CHAPTER 19 — Diving Disorders Not Requiring Recompression Therapy 19-1
This chapter covers diagnosis and treatment of diving disorders for
which recompression therapy usually is not required. It is important to realize that
this chapter is a working document. While you should adhere to the procedures as
closely as possible, any mistakes or discrepancies shall be brought to the attention
of NAVSEA immediately. There are instances where clear direction cannot be
given; in these cases, contact the diving medical experts at NEDU or NDSTC for
This chapter is a reference for individuals trained in diving procedures. It
is also directed to users with a wide range in medical expertise, from the fleet diver
to the Diving Medical Officer. Certain treatment procedures require consultation
with a Diving Medical Officer for safe and effective use. In preparing for any
diving operation, it is mandatory that the dive team have a medical evacuation
plan and know the location of the nearest or most accessible Diving Medical
Officer and recompression chamber. Diving Medical Personnel should be
involved in predive planning and in training to deal with medical emergencies.
Even if operators feel they know how to handle medical emergencies, a Diving
Medical Officer should be consulted whenever possible.
All members of the dive team shall be constantly alert for signs and symptoms of
oxygen deficiency (hypoxia), carbon monoxide poisoning, carbon dioxide toxicity
(hypercapnia), oxygen toxicity, nitrogen narcosis, labored breathing (dyspnea),
and hyperventilation.
Oxygen Deficiency (Hypoxia).
Oxygen deficiency, or hypoxia, if not corrected
promptly, leads to loss of judgment, unconsciousness, and even death. There is no
reliable warning of the onset of hypoxia. If hypoxia develops gradually, symptoms
of interference with brain function will appear. Symptoms of hypoxia include:
Lack of concentration
Lack of muscle control
Inability to perform delicate or skill-requiring tasks
Loss of consciousness
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Causes of Hypoxia.
The most common cause of hypoxia is an interruption of the
breathing gas supply. This situation is obvious, and is treated by immediately
reestablishing the gas supply, or shifting to an alternate gas supply. Shifting the
diver to a gas with insufficient oxygen can also cause hypoxia. Analysis of diving
accidents caused by divers breathing insufficient oxygen indicates that the first
sign of trouble is an unresponsive diver. The immediate cause of the problem
usually is not obvious. Always know the oxygen content of the diver’s breathing
gas! If a diver becomes unresponsive during a mixed-gas dive, hypoxia should be
assumed until it is ruled out.
Treating Hypoxia.
To begin immediate treatment for hypoxia:
If the diver is in the water, shift to an alternate gas supply containing sufficient
Administer 100 percent oxygen at the surface.
If the diver has lost consciousness or appears abnormal in any way, seek med-
ical advice immediately.
Unconsciousness Due to Hypoxia.
Because the first sign of hypoxia may be
unconsciousness, it may be difficult to differentiate hypoxia from arterial gas
embolism in an ascending diver. However, recompression treatment for arterial
gas embolism should also correct the hypoxia.
Treating Hypoxia in Specific Operational Environments.
Refer to Volume 4 for
information on treatment of hypoxia arising in specific operational environments
for MK 16 dives and diving involving closed-circuit oxygen rebreathers.
Carbon Monoxide Poisoning.
Carbon monoxide poisoning can result from an air
supply contaminated by exhaust fumes. It is treated the same way as low oxygen
content of breathing gas. The early signs of carbon monoxide poisoning are:
Vo m i t i n g
Divers with these symptoms can be treated with 100 percent oxygen at the surface.
Divers with symptoms (i.e. severe headache, mental status changes, any neurolog-
ical symptoms, rapid heart rate) should be treated at 60 fsw on oxygen. When
carbon monoxide poisoning is suspected, isolate the suspect breathing gas source,
and forward gas samples for analysis as soon as possible.
Carbon Dioxide Toxicity (Hypercapnia).
Carbon dioxide toxicity, or hyper-
capnia, may occur with or without a deficiency of oxygen. The diver may have no
warning of hypercapnia and may become confused and even slightly euphoric
before losing consciousness. The inspired carbon dioxide itself does not usually
cause permanent injury. Injury from hypercapnia is usually due to secondary
effects such as drowning or injury caused by decreased mental function or uncon-
CHAPTER 19 — Diving Disorders Not Requiring Recompression Therapy 19-3
sciousness. Because the first sign of hypercapnia may be unconsciousness and it
may not be readily apparent whether the cause is hypoxia or hypercapnia, rule out
hypoxia first.
