Signs of Hypoxia Every Diver Should Know

signs of hypoxia every diver should know

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Underwater exploration and deep sea diving can be an invigorating and relaxing activity. However, like all hobbies, diving comes with its own special set of risks and caution. Knowledge of diving goes beyond the simple mechanics of the oxygen tank and wetsuit; divers particularly need to be aware of the potentially deadly signs of hypoxia in themselves and their diving partner. Hypoxia is a unique diving disorder specific to underwater diving. By understanding the principles of hypoxia and learning to recognize the warning signs, divers can protect themselves from deadly or irreversible side effects. Hypoxia is one of the biggest risks of death and injury to divers and can happen within a moment’s notice. Recognizing the signs of hypoxia can prevent serious effects on the body and even death.  

What Is Hypoxia?

In general, hypoxia is the medical term for reduced or insufficient oxygen to the brain. It’s a very dangerous condition and one of the deadliest injuries for divers. In cases where a diver survives hypoxia, he or she will suffer lifelong complications and side effects. A diving death usually follows a series of circumstances or warning signs; recognizing the signs of hypoxia will aid in avoiding an unnecessary injury or death.

Primary Causes of Hypoxia

The brain is in charge of all the voluntary and involuntary actions of your body, from the intentional act of putting on your wetsuit to the unintentional blinking of your eyelids. Without a constant supply of blood and oxygen, the brain will cease to function. Cerebral hypoxia is caused by any situation in which oxygenated blood cannot reach the brain.

There are four primary causes of hypoxia:

  • No blood supply to the brain
  • Low blood supply to the brain
  • No blood oxygen
  • Low blood oxygen

When the blood vessels that supply blood to the brain are blocked or completely obstructed, the brain will suddenly cease receiving oxygen. This is rare but usually fatal with no chance of survival because of the death and breakdown of brain tissue.

In comparison, low blood supply occurs when just one blood vessel is blocked or partially blocked. An example of this would be a stroke; it is common but still causes problematic side effects depending on the length of time the vessel was obstructed. This type of hypoxia can cause damages to specific areas of the brain such as speech or gross motor skills.

No blood oxygen is caused when the body cannot take in oxygen through breathing, or when the heart or lungs cannot provide enough oxygenated blood. Bodily organs begin to shut down due to hypoxia and quickly results in death.

Conditions such as emphysema or a sudden heart attack can cause low blood oxygen. In these situations, the brain – like other organs – is still receiving oxygenated blood but not enough to function properly. Reaction time can slow down and delay both voluntary and involuntary bodily functions.

Hypoxia and Diving

Diving is not a direct cause of hypoxia, but for inexperienced divers, it can be a contributing factor. If you are already in poor health, suffer from a chronic disease, or are at risk for heart attack or stroke, you should not take part in diving. Complications such as asthma can be a dangerous precursor to hypoxia.

Anxiety disorders, panic attacks, and hyperventilation can lead to hypoxia while diving. Inexperience, nervousness, and high stress levels also contribute to the risk of hypoxia. A panic attack will lead to increased and shallow breathing which will not only use up the oxygen reserve but also cause an exertion of energy which uses even more oxygen. Compared to the normal population, experienced divers may go longer periods of time with a lower need for oxygen; but for new and inexperienced divers, oxygen deprivation is dangerous and potentially fatal. However, whether this is your first dive or 100th dive, it is imperative to recognize the signs of hypoxia.

Why Is This Dangerous to Divers?

Irreversible brain damage occurs within a minute or two of oxygen deprivation. After five minutes, severe brain damage and cell death takes place. A relatively healthy person will die from oxygen deprivation within ten minutes; those with pre-existing conditions will die sooner.

Avoiding Hypoxia

Divers are at special risk for hypoxia because of the usage of closed-circuit rebreather systems that control the amount of oxygen in the supplied air. Hypoxia can occur at any time during a dive, from the descent into the waters to the ascent back to the surface. There is a higher risk for divers who are inexperienced, prone to anxiety, or have pre-existing medical conditions such as asthma.

