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Diving Emergencies


Scuba diving encompasses a wide range of interests and a variety of participants, including recreational divers who enjoy touring the reefs and looking at marine life, commercial divers who work in underwater construction, and public safety divers who perform search and rescue operations.

Whatever the reason for diving, all divers are subject to a special set of environmental and physiological factors. Diving emergencies present unique issues for EMS providers, so having a general understanding of concepts related to diving will be valuable in the event you ever need to respond to the scene of a diving emergency.

Overview of Gas Laws

Before discussing diving emergencies, let's look at how certain gas laws relate to diving emergencies.1 There is no need to memorize the laws, but being familiar with the general principles provides a background for later discussion.

Boyle’s Law states that gas volume is inversely proportional to pressure. A familiar example can be found in the release of a balloon into the air. As the balloon ascends, the pressure on the outside of the balloon is reduced, the air inside it expands and the balloon will eventually burst. If the balloon is taken underwater, it will get smaller. Boyle’s Law also explains why you may feel pain in your ears during take-off and landing when flying. A diver is subject to this same compression and expansion of air, which can lead to barotraumas or pressure injuries.

Dalton’s Law provides that each gas in a gas mixture contributes a portion of the total pressure exerted by the entire gas mixture. Reducing pressure basically makes air “thinner.” For example, the air pressure in Denver is lower than in New York, which is part of the reason why New York athletes may have trouble catching their breath in Denver.

Henry’s Law provides that increased pressure on a gas will force gas into a liquid; decreased pressure will cause gas to be released from a liquid. When you open a soda, the pressure on the soda is reduced and results in “fizzing” as bubbles are released from the liquid. Similarly, gas forced into and released from tissue while diving forms the basis of decompression sickness or “the bends.”

Diving Emergencies

Start of the Dive

When a diver enters the water, his body responds to the change in temperature, including a reduction of peripheral blood flow to maintain core temperature. The reaction may also include a gasp for breath, which could, in extremely cold water, escalate into hyperventilation and drowning. Immersion can cause arrhythmias leading to syncope or death. Death is rare from the initial immersion, but if an emergency developed at the beginning of a dive, a reaction to initial immersion should be kept in mind.2

General Environmental Considerations: Hypothermia, Hyperthermia & Dehydration

Although divers take steps to keep warm while diving, heat loss will occur. Divers on vacation often make multiple dives per day and subject themselves to prolonged cooling over the course of the day. Further heat loss (and gain) can occur as divers are exposed to the sun or wind between dives.3

Diving also causes “immersion diuresis,” which can lead to dehydration and associated issues, including syncope and arrhythmias.4  Dehydration is exacerbated by other factors, including carrying equipment, exposure to sun, breathing dry, compressed air, airplane travel and taking diuretic medications.

Hypothermia, hyperthermia and dehydration should be treated in accordance with your local protocols. Keep in mind that certain signs and symptoms of these conditions, such as nausea, are also associated with other diving injuries.


In much the same way you may feel ear pain during take-off or landing during a flight due to pressure changes, the changes in pressure when diving can cause injury to ears, sinuses and other air spaces. Although decompression illness and other emergencies are dramatic, ear injuries are much more common.

Ears & Sinuses

Divers are trained to equalize the pressure in their ears to ensure that air enters the middle ear through the eustachian tubes.5 Pressure may be felt quickly, and a 10- to 12-inch descent can be sufficient to cause discomfort and pain. Barotitis media (middle ear barotrauma) occurs when pressure in the middle ear is lower than the surrounding pressure (which may occur during descent), forcing the eardrum inward and causing pain and bleeding. A pressure differential can also cause the eardrum to tear or rupture, which results in pain and bleeding. Water entering the ear may cause vertigo, which is very dangerous when it occurs at depth.6 The membranes in the sinuses can also be damaged by pressure. Note that sinus barotrauma and related injuries can occur both during descent and ascent. When ascending, the mechanism of injury is reversed as air expands.

An injury to the ears will manifest as a feeling of fullness, pressure or pain. There may also be a hearing loss or complaints of a “squeaking sound.” Blood or other fluid discharge from the ear may be evident. A sinus injury can also cause fullness, pressure or pain (including pain in the upper teeth) with blood or other discharge from the nose.

Divers with suspected barotrauma should not return to the water. They need to be assessed by a physician for proper treatment, which may include antibiotics, antihistamines and surgery.

Effects on the Lungs

 The effects of the change in air volume and the other gas laws form the basis of decompression illness (DCI), which includes arterial gas embolism (AGE), and decompression sickness (DCS), commonly known as “the bends.”