Causes of Carbon Dioxide Buildup.
Carbon dioxide buildup can be caused by:
Inadequate ventilation of UBAs
Controlled or skip-breathing
Excessive breathing resistance
Excessive dead space in equipment such as a failure of mushroom valves in
scuba mouthpiece
Failure or expenditure of the carbon dioxide absorbent material in a closed-
circuit or semiclosed-circuit UBA
Treating Hypercapnia.
To treat hypercapnia, lower the inspired carbon dioxide
level by:
Increasing helmet ventilation
Decreasing the level of exertion
Shifting to an alternate breathing source
Aborting the dive if defective equipment is the cause
Divers surfacing unconscious should be treated for suspected arterial gas
Treating Hypercapnia in Specific Operational Environments.
Refer to Volume 4
for information on treatment of hypercapnia in specific operational environments
for MK 16 diving operations and diving involving closed-circuit oxygen
Oxygen Toxicity.
Oxygen toxicity affects the lungs (Pulmonary Oxygen
Toxicity) or the central nervous system (CNS Oxygen Toxicity). Pulmonary
oxygen toxicity may occur during long oxygen exposures such as recompression
treatments, special 100-percent oxygen UBA operations, and saturation dives.
Refer to paragraph 21- for information on pulmonary oxygen toxicity.
Central Nervous System (CNS) Oxygen Toxicity.
During in-water diving opera-
tions, the most common and most serious form of oxygen toxicity involves the
central nervous system (CNS). The symptom of CNS oxygen toxicity that has the
most serious consequence is the oxygen convulsion. The convulsion itself is not
harmful and there will be no long-term residual effects provided injury or
drowning can be prevented.
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Symptoms of CNS Oxygen Toxicity.
CNS oxygen toxicity is usually not encoun-
tered unless the partial pressure of oxygen approaches or exceeds 1.6 ata.
However, oxygen convulsion may be encountered at lower oxygen partial pres-
sure. Symptoms of CNS oxygen toxicity may occur singly or together, in no
particular order. There may be no warning of an impending convulsion. Signs and
symptoms of CNS oxygen toxicity include:
Visual symptoms. Tunnel vision, a decrease in diver’s peripheral vision, and
other symptoms, such as blurred vision, may occur.
Ear symptoms. Tinnitus is any sound perceived by the ears but not resulting
from an external stimulus. The sound may resemble bells ringing, roaring, or
a machinery-like pulsing sound.
Nausea or spasmodic vomiting. These symptoms may be intermittent.
Twitching and tingling symptoms. Any of the small facial muscles, lips, or
muscles of the extremities may be affected. This is the most frequent and
obvious symptom.
Irritability. Any change in the diver’s mental status, including confusion,
agitation, and anxiety.
Dizziness. Symptoms include clumsiness, incoordination, and unusual
Convulsions. The first sign of CNS oxygen toxicity may be a convulsion
that occurs with little or no warning.
Treating a Tethered Diver.
A tethered diver who thinks he has symptoms of
oxygen toxicity shall inform the Diving Supervisor. The Diving Supervisor shall
take action to lower the oxygen partial pressure by:
Decreasing diver depth 10 feet.
Discontinuing 100 percent oxygen and vent with a gas of lower oxygen
Treating a Free-Swimming Diver.
Free-swimming divers on a 100-percent
oxygen UBA shall alert their diving partner and surface if possible.
Treatment for CNS Convulsions.
If a diver convulses, the UBA should be venti-
lated immediately with a gas of lower oxygen content, if possible. If depth control
is possible and the gas supply is secure (helmet or full face mask), the diver’s
depth must be kept constant until the convulsion subsides. If an ascent must take
place, it should be done as slowly as possible. A diver surfacing unconscious
because of an oxygen convulsion or to avoid drowning must be treated as if
suffering from arterial gas embolism. Convulsing divers in the recompression
chamber should be protected from physical harm. When the convulsion subsides,
the diver should be kept with head back and chin up to ensure an adequate airway
until consciousness is regained. Forcing the mouth open to insert a bite block is
CHAPTER 19 — Diving Disorders Not Requiring Recompression Therapy 19-5
unnecessary. CNS oxygen toxicity occurring during recompression therapy is
discussed fully in paragraph 21-
Treating CNS Oxygen Toxicity in Specific Operational Environments.
Refer to
Volume 3 for information about treatment of CNS oxygen toxicity in specific
operational environments for surface-supplied helium-oxygen diving, and to
Volume 4 for MK 16 diving operations and 100-percent oxygen rebreather dives.
