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in seawater or when it is exposed to extremely cold air
temperatures. If multiple dives are planned, postpone freshwater
rinsing of the regulator until all the day’s dives are completed.
Drysuit fabric (vulcanized rubber, crushed neoprene
or trilaminate) depends on the diver’s preference, the
requirements for range and ease of motion and the available
options. The choice of drysuit underwear is perhaps more
important than the choice of drysuit material because it is
the underwear that provides most of the thermal protection.
Many divers wear an under layer of expedition-weight
polypropylene and an outer layer of 400g Thinsulate®.
Drygloves or mitts with inner liners (rather than wetgloves)
are most commonly used with drysuits. Diving Unlimited
International (DUI) zipseal drygloves see widespread use since
they effectively permit the warm air that surrounds the rest of
the body to also reach the hands at depth. Two disadvantages
of dryglove systems are the complete lack of thermal
protection if the gloves flood or are punctured and the related
risk of flooding the entire drysuit.
Because a drysuit must be inflated to prevent suit squeeze
with increasing pressure, it is most efficient to regulate
buoyancy at depth by controlling the amount of air in the
drysuit, which must be equipped with a hands-free exhaust
valve. BCDs are considered emergency equipment to be
used only in the event of catastrophic drysuit failure. This
procedure eliminates the need to vent two air sources during
ascent, reduces the chance of BCD-inflator free flow and
simplifies the maintenance of neutral buoyancy during the
dive. The main purpose of air in a drysuit, of course, is to
provide thermal insulation.
Divers must wear sufficient weight to allow for maintenance
of neutral buoyancy with a certain amount of air in the
drysuit. Runaway negative buoyancy is as great a safety
problem as an out-of-control ascent. Because of the amount
of weight commonly worn (30 to 40 pounds) and the serious
consequences of accidental release, weight harnesses are
favored over weight belts.
Hazards and Emergencies
Extreme underwater visibility may make objects appear closer
than they are; this illusion could entice divers to travel farther
from the access hole than is prudent. The greatest hazard
associated with fast-ice diving is the potential loss of the
dive hole. Access holes, leads and cracks in the ice are often
highly visible from below because daylight streams through
them. However, dive holes may be difficult to see due to low
light or from the holes being covered with portable shelters.
Therefore, a well-marked down line is required for fast-ice
dives. Divers should maintain positive visual contact with
the down line during the dive and take frequent note of their
position relative to the access hole or lead. Problems requiring
an emergency ascent are serious, since a vertical ascent to the
surface is impossible except when a diver is directly under the
dive hole or lead.
Pack ice is inherently unstable and its conditions can
change rapidly, primarily from surface wind conditions. An
offshore wind may blow pack ice away from the shoreline
and loosen the pack, whereas an onshore wind may move
significant quantities of pack ice against shorelines or fast-ice
edges, obstructing what may have been clear access areas
when divers entered the water.
As with diving in general, the best approach to ice-diving
emergencies is prevention. Divers must halt operations any
time they become unduly stressed because of cold, fatigue,
unease or any other physiological reason. Similarly, terminate
the dive in the event of equipment difficulties such as free-
flowing regulators, tether-system entanglements, leaking
drysuits or buoyancy problems.
To clearly mark access holes, divers deploy well-marked
down lines, establish recognizable landmarks (such as specific
ice formations) under the hole at the outset of dives, leave a
strobe light, flag or other highly visible object on the bottom
just below the hole or shovel surface snow off the ice in a
radiating spoke pattern that points the way to the dive hole.
Physiological Considerations
Cold is the overriding limiting factor for dive operations,
especially with regard to the thermal protection and dexterity
of hands. Dives should be terminated before a diver’s hands
become too cold to effectively operate gear or grasp a down
line. This loss of dexterity can occur quickly (within 5 to 10
minutes if hands are not adequately protected). Holding onto
a camera will increase the rate at which a hand becomes cold.
Switching the housing from hand to hand or attaching it to the
down line may allow hands to rewarm. DUI dryglove systems
have greatly improved thermal protection of divers’ hands.
Heat loss occurs through inadequate insulation, exposed
areas (such as the head in an insufficient hood arrangement)
and from breathing cold air. Scuba-cylinder air is initially at
Courtesy Michael Lang