If a diver takes a breath of air and starts to ascend while holding his breath (or with air otherwise trapped in the lungs), the air expands as the ambient water pressure decreases, much like air expanding in a balloon. This can damage the alveoli and bronchial passages.

Expanding air may rupture the lung and cause a pneumothorax. Mediastinal and subcutaneous emphysema can result from air that escapes from the lun. AGE occurs when bubbles are forced into the bloodstream through alveoli, resulting in blockages when the bubbles reach smaller blood vessels. A cerebral arterial gas embolism (CAGE) results if the air embolizes in the brain.

AGE will usually occur either during a dive or within 15 minutes after a diver surfaces.7 Symptoms include chest pain, coughing and shortness of breath, bloody or frothy sputum, headaches and/or dizziness, visual disturbances (including partial or full blindness), numbness and/or tingling, weakness or paralysis and loss of sensation in the body, and syncope.

DCS: “The Bends”

As a diver descends, the increased ambient pressure forces inspired nitrogen into tissue.8 When a diver ascends the pressure is reduced and nitrogen is released from tissue into the bloodstream. If a diver ascends too quickly, has been down too long or otherwise has excessive amounts of nitrogen in his body, bubbles may form in the bloodstream or remain trapped in tissue.9

Since bubble formation can occur in any tissue, there are many forms of DCS. Pain may occur in the limbs or joints. Central nervous system DCS can cause paralysis and loss of sensation. Cerebral DCS may produce headaches, visual disturbances, paralysis, unconsciousness and altered mental status. “Skin bends,” or cutaneous DCS, present with itching, burning or mottling of the skin.

The onset time of DCS varies within 24 hours of diving. In a recent report, half of all cases of DCS had symptom onset times of an hour and a half or less after a diver surfaced. Any symptoms that occur after 24 hours are probably unrelated to diving. In rare cases, divers exposed to altitude may exhibit initial symptom onset after 24 hours.

DCI Treatment

The treatment for suspected cases of any DCI, including AGE and DCS, are essentially the same, with the ABCs as a priority. The importance of administering 100% oxygen cannot be over-emphasized in suspected cases of DCI. In addition to providing respiratory support as it does in any emergency, oxygen promotes the elimination of inert gas bubbles in the tissues. Dive boats often have oxygen on hand, and someone may have begun administering oxygen prior to EMS’s arrival. DCI can be life-threatening, and any suspected DCI requires immediate transport to a medical facility where a complete diagnosis and treatment, such as hyperbaric chamber therapy, can be done. Note that changes in altitude can exacerbate a case of DCI, so if the patient needs to be transported by helicopter, it should be at the lowest safe altitude possible. The current recommendation is 1,000’ or lower .  A physical exam, including a thorough neurological examination, should be performed and changes should be monitored carefully. Never attempt “recompression” by placing a diver back into the water.

Breathing Dangers      

Nitrogen Narcosis

Inert gases under pressure have an intoxicating effect. Nitrogen under pressure can cause nitrogen narcosis, which impairs the ability to think and reason. Divers can usually stop nitrogen narcosis by ascending until symptoms resolve. The danger of nitrogen narcosis lies in impaired judgment, causing divers to lose track of time, remaining air and depth limits and resulting in agitation, panic or confusion. This can lead to various problems, including drowning when they run out of air, or increasing the chances for serious injury or illness by ascending too rapidly.10

Oxygen Toxicity

Divers run little risk of oxygen toxicity when they stay within recreational depth limits of 130’ and use dive regular air, but it becomes a concern when they use mixed gases like enriched air nitrox.11 There are two types of oxygen toxicity. The first is central nervous system (CNS) oxygen toxicity. Signs and symptoms of CNS oxygen toxicity include convulsion, visual disturbance, tinnitus, nausea, tingling, twitching, muscle spasms (especially along lips and mouth), irritability, dizziness and/or dyspnea. CNS toxicity is the more dangerous form of oxygen toxicity due to the risk of having convulsions under water.

The second type is pulmonary toxicity, which can affect the lungs or other parts of the body. Symptoms include chest pain and discomfort, coughing and fluid in the lungs.

Carbon Monoxide Poisoning

Carbon monoxide poisoning can occur when the air in a scuba tank has been contaminated by fumes from an improperly maintained air compressor. Carbon monoxide poisoning often produces no symptoms before the diver loses consciousness, although there may be symptoms including headache, dizziness, nausea or altered mental status. There may also be excessive red or blue coloring of the lips, nail beds or skin. Patients with suspected carbon monoxide poisoning should be given oxygen.