Nitrogen Narcosis.
Narcosis is a state of stupor or unconsciousness caused by
breathing inert gases at pressure while diving. The most common form, nitrogen
narcosis, is caused by breathing compressed air at depth.
Symptoms of Nitrogen Narcosis.
Symptoms of nitrogen narcosis may occur
singly or together, in no particular order. Signs and symptoms include:
Loss of judgment or skill
A false feeling of well-being
Lack of concern for job or safety
Apparent stupidity
Inappropriate laughter
Tingling and vague numbness of lips, gums, and leg
Treatment of Nitrogen Narcosis.
The only effective way to counteract the
narcotic effect of nitrogen is to lower the nitrogen partial pressure. Specifically:
The diver should ascend or be brought to a shallower depth.
If mental acuity is not restored, the dive shall be aborted.
Nitrogen Narcosis in MK 16.
When diving MK 16 UBA (maintaining a constant
of 0.75) with N
as the diluent, nitrogen narcosis becomes a significant
factor at deep depths.
Hyperventilation is rapid breathing in excess of metabolic
requirements, usually as the result of a conscious voluntary effort or by apprehen-
sion. Hyperventilation excessively lowers the carbon dioxide levels in the blood
and increases the blood oxygen level slightly. This, in turn, may lead to a
biochemical imbalance that gives rise to dizziness and twitching or tingling of the
extremities, which may be mistaken for CNS oxygen toxicity. Usually, this
twitching is also accompanied by some degree of spasm of the small muscles of
the hands and feet which allows a sure diagnosis to be made. Treatment is to slow
down the breathing rate by direction and reassurance, which allows the condition
to correct itself. Refer to Chapter 3 for more information on the signs, symptoms,
and treatment of hyperventilation.
Shortness of Breath (Dyspnea).
The increased density of the breathing gas at
depth, combined with physical exertion, may lead to shortness of breath that may
become severe and cause panic in some divers.
19-6 U.S. Navy Diving Manual—Volume 5
Dyspnea is usually associated with carbon dioxide buildup in the body, but may
occur without it. When dyspnea occurs, the diver must rest until the shortness of
breath subsides. This may take several minutes. If dyspnea does not subside with
rest, or if it returns with even slight exertion, it may be due to carbon dioxide
buildup. In open-circuit UBAs, ventilation rates should be checked to make sure
they are adequate; the helmet should be ventilated if necessary. Adequate ventila-
tion rates are at least 4 acfm for moderate work and 6 acfm for very hard work.
Ventilation should not drop below 1 acfm, even at rest.
In demand systems, excessive dead space from a damaged oral-nasal may be the
cause. In closed or semiclosed UBAs, the CO
absorbent canister may be spent. If
these causes are likely, the dive must be aborted to correct them.
Pulmonary overinflation syndromes are disorders that are caused by gas
expanding within the lung. The disorders encountered in diving are arterial gas
embolism, mediastinal and subcutaneous emphysema, and pneumothorax.
Normally, only arterial gas embolism (AGE) requires recompression therapy
(Chapter 20, paragraph 20-2).
Mediastinal and Subcutaneous Emphysema.
Mediastinal emphysema is caused
by gas expanding in the tissues behind the breast bone. Symptoms include mild to
moderate pain under the breast bone, often described as a dull ache or feeling of
tightness. Deep inspiration, coughing, or swallowing makes the pain worse, and
the pain may radiate to the shoulder, neck or back.
Causes of Subcutaneous Emphysema.
Subcutaneous emphysema results from
movement of the gas from the mediastinum to the region under the skin of the
neck and lower face. Mild cases are often unnoticed by the diver. In more severe
cases, the diver may experience a feeling of fullness around the neck and may
have difficulty in swallowing. The diver’s voice may change in pitch. An observer
may note a swelling or apparent inflation of the divers neck. Movement of the
skin near the windpipe or about the collar bone may produce a cracking or
crunching sound (crepitation).
Treatment of Mediastinal and Subcutaneous Emphysema.
