Thermal stress occurs when the difference between the water and body temperature
is large enough that the body will gain heat (hyperthermia) or lose heat
(hypothermia). In both conditions mild exposures will lead mainly to discomfort,
but one must always be aware of the signs and symptoms of more severe stress. In
these cases, either proper protective equipment should be worn, or exposure
limited.
Hyperthermia is related to a rise in body core temperature. Divers
are susceptible to heat stress when their thermal garment sufficiently insulates
their body from the water and they are unable to dissipate their body heat.
Members of the dive team who are not in the water are more likely to suffer heat
injury. The treatment of all cases of hyperthermia shall include cooling of the
victim to reduce core temperature.
In mild to moderate cases of hyperthermia (heat
exhaustion), the victim will complain of frontal headache, nausea, weakness,
excessive fatigue, and/or dizziness. If these symptoms occur, the dive supervisor
will be notified. Cooling should be started immediately by spraying with water
and fanning. Oral fluid replacement should begin as soon as the victim can drink
and continue until he has urinated pale to clear urine several times. If the symptoms
do not improve within 5 minutes, the victim shall be evaluated by Diving
Medical Personnel.
In severe cases of hyperthermia (severe heat exhaustion or
heat stroke), the victim will experience disorientation, tremors, loss of consciousness
and/or seizures. This is a medical emergency. If these symptoms occur, the
dive supervisor shall be notified. Cooling measures shall be started and the victim
shall be transported immediately to a medical treatment facility.
Cold water or ice should never be used on the whole body
because this will cause vasoconstriction which decreases blood flow to the skin,
which may slow the process of lowering core temperature. Ice packs to the neck,
armpit or groin may be used. The most efficient means of cooling is achieved by
removing all clothes, spraying the victim with a fine mist of lukewarm-to-cool
water, and then fanning.
Immersion hypothermia is a potential hazard whenever diving
operations take place in cool to cold waters. A diver’s response to immersion in
cold water depends on the degree of thermal protection worn and water temperature.
The signs and symptoms of falling core temperature are given in Table 3-1
(Chapter 3). Responses to falling core temperature are individual.
To treat hypothermia, rewarm the victim. In mild cases, the
victim will experience uncontrolled shivering, slurred speech, imbalance, and/or
poor judgment. If these symptoms occur, the dive supervisor shall be notified
immediately. Passive and active rewarming measures should be initiated and
continue until the victim is sweating. If the victim requires more than a few
minutes of rewarming, he shall be evaluated by Diving Medical Personnel.
Severe cases of hypothermia are characterized by loss of
shivering, decreased consciousness, irregular heartbeat, and/or very shallow pulse
or respirations. This is a medical emergency. Avoid any exercise, keep the victim
lying down, initiate only passive rewarming, and immediately transport to the
nearest medical treatment facility.
CAUTION Do not institute active rewarming with severe cases of hypothermia.
WARNING CPR should not be initiated on a severely hypothermic diver unless it
can be determined that the heart has stopped or is in ventricular
fibrillation. CPR should not be initiated in a patient that is breathing.
1. Passive:
-
Remove all wet clothing.
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Wrap victim in a blanket (preferably wool).
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Place in an area protected from wind.
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If possible, place in a warm area (i.e. galley).
2. Active:
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Warm shower or bath.
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Place in a very warm space (i.e. engine room).
In addition to hypothermia,
other responses to exposure to cold water create potential hazards for the diver.
The effect of these responses may be cumulative and magnified by underlying
hypothermia.
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Diving Reflex/Bradycardia. The Mammalian or diving reflex, which is caused
by either sudden exposure of the face to cold water or immersion of the whole
body in cold water, can result in bradycardia (slowing of the heart rate),
peripheral vasoconstriction, and increased blood supply to the brain and heart.
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Laryngeal Stimulation. Inhaling a small amount of water can induce spasm of
the laryngeal muscles and possibly cause airway obstruction.
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Carotid Sinus Reflex. External pressure on the carotid artery from a tight
fitting neck dam, wet suit, or dry suit can activate receptors in the arterial wall,
causing a decrease in heart rate with possible loss of consciousness. Using an
extra-tight-fitting dry or wet suit or tight neck dams to decrease water leaks
increase the chances of activation of the carotid reflex and the potential for
problems.
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Breath Holding and Bradycardia. Breath-hold diving causes a decrease in
heart rate to approximately 60–70 percent of predive levels and an increase in
the incidence of cardiac arrhythmia (irregular heartbeat). Exposure to cold
water also exacerbates the degree of bradycardia. It is unknown whether the
bradycardia and arrhythmias associated with removing or losing a face mask
contribute to diving casualties. It is reasonable that when operationally
required, such as during buddy breathing or an underwater dive rig switchover,
the “breathholding” diver should be closely monitored by the unaffected
dive buddy.
Emergency medical training should emphasize emergency procedures as outlined
for treating an unconscious diver on the bottom (see paragraph 19-5.2), treating a
diver who has nearly drowned (see paragraph 19-6), treating a hypothermic diver
(see paragraph 19-7.2), and the material covered in this section