Divers can avoid hypoxia in many ways, including:

  • Enrolling in classes to learn the proper techniques and rules of diving
  • Learning to manage stress or anxiety
  • Increasing depth and dive-time gradually
  • Don’t dive in less-than-ideal conditions
  • Manage ascent properly
  • And most importantly: always dive with a competent buddy and never dive alone


By enrolling in classes, new divers learn the proper rules, techniques, and methods of breathing. The instructor will teach diving students the correct ways to dive and how to use the diving equipment. This leads to more confidence and prevents injuries due to inexperience and stress. Stress and panic attacks can lead to hyperventilation, which is over-breathing. Hyperventilation raises an individual’s heart rate, increases the rate at which a body burns through and uses oxygen, and reduces levels of carbon dioxide in the blood.

Diving Smart

Divers should only embark on a new exploration when conditions are positive. Divers should be well-hydrated and well-rested. Diving while hungry or cold can lead to unnecessary discomfort that causes distractions and lowered mental capabilities. Low blood sugar or irritability can complicate an otherwise easy dive.

Take It Slowly

When you reach the end of your dive and you begin your ascent, it is important to approach it slowly as to not burn through your energy or oxygen. The greatest proportional pressure changes take place within 10 meters below the surface and the volume of air in your lungs increases during this time. Slowing down your ascent slows down the transfer of oxygen from the blood to lungs and conserves your energy. When you stop finning – or, in other words, swimming to the surface – you are not burning through extra energy or oxygen that could otherwise cause a surface blackout.

Take a Friend

The importance of diving with a buddy cannot be overstated. Diving solo versus diving with a friend can be a difference of life or death. When you both recognize the signs of hypoxia, you will know what to watch for to protect each other. If you were to dive alone and blackout due to hypoxia there would be no chance of recovery.

Signs of Hypoxia Every Diver Should Know

Divers must be aware of the signs of hypoxia in themselves and their fellow diving buddy. Diving buddies should never be out of sight from each other and should have an agreement of how often to check each other; for example, some buddies agree to check each other and make eye contact after a certain number of breaths and return OK signs. Always make sure that you and your buddy are on the same wavelength as to OK signs and body language.

Signs of Hypoxia in Self

  • Something blocking your face, mouth, or nose, such as a piece of equipment becoming loose or dislodged
  • Tingling in extremities
  • Gasping for air or not taking slow breaths
  • Loss of consciousness 
  • Disorientation or confusion
  • Hallucinations
  • Tachycardia 
  • Acute, severe headache
  • Coughing 

Signs of Hypoxia in Your Diving Buddy

  • Jerky movements, rapid breathing, or “wide-eyed” look
  • Something blocking the face, mouth, or nose; this can be attributed to the inexperience of diving equipment and failure to check equipment placement prior to the dive
  • Pupils that don’t respond normally
  • Blue or white lips, tongue, or face 
  • Panic or sudden ascent to the surface
  • Coughing or appearance of choking


Hypoxia can cause serious short-term and long-term side effects; in worst-case scenarios, hypoxia results in comas and death. Short-term side effects can include dizziness, concentration and attention problems, and vertigo. Long-term side effects can cause problems with memory, speech, and vision. Nerve cells are particularly sensitive to changes in oxygen and this can cause fine and gross motor problems.  Damage can also occur to the regulation and control hormones in the body, limb weakness, and lack of movement control. The ability to read, write, and comprehend information can also be seriously affected by hypoxia. Irreversible and intense damage can occur upon the onset of hypoxia.  Recognizing the signs of hypoxia in yourself or your diving buddy can potentially save a life. Hypoxia can be prevented through gaining experience diving, maintaining a healthy lifestyle, and always being aware of your surroundings and buddy while diving. The effects of hypoxia cannot be understated and can affect your life and well-being in numerous ways. To an inexperienced diver, there are often no obvious warning signs of hypoxia which increases the risk of death due to panic and hyperventilation. Recognizing the signs of hypoxia and being aware of the signs will enable a diver to feel more confident and safe.    

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