Suspicion of medias-
tinal or subcutaneous emphysema warrants prompt referral to medical personnel
to rule out pneumothorax. Treatment of mediastinal or subcutaneous emphysema
with mild symptoms consists of breathing 100 percent oxygen at the surface. If
symptoms are severe, shallow recompression may be beneficial. Recompression
should only be carried out upon the recommendation of a Diving Medical Officer
who has ruled out the occurrence of pneumothorax. Recompression is performed
with the diver breathing 100 percent oxygen and using the shallowest depth of
relief (usually 5 or 10 feet). An hour of breathing oxygen should be sufficient for
resolution, but longer stays may be necessary. Decompression will be dictated by
the tenders decompression obligation. The appropriate air table should be used,
but the ascent rate should not exceed 1 foot per minute. In this specific case, the
CHAPTER 19 — Diving Disorders Not Requiring Recompression Therapy 19-7
delay in ascent should be included in bottom time when choosing the proper
decompression table.
A pneumothorax is air outside the lung that is trapped in the chest
cavity. This condition can result from a severe blow to the chest or a rupture of
lung tissue due to overpressurization.
Symptoms of Pneumothorax.
Pneumothorax is usually accompanied by a sharp
unilateral (one side) pain in the chest, shoulder, or upper back that is aggravated
by deep breathing. To minimize the pain, the victim will often breathe in a
shallow, rapid manner. The victim may appear pale and exhibit a tendency to bend
the chest toward the involved side. A collapsed lung may be detected by listening
to both sides of the chest with the ear or a stethoscope. A completely collapsed
lung will not produce audible sounds of breathing. In cases of partial pneu-
mothorax, however, breath sounds may be present and the condition must be
suspected on the basis of history and symptoms. In some instances, the damaged
lung tissue acts as a one-way valve, allowing gas to enter the chest cavity but not
to leave. Under these circumstances, the size of the pneumothorax increases with
each breath. This condition is called tension pneumothorax. In simple pneu-
mothorax, the respiratory distress usually does not get worse after the initial gas
leakage out of the lung. In tension pneumothorax, however, the respiratory distress
worsens with each breath and can progress rapidly to shock and death if the
trapped gas is not vented by inserting a catheter, chest tube, or other device
designed to remove gas from the chest cavity.
Treating Pneumothorax.
Mild pneumothorax can be treated by breathing 100
percent oxygen. Cases of pneumothorax that demonstrate cardiorespiratory
compromise may require the insertion of a chest tube, large-bore intravenous (IV)
catheter, or other device designed to remove intrathoracic gas (gas around the
lung). These devices should only be inserted by personnel trained in their use and
the use of other accessory devices (one-way valves, underwater suction, etc.)
necessary to safely decompress the thoracic cavity. Divers recompressed for treat-
ment of arterial gas embolism or decompression sickness, who also have a
pneumothorax, will experience relief upon recompression. A chest tube or other
device and a one-way relief valve may need to be inserted at depth to prevent
expansion of the trapped gas during subsequent ascent. If a divers condition dete-
riorates rapidly during ascent, especially if the symptoms are respiratory, tension
pneumothorax should always be suspected. If a tension pneumothorax is found,
recompression to depth of relief is warranted to relieve symptoms until the
thoracic cavity can be properly vented. Pneumothorax, if present in combination
with arterial gas embolism or decompression sickness, should not prevent imme-
diate recompression therapy. However, a pneumothorax may need to be vented as
described before ascent from treatment depth.
Prevention of Pulmonary Overinflation Syndrome.
The potential hazard of the
pulmonary overinflation syndromes may be prevented or substantially reduced by
careful attention to the following:
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Medical selection of diving personnel, with particular attention to eliminating
those who show evidence of lung disease or who have a past history of
respiratory disorders. Divers who have had a spontaneous pneumothorax have
a high incidence of recurrence and should not dive. Divers who have had
pneumothorax from other reasons (e.g., surgery, trauma, etc.) should have
their fitness for continued diving reviewed by an experienced Diving Medical
Officer, in consultation with appropriate respiratory specialists.
Evaluation of the divers physical condition immediately before a dive. Any
impairment of respiration, such as a cold, bronchitis, etc., may be considered
as a temporary restriction from diving.
Proper, intensive training in diving physics and physiology for every diver, as
well as instruction in the correct use of various diving equipment.
Barotrauma, or damage to body tissues from the mechanical effects of pressure,
results when pressure differentials between body cavities and the hydrostatic pres-
sure surrounding the body, or between the body and the diving equipment, are not
equalized properly. Barotrauma most frequently occurs during descent, but may
also occur during ascent.
Squeeze during descent occurs when gas in a cavity is compressed. The
types of squeeze most frequently encountered in diving are:
Middle ear squeeze is the most common form of barotrauma, caused by a
blocked or dysfunctional eustachian tube or from improper equalization. This
will cause immediate pain—which becomes progressively worse as the
eardrum stretches—and possibly vertigo, hearing loss, and tinnitus. If descent
is continued without equalizing the pressure, the eardrum may eventually
rupture. If this occurs the pain will immediately disappear, but nausea and
vertigo may result from cold water entering the middle ear.