Asking Questions On Scene

As in any other emergency, fact-gathering is important. Divers are trained to dive in a way that reduces the chance of DCI or other injury, but they may still experience problems even if they follow all the rules. In addition to medical history and other information you normally gather, there is information particular to diving that treating physicians will find useful.

Questions that need to be asked include:

  • “How long did it take the diver to ascend to the surface, and did he stop along the way?” A slower controlled ascent coupled with one or more stops helps the body off gas before bubbles form and also helps prevent barotraumas from air expansion.
  • “How deep and long was the dive?” There are recommendations on how long a diver may remain at various depths in order to minimize the risk of bubble formation.
  • “How long was it before the diver showed signs or symptoms?” DCI (including different forms of DCS) will present at various times based on severity and the type of DCI.
  • “What type of breathing gas was the diver using?” The gas mixture can help determine what illness or injury occurred. Divers are normally trained to dive with a buddy, who may be able to provide information.

Don’t interfere with the equipment the diver was using other than to close the valves on the tank and note the number of turns it took to close the valve.12 There may be regional differences regarding what actions should be taken, including whether you should close the valves on a tank, so follow local procedures and defer to the judgment of law enforcement or other investigators on scene.

Is There A Diving Emergency?

As mentioned, many cases of DCI and other emergencies will present quickly, but others will have delayed signs and symptoms. For example, air travel after diving can cause or exacerbate DCS. Though recommendations vary, based on different factors, a general rule is that divers should not fly within 24 hours after their last dive. If questions you ask a patient reveal recent air travel or diving activities that lead you to suspect a diving injury or illness, it should be treated accordingly.

Case Studies

Patient #1: You are called for a 45-year-old woman who passed out at a restaurant in the early evening. Upon your arrival, she is sitting up and conscious. Her friend tells you they have been diving the last few days from a small uncovered boat and have ignored the crew’s offers of drinking water to avoid having to urinate during the day. The friend says they came out for some food and drinks, as evidenced by a half-empty wine bottle. The medical history reveals that the patient has never had a syncopal episode before, but she has a history of hypertension and has been prescribed medication that you know has a diuretic effect. The combination of sun exposure, immersion diuresis, medication, refusal to drink water and consuming alcohol has caused dehydration that resulted in syncope. The patient should be assessed by a physician to rule out any other potential causes of syncope.

Patient #2: You are called to the hotel room of a 30-year-old male with no medical history, who began experiencing some minor pain in his shoulders and tingling in his arms 20 minutes earlier. The pain has increased “from 2 to about a 4” on a 1-10 scale. He tells you he has been diving the last few days “pretty deep and for good long dives,” but says he thought he was close to, but did not exceed, the maximum recommended guidelines. He completed multiple dives over the last few days; his last dive was completed 8 hours ago. You place him on oxygen, and your exam during transport does not reveal any neurological deficits. Even though he did not exceed any recommended guidelines, it does not mean he is 100% “safe” from having DCI, especially since he did many deep dives over a few days. Treatment in a hyperbaric chamber often resolves all symptoms.

Patient #3: A call comes in from a local pier where a boat is arriving with a 50-year-old male diver who is having trouble breathing. The boat is docking when you arrive, and you see a diver on the deck wearing a blood-spattered oxygen mask. His wife, who was diving with him, says they were fairly deep and had began ascending to end the dive when she noticed her husband had not ascended and was many feet below her staring into the water. She banged on her tank to attract his attention and headed toward him, but, before she could reach him, he looked at his air gauge and headed “like a rocket” to the surface. Immediately after surfacing he began complaining of pain in his chest and difficulty breathing. The crew placed him on oxygen and, within minutes, he began coughing up blood. The rapid ascent and quick onset of signs and symptoms indicates that this may be a case of pulmonary barotrauma. His confused behavior during the dive indicates he may have been experiencing nitrogen narcosis, which ultimately leads to a rapid and dangerous ascent. He should be provided oxygen and transported immediately.

Stings and Envenomation

Fish, corals and other marine life have developed offensive and defensive mechanisms that can produce injury and death. Swimmers, snorkelers, divers and general beach-goers are all subject to these hazards.


