft manufacturer, in recognition of this,
provides an option for a secure pocket in the life raft to hold the EPIRB.
(NOTE: Some aviation life rafts come equipped with an ELT (aviation version
of an emergency beacon) that is secured semi-permanently in the raft,
and some also activate the ELT automatically upon deployment of the raft.)
In recognition of this reality, we tested EPIRBs both floating tethered
to a vessel and retained inside a life raft.
PLBs were tested on land, held by persons floating in the water (or
simulation of same) and in the life raft.
