Why Smoking and Diving are Incompatible

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Young woman smoking cigarette

There are many reasons why one ought to quit smoking. But for all you smoking divers, I want to give you even more convincing arguments. None of this is new information.  However, some smokers have either never read it or are in denial.  Incidentally, non-smoking divers who want to skip this might want to reconsider unless your personal policy is not to dive with tobacco users.

So what’s the hype? Smoking is one of the most damaging behaviors and the biggest preventable cause of death in the world.  Here’s the take-home message for divers:

Smoking damages your lungs. Emphysema and tumors are two of smoking’s long-term effects on lungtissue (see Photos 1 and 2).  But smoking even one cigarette causes immediate injury and decreases one’s ability to ventilate (take up oxygen and give up carbon dioxide.)

The respiratory tract is lined with cilia, which look liketiny hairs when viewed under a microscope.  Their function is to clean the respiratory tract by transporting mucous and debris.  Smoking destroys cilia and paves the way for respiratory infections. Not only does smoking decrease ability to clear mucous, but it increases mucous production. Importantly for divers, mucous can block eustachian tubes and prevent equalization. Mucous plugs can trap air in the lungs and set you up for a pneumothorax (a type of lung overinflation injury). Smoking-caused emphysema is another risk factor for developing lung overinflation syndrome as well as arterial gas embolism.

Long-term smoking causes carbon dioxide retention. Smoke-damaged lungs ventilate poorly and unevenly. Some areas of the lung get the blood necessary for gas exchange to take place, but are not being ventilated (don’t “see” gas). In that case, no exchange of oxygen for CO2 occurs. The end result is a person who is hypoxic and retains CO2.[1]

Let’s talk about CO2 production for a minute. Increased aerobic physical activity increases CO2 production, which remains linear to O2 consumption. If we compare identical twins with the same exercise habits and weight, the smoker is generally less fit.  An unfit diver begins producing lactic acid (anaerobic metabolism) more quickly than does a fit diver. Once anaerobic metabolism begins, CO2 production sharply increases as the body buffers the lactic acid produced in an effort to maintain its normal pH. The end product is additional CO2.2

Your CO2 production may even be higher when diving deep because:

  1.  increased gas density causes increased work of breathing, and

  2.  increased ambient pressure causes less efficient gas mixing, resulting in increased dead space ventilation.

Elevated levels of CO2 in diving can kill.  Here’s what increased CO2 does at the surface:

  • Mild elevations may cause headache, confusion, decreased reaction time, and increased respirations.

  • Mild to moderate levels can increase blood pressure, heart rate, and the risk of dysrhythmias.

Levels ≥ 75 mm Hg are associated with profound confusion, somnolence, panic, convulsions, loss of consciousness, and finally death.

Just because you haven’t yet had a problem does not mean you’re safe.  Cave divers who smoke are playing Russian roulette, given that alertness, awareness, and ability to solve problems quickly underwater are absolute requirements on all dives.  Increased workload, long and/or deep diving, and cold exposure stack the odds further.

Smoking and Carbon Monoxide

Another deadly cigarette-generated gas is carbon monoxide (CO). Carbon monoxide competes with O2 for transport sites on the hemoglobin molecule. It binds about 240 times more readily than does O2. If the hemoglobin is studded with CO (carboxyhemoglobin) rather than O2, it cannot oxygenate end organs and ultimately their cells.

So we check and analyze our tanks. We want our tanks filled from reliable sources to avoid contamination. Many cave divers analyze their breathing gas for the presence of CO.  So why would anyone light up before diving, impairing the body’s oxygen-carrying ability?   Heavy smokers have up to 15% of their hemoglobin replaced with carboxyhemoglobin. The half-life of CO is about 4-6 hrs. If you are smoke free for about 12-18 hrs, your CO normalizes but accumulates if you smoke more. Do you really want to waste 15% of your oxygen-carrying capacity before undertaking a cave dive?

Carboxyhemoglobin is even more of a consideration for closed-circuit rebreather (CCR) divers. Open circuit divers exhale the CO that dissociates from hemoglobin.  Divers using CCR simply rebreathe it.

Smoking damages your heart and blood vessels.

Smoking constricts blood vessels.  Over the long term, plaque forms inside the blood vessels.  More immediately, nicotine causes chemically mediated vasoconstriction that results in increased blood pressure.  The end result is insufficient blood flow to vital organs. This is particularly harmful during increased physical activity, which diving typically demands. If the heart does not get enough oxygen, it starts to die.  Most people experience chest pain and seek treatment, but some die suddenly due to dysrhythmias.

Constricted blood vessels also inhibit off gassing, theoretically making you more susceptible to decompression Illness (DCI). Most cave divers are careful about dive and decompression planning, but ironically some ignore the obvious danger of lighting up.

Smoking is associated with more severe DCI symptoms

A 2003 study2 linked heavily smoking divers to more severe DCI symptoms (compared to lighter smokers who developed less severe symptoms).  This study did not prove that smoking causes DCI. But it demonstrated that smokers suffered more severe symptoms than did non-smokers.

The more seriously you dive, the more fit you need to be.  Cave diving is serious business.  Ignoring its fitness requirements increases your risk of a bad outcome in addition to the risks inherent in the dive itself.  For all the logistical and gas planning cave diving requires, all of the contingency plans and redundant equipment, continuing to smoke just does not make sense. If you don’t want to quit smoking, you might want to consider quitting diving.

Strategies for Quitting

Some people can quit more easily than others.  Make the decision and stick with it.  Hopefully your passion for diving and your desire to take it further is more than enough to get you through the hard part. Generally, the “hard part” lasts for the first two weeks. It takes time for the nicotine (which causes the physical craving) to disappear, and then you need to reset your psyche to stop craving it out of habit.

Quitting cold turkey may be more successful because your will power is the strongest then. Weaning off may work to decrease your overall nicotine load and craving. But don’t kid yourself. Weaning yourself by one less cigarette per week is meaningless. And while weaning, you need to keep your end goal firmly in mind.

While quitting, avoid smokers.  Even smelling smoke on someone’s clothing may make you want to light up again.

Don’t go out drinking with your buddies for the first three weeks or longer. Alcohol will lower your will power and before you know it, you light up again!

Even if you relapse, get off it ASAP and continue with being smoke free.

Using a patch or gum or other nicotine containing compounds may help reduce the craving, but eventually you’ll need to get off this, too. Nicotine is bad news. It hardens your arteries and decreases blood flow throughout your entire body. Using it is not compatible with doing any serious diving.  (This goes for snuff and chewing tobacco, as well).

To divers who are battling to stop, you have my sincerest best wishes for success. If you still smoke and have not made the decision to stop, I hope that my arguments will give you the insight from which determination is born to help you decide to quit.

Claudia L Roussos MD

Diplomate, American Board of Anesthesiology

Add Helium Dive Team

As published in Underwater Speleology, Volume 39, Number 4, October/November/December 2012, 16-17

  1. There is an interesting write-up on CO2 retainers and the Navy. Check out this link:

  2. The hydrogen atom (H+) on the Lactic Acid combines as follows to ultimately increase water and CO2: 2H+ plus HCO3- equals H2CO3 equals H2O plus CO2

  3. “Effect of Cigarette Smoking on the Severity of Decompression Illness (DCI) Symptoms” by Buch, DA; Dovenbarger, JA; Uguccioni, DM; El-Moalem, H; Moon, RE Aviat Space Environ Med. 2003 Dec; 74(12): 1271-4