External ear squeeze is caused by a hood or other piece of equipment covering
the external ear passage. This may result in the same symptoms as a middle-
ear squeeze.
Sinus squeeze is caused by blocked passages that vent the sinuses to the upper
respiratory air passages.
Lung (thoracic) squeeze is caused by compression of air in the lungs to a
volume less than residual volume. This could happen in a breathhold.
Whole body squeeze can occur when the air supply in a dry suit fails to balance
water pressure. This could be precipitated by a sudden or unexpected increase
in depth, by malfunctioning or maladjusted supply and exhaust valves, or by
the absence or failure of the safety non-return valve.
CHAPTER 19 — Diving Disorders Not Requiring Recompression Therapy 19-9
Face mask squeeze can occur when the diver fails to equalize air in the mask
by nasal exhalation. In a full face mask, malfunctioning air supply or valving
can cause face mask squeeze.
Suit squeeze is caused by a pocket of air in a dry suit that becomes trapped
under a fold or fitting and pinches the skin in the fold area.
Tooth squeeze is caused by a pocket of air in a filling.
Treating Squeeze During Descent.
To treat squeeze during descent:
Stop descent.
If efforts to equalize pressure fail, ascend a few feet.
Avoid clearing on ascent.
Avoid a forceful Valsalva
If further efforts to equalize pressure fail, abort the dive.
If the diver reports dizziness, ventilate the diver, abort the dive, and evaluate
the need to send down the standby diver to assist.
Report the squeeze to the medical personnel trained in diving medicine for
appropriate treatment.
Treating Reverse Squeeze During Ascent.
Reverse squeeze occurs when gas
trapped in a cavity cannot escape as it expands during ascent. To treat reverse
squeeze of the middle ear or sinus during ascent:
Stop ascent and, if clearing does not occur spontaneously, descend 2 to 4 feet.
Ascend slowly and in stages to allow additional time for equalization.
Avoid forceful Valsalva.
Evaluate the need to send down the standby diver to assist if difficulty persists.
Vertigo may develop.
Upon surfacing, report the problem to the medical personnel trained in diving
medicine for appropriate treatment.
Preventing Squeeze.
Sinus and ear squeeze are best prevented by not diving with
nasal and sinus congestion. If decongestants must be used, check with medical
personnel trained in diving medicine to obtain medication that will not cause
drowsiness and possibly add to symptoms caused by the narcotic effect of
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Refer to Chapter 3 for more information on the signs and symptoms of the
various types of squeeze.
Gastrointestinal Distention as a Result of Gas Expansion.
Divers may occasion-
ally experience abdominal pain during ascent because of gas expansion in the
stomach or intestines. This condition is caused by gas being generated in the intes-
tines during a dive, or by swallowing air (aerophagia). These pockets of gas will
usually work their way out of the system through the mouth or anus. If not, disten-
tion will occur.
Treating Intestinal Gas Expansion.
If the pain begins to pass the stage of mild
discomfort, ascent should be halted and the diver should descend slightly to
relieve the pain. The diver should then attempt to gently burp or release the gas
anally. Overzealous attempts to belch should be avoided as they may result in
swallowing more air. Abdominal pain following fast ascents shall be evaluated by
a Diving Medical Officer.
Preventing Intestinal Gas Expansion.
To avoid intestinal gas expansion:
Do not dive with an upset stomach or bowel.
Avoid eating foods that are likely to produce intestinal gas.
Avoid a steep, head-down angle during descent to minimize the amount of air
Ear Barotrauma.
Simple ear squeeze is discussed in paragraph 19-4.1. More
serious forms of ear barotrauma are rupture of the eardrum or round or oval
Eardrum Rupture.
Ear squeeze may result in eardrum rupture. When rupture
occurs, this pain will diminish rapidly. If eardrum rupture is suspected, the dive
shall be aborted. Vertigo and/or nausea may occur if water enters the middle ear.
Suspected cases of eardrum rupture shall be referred to medical personnel. Antibi-
otics and pain medication taken orally may be required. Never administer
medications directly into the canal of a ruptured eardrum unless done in direct
consultation with an ear, nose, and throat medical specialist.
Inner Ear Barotrauma.