Jellyfish generally refers to certain marine animals that inflict venom through stinging cells called nematocysts. The term includes Portuguese man-of-war, fire coral, anemones and box jellyfish/sea wasps. Jellyfish stings usually result in skin reactions, including burning and redness, though more severe reactions like anaphylaxis and respiratory paralysis can occur. In the event of a jellyfish sting, attend first to ABCs, then dislodge the tentacles by rinsing them with vinegar or salt water. Fresh water should not be used since it can cause the remaining nematocysts to “fire.” The venom will break down with heat, and immersion in hot water (113°F/45°C) for 30 to 90 minutes will neutralize remaining nematocysts. Hot packs may also be used to control the pain.

Do not touch any marine animal or any patient without putting on gloves. Nematocysts can still fire from dead marine life washed up on the beach.


Stingrays are generally docile creatures, but are equipped with a tail that has sharp barbs used for defense, most often on an unsuspecting person who has the misfortune to step on it. The tail inflicts a deep puncture and/or laceration together with an envenomation. The pain is often severe and accompanied by bleeding. Reactions include weakness, fainting and, in more extreme cases, anaphylaxis, paralysis and death. You should first establish ABCs, then rinse the wound with clean water and immerse in hot water (110°F-113°F/43.3°C-45°C) for 30 to 90 minutes. Extract obvious pieces of barbs, then conduct pain management as needed.13  As with any wound, there is a risk of infection from the puncture.

Experts a Phone Call Away

A valuable resource in the event you ever encounter a diving emergency and need assistance is the Divers Alert Network, or DAN ( DAN is available 24/7/365 to answer dive emergency questions and offer assistance during diving emergencies.  DAN can also direct you to the nearest emergency care facility with staff trained in diving medicine.  DAN’s dive emergency telephone number is 919/684-9111. 


 This article is a general overview designed to remove some of the mystery surrounding diving emergencies. There is a wealth of material available for review that goes into further details of the “hows and whys” of diving medicine and emergencies, ranging from the theories of bubble formation to whether certain conditions like diabetes or spontaneous pneumothorax are contraindications to diving.14 DAN’s website and the books referenced in the endnotes are highly recommended if you would like to pursue the subject further.

1. Note that the effects of the gas laws are not totally distinct, and one or more may contribute to various illness and injury.
2. Chapter 2, p. 37. Diving Physiology In Plain English (“Diving Physiology”). Ed. Jolie Bookspan. Undersea and Hyperbaric Medical Society, 5th printing (2003). Also see Diving and Subaquatic Medicine, 4th Edition, p. 295, 2005.
3. Conditions for hypothermia, hyperthermia and dehydration can exist at the same time. For instance, divers can “gear up” with heavy equipment in the heat of summer and be subjected to extreme cold when they enter the water.
4. Diving Physiology, Chapter 2, p. 43, 2003.
5. Divers use a variety of techniques to ensure that the air pressure in spaces, particularly the ears, is the same as external pressure. These techniques include yawning, swallowing or pinching the nostrils and blowing air through the eustachian tubes using a Valsalva maneuver. Equipment like masks also have air spaces that divers equalize. Any place where air can be trapped, including improperly filled cavities in teeth, are subject to barotrauma.
6. Vertigo can escalate into other problems as the diver becomes confused, disoriented and/or panics.
7. Diver’s Alert Network, Annual Diving Report, p. 34, 2008. The presence of neurological symptoms and an onset time of 15 minutes or less is generally used by DAN to determine a “probable” case of AGE.
8. Different tissues absorb gas at different rates. Some tissue may be saturated, while other tissue is still absorbing nitrogen. Bubble formation is an extensive subject area, and the example is general.
9. Divers use various tables and computers in order to reduce risks associated with bubble formation. Recreational divers generally do no-decompression dives so they can descend and ascend without having to stop and allow additional time for nitrogen to be removed. As a matter of caution, no-decompression dives may include a “safety stop” at 15 feet for 3-5 minutes. A decompression dive requires one or more stops while ascending.
10. Drowning is always a concern when responding to a diving emergency and is the most common cause of scuba-related death. Over 50% of recreational scuba-related deaths among recreational divers were due to drowning. Divers Alert Network, Annual Diving Report, p. 59, 2007 edition, Durham, NC. It should be noted that drowning is often listed when other causes of death could be involved, since drowning will ultimately occur.
11. Nitrox refers to a gas that contains oxygen and nitrogen where the percentage of O2 is higher than 21% as found in normal air.
12. Diving Physiology, p. 511, 2003.
13. Keep in mind that the barbs are a penetrating injury, and you should defer to standard protocols or consult medical control.
14. Divers with diabetes can dive, and there are recommended guidelines on monitoring blood sugar before and after the dive. A history of spontaneous pneumothorax is a generally considered to be a contraindication to diving.



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