The round window and oval window are membranes that
separate fluid in the inner ear from the middle ear. Inner ear barotrauma involves
the rupture of one of these membranes and may be associated with the diver who
had difficulty clearing his ears (vigorous Valsalva). However, a rupture may arise
for no apparent reason. Often symptoms of inner ear barotrauma will become
evident on the bottom or after the diver reaches the surface. Symptoms may
include vertigo, hearing loss, or tinnitus. Any hearing loss occurring within 72
hours of a hyperbaric exposure should be evaluated for inner ear barotrauma.
Symptoms of inner ear barotrauma can be confused with symptoms of inner ear
decompression sickness or arterial gas embolism for which recompression therapy
CHAPTER 19 — Diving Disorders Not Requiring Recompression Therapy 19-11
is the only appropriate treatment. Symptoms of inner ear barotrauma will not be
relieved or may worsen with recompression. If there’s a possibility that the symp-
toms of vertigo, deafness or tinnitus may be due to decompression sickness, or if
other neurological symptoms are present, institute recompression therapy. During
decompression from treatment depth, the diver with suspected inner ear
barotrauma should not be exposed to excessive positive or negative pressure when
breathing oxygen on a built-in breathing system (BIBS) mask. The diver should be
kept in an upright sitting position. After surfacing from treatment, bed rest, head
elevation, and hospitalization are indicated until an audiological workup can be
completed by medical specialists.
Middle Ear Oxygen Absorption Syndrome.
Middle ear oxygen absorption syn-
drome refers to the negative pressure that may develop in the middle ear following
a long oxygen dive. Gas with a very high percentage of oxygen enters the middle
ear cavity during an oxygen dive. Following the dive, the oxygen is slowly
absorbed by the tissues of the middle ear. If the eustachian tube does not open
spontaneously, a negative pressure relative to ambient may result in the middle ear
cavity. Symptoms are often noted the morning after a long oxygen dive. Middle
ear oxygen absorption syndrome is difficult to avoid but usually does not pose a
significant problem because symptoms are generally minor and easily eliminated.
There may also be fluid (serous otitis media) present in the middle ear as a result
of the differential pressure.
Symptoms of Middle Ear Oxygen Absorption Syndrome.
The diver may notice
mild discomfort and hearing loss in one or both ears. There may also be a sense of
pressure and a moist, cracking sensation as a result of fluid in the middle ear.
Treating Middle Ear Oxygen Absorption Syndrome.
Equalizing the pressure in
the middle ear using a normal Valsalva maneuver or the divers procedure of
choice, such as swallowing or yawning, will usually relieve the symptoms.
Discomfort and hearing loss resolve quickly, but the middle ear fluid is absorbed
more slowly. If symptoms persist, a Diving Medical Technician or Diving
Medical Officer shall be consulted.
Divers may experience sensations while at depth which they would describe as
dizziness, or in some situations may lose consciousness. The causes of these
conditions are not always obvious and surfacing the diver may not be possible
because of decompression obligations. Therefore, it is important to know what
could cause these disorders in order to decide the possibility of injury to the diver.
The sensation of the diver spinning or the environment spinning is called
vertigo. Vertigo is common and usually transient in divers. There are two types of
vertigo: transient and persistent.
Transient Vertigo.
Transient vertigo typically lasts less than 1 minute. There are
two common forms of transient vertigo: caloric and alternobaric. Caloric vertigo
may be due to unequal cold water stimulation of the ear. This is seen when passing
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through thermoclines, slow clearing of the external ear canals, or eardrum rupture.
Alternobaric vertigo may be caused by pressure differences between the middle
ears on ascent or descent, and typically resolves when the ears are cleared. Travel
should be halted until the vertigo resolves. Once the vertigo resolves, then the dive
may be continued.
Persistent Vertigo.
Persistent vertigo lasts greater than 1 minute. Symptoms may
be caused by inner ear barotrauma, decompression sickness or arterial gas embo-
lism. If persistent vertigo is suspected, abort the dive and consult Diving Medical
Personnel. All cases of persistent vertigo shall be evaluated by a Diving Medical
Unconscious Diver on the Bottom.
An unconscious diver on the bottom is a
serious emergency. Only general guidance can be given here. Management deci-
sions shall be made on site, taking into account all known factors. The advice of a
Diving Medical Officer shall be obtained at the earliest possible moment.
If the diver becomes unconscious on the bottom:
Make sure that the breathing medium is adequate and that the diver is
Check the status of any other divers.
If there is any reason to suspect gas contamination, shift to the standby supply.
Have the dive partner or standby diver ventilate the afflicted diver to remove
accumulated carbon dioxide in the helmet and ensure the correct oxygen
When ventilation is complete, have the dive partner or standby diver ascertain
whether the diver is breathing. In the MK 21, the presence of breath sounds
may be audible over the intercom.
If the diver appears not to be breathing, the dive partner/standby diver shall
attempt to reposition the divers head to open the airway. Airway obstruction
will be the most common reason why an unconscious diver fails to breathe.
Check afflicted diver for signs of consciousness.
If the diver regains consciousness, allow a short period for stabilization
and then abort the dive.
If the diver remains unresponsive but is breathing, have the dive partner or
standby diver move the afflicted diver to the stage. This action need not be
If the diver appears not to be breathing, make further attempts to open the
airway while moving the diver rapidly to the stage.
CHAPTER 19 — Diving Disorders Not Requiring Recompression Therapy 19-13
During recovery of the affected diver:
If conscious, allow a period for stabilization, then begin decompression.
If unconscious, bring the diver to the first decompression stop or the
surface at a rate of 30 fsw/min. Decompress the diver using surface
decompression procedures if required.
If the diver remains unconscious at the first decompression stop and breathing
cannot be detected in spite of repeated attempts to position the head and open
the airway, an extreme emergency exists. One must weigh the risk of cata-
strophic, even fatal, decompression sickness if the diver is brought to the
surface, versus the risk of asphyxiation if the diver remains in the water. If the
affected diver is not breathing, leave the unaffected diver at his first decom-
pression stop to complete decompression and surface the affected diver at 30
fsw/minute, deploying the standby diver as required. Start CPR or Advanced
Cardiac Life Support (ACLS) on the surface if needed. Recompress immedi-
ately and treat accordingly.
Causes and Prevention.
A swimmer or diver can fall victim to drowning because
of overexertion, panic, inability to cope with rough water, exhaustion, or the
effects of cold water or heat loss.
Drowning in Hard-Hat Diving.
Drowning in a hard-hat diving rig is rare. It can
happen if the helmet is not properly secured and comes off, or if the diver is
trapped in a head-down position with a water leak in the helmet. Normally, as long
as the diver is in an upright position and has a supply of air, water can be kept out
of the helmet regardless of the condition of the suit.
Drowning in Lightweight or Scuba Diving.
Divers wearing lightweight or scuba
gear can drown if they lose or ditch their mask or mouthpiece, run out of air, or
inhale even small quantities of water. This could be the direct result of failure of
the air supply, or panic in a hazardous situation. The scuba diver, because of direct
exposure to the environment, can be affected by the same conditions that may
cause a swimmer to drown.
Prevention of Drowning.
Drowning is best prevented by thoroughly training
divers in safe diving practices and carefully selecting diving personnel. A trained
diver should not easily fall victim to drowning. However, overconfidence can give
a feeling of false security that might lead a diver to take dangerous risks.
To treat near drowning:
Assess airway, breathing, and circulation.
Rescue breathing should be started as soon as possible, even before the
victim is removed from the water.
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Give 100 percent oxygen by mask.
Call for assistance from qualified medical personnel and transport as soon as
Thermal stress occurs when the difference between the water and body tempera-
ture 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
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.
Mild to Moderate Hyperthermia.
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 symp-
toms do not improve within 5 minutes, the victim shall be evaluated by Diving
Medical Personnel.
Severe Hyperthermia.
In severe cases of hyperthermia (severe heat exhaustion or
heat stroke), the victim will experience disorientation, tremors, loss of conscious-
ness 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.
Cooling Measures.
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 tempera-
ture. The signs and symptoms of falling core temperature are given in Table 3-1
(Chapter 3). Responses to falling core temperature are individual.
CHAPTER 19 — Diving Disorders Not Requiring Recompression Therapy 19-15
Mild Hypothermia.
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 Hypothermia.
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 rewarmin
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 breathin
Rewarming Techniques.
Remove all wet clothing.
Wrap victim in a blanket (preferably wool).
Place in an area protected from wind.
If possible, place in a warm area (i.e. galley).
Warm shower or bath.
Place in a very warm space (i.e. engine room).
Physiological Effects of Exposure to Cold Water.
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
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.
Laryngeal Stimulation
. Inhaling a small amount of water can induce spasm of
the laryngeal muscles and possibly cause airway obstruction.
19-16 U.S. Navy Diving Manual—Volume 5
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
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 switch-
over, 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
Most physical emergency situations, such as umbilical fouling, entrapment, and
equipment failure, have been mentioned in previous chapters. Those with direct
medical implications will be recounted briefly in this section, with elaboration
when necessary for a clear understanding of the problem and the solution.
Uncontrolled Ascent.
A diver caught in an uncontrolled ascent must exhale
continuously to avoid arterial gas embolism. When ascending, the diver should
vent enough air to prevent the variable volume dry suit from rupturing at the
surface while maintaining positive buoyancy. Treatment of an uncontrolled ascent
is found in paragraph 21-3.6.4 for air diving.
Otitis Externa.
Otitis externa (swimmers ear) is an infection of the ear canal
caused by repeated immersion. The water in which the dive is being performed
does not have to be contaminated with bacteria for otitis externa to occur. The first
symptom of otitis externa is an itching and/or wet feeling in the affected ear. This
feeling will progress to local pain as the external ear canal becomes swollen and
inflamed. Local lymph nodes (glands) may enlarge, making jaw movement
painful. Fever may occur in severe cases. Once otitis externa develops, the diver
should discontinue diving and be examined and treated by Diving Medical
Personnel. Unless preventive measures are taken, this condition is very likely to
occur during diving operations, causing unnecessary discomfort and restriction
from diving.
External Ear Prophylaxis.
External ear prophylaxis, a technique to prevent
swimmers ear, should be done each morning, after each wet dive, and each
CHAPTER 19 — Diving Disorders Not Requiring Recompression Therapy 19-17
evening during diving operations. External ear prophylaxis is accomplished using
a 2 percent acetic acid in aluminum acetate (e.g., Otic Domboro) solution. The
head is tilted to one side and the external ear canal gently filled with the solution,
which must remain in the canal for 5 minutes. The head is then tilted to the other
side, the solution allowed to run out and the procedure repeated for the other ear.
The 5-minute duration shall be timed with a watch. If the solution does not remain
in the ear a full 5 minutes, the effectiveness of the procedure is greatly reduced.
Occluded External Ear Canal.
During prolonged diving operations, the external
ear canal may become occluded with wax (cerumen). When this happens, external
ear prophylaxis is ineffective and the occurrence of otitis externa will become
more likely. The external ear canal can be examined periodically with an otoscope
to detect the presence of ear wax. If the eardrum cannot be seen during examina-
tion, the ear canal should be flushed gently with water, dilute hydrogen peroxide,
or sodium bicarbonate solutions to remove the excess cerumen. Never use swabs
or other instruments to remove cerumen; this is to be done only by trained medical
personnel. Otitis externa is a particular problem in saturation diving if divers do
not adhere to prophylactic measures (see paragraph 15-18.2).
Underwater Trauma.
Underwater trauma is different from trauma that occurs at
the surface because it may be complicated by the loss of the diver’s gas supply and
by the divers decompression obligation. If possible, injured divers should be
surfaced immediately and treated appropriately. If an injured diver is trapped, the
first priority is to ensure sufficient breathing gas is available, then to stabilize the
injury. At that point, a decision must be made as to whether surfacing is possible.
If the decompression obligation is great, the injury will have to be stabilized until
sufficient decompression can be accomplished. If an injured diver must be
surfaced with missed decompression, the diver must be treated as soon as possible,
realizing that the possible injury from decompression sickness may be as severe or
more severe than that from the other injuries.
Injuries Caused by Marine Life.
These types of injuries will depend on the
geographical location and local marine plants and animals. In planning diving
operations, potential marine hazards should be identified and local experts
consulted on treatment experience and antisera availability for treating envenom-
ization. Treatment advice should be formalized into procedures and filed in
Appendix 5C for ready reference during operations. Suitable references on the
subject are listed in Appendix 5C.
Communicable Diseases and Sanitization.
Using unsanitized diving equipment
presents a health hazard that can be avoided easily through proper cleaning proce-
dures. Cleaning and disinfecting procedures vary depending on the equipment and
how it is used. Cleaning instructions for diving equipment are provided in the
appropriate equipment operations and maintenance manual and PMS maintenance
requirement cards.
19-18 U.S. Navy Diving Manual—Volume 5
There are no hard and fast rules for deciding when a medication would preclude a
diver from diving. In general, topical medications, antibiotics, birth control medi-
cation, and decongestants that do not cause drowsiness would not restrict diving.
Diving Medical Personnel should be consulted to determine if any other drugs
would preclude diving.