It may seem that drinking and diving go hand-in-hand — after all, what could be better than a few cold beers while relaxing on deck between dives? In truth, it becomes apparent that drinking and diving definitely don’t mix, and the adage “first drink, last dive” exists for a reason. Although many people think of diving as relaxing recreation, scuba can be a deceptively strenuous sport. Often, divers must exert themselves physically underwater, whether swimming against a strong current or completing a long surface swim in rough water. Diving can be mentally demanding, too, as divers must focus on a number of factors simultaneously and be prepared to react quickly and effectively should an emergency arise. Diving can be unpredictable, and small problems can quickly escalate if a diver is not at his best both physically and mentally. Alcohol, even in moderation, can considerably impair our abilities in both respects. We all know that there are health risks associated with the consumption of alcohol even on land; underwater, these same risks are exacerbated and compounded by factors that are unique to diving, such as the effects of nitrogen at depth. Finally, while underwater we are not only responsible for our own safety, but also for our buddy’s. In order to properly fulfill your responsibilities to your diving partner, you must be aware of diving and drinking’s impacts.
Alcohol affects divers most seriously by seriously impairing their judgment and delaying reaction times. These effects, as well as reduced coordination, occur because alcohol depresses the central nervous system, but those who are under the influence are often unaware of these impairments. In a study published in the Journal of Studies on Alcohol and Drugs, conducted by Perrine, Mundt and Weiner, a group of experienced divers were given varying amounts of alcohol and videotaped as they conducted a series of simple pool dives. The scientists rated each diver’s risk of injury depending on his behavior, and afterwards asked each participant to assess their own performance. Those divers who had a significant enough blood alcohol concentration (BAC) to put them at risk of injury were unaware that their performance was any worse than usual, despite it being clear to sober onlookers that they were performing neither normally or safely. The study also found that the tested divers’ performances were significantly impaired even with a BAC as low as 40 mg/dl (0.04 percent). This percentage equates to the consumption of two 12-oz (336 gram) beers in one hour by an adult male of average build on an empty stomach, proving that divers should avoid alcohol entirely before or between dives to maintain performance levels. Dr. Glen Egstrom, a dive- physiology researcher at UCLA, reviewed more than 150 studies exploring the effects of alcohol on performance, and found alcohol to be involved in around 50 percent of all diving accidents that befall people of drinking age.
As well impairing our reaction to situations underwater, drinking alcohol exacerbates a number of other diving-related risks. For example, despite the fact that alcohol is often hailed as having warming properties, the opposite is true. Drinking causes the blood vessels in our skin to expand, which in turn leads to an increased blood flow to the skin, and away from our body’s core. Drinking makes us therefore more susceptible to hypothermia, which is already a consideration for divers since water conducts heat away from the body 25 times faster than air. Alcohol also suppresses shivering, making it more difficult to detect hypothermia in its early stages. Post-dive drinking can also increase the time it takes to regain body warmth after surfacing. Alcohol consumption also affects our blood pressure, as those blood vessels that supply our muscles constrict in response to a heightened blood alcohol level. This is particularly dangerous for divers who are already at risk of heart disease, and could be a contributing factor to diving fatalities that occur as a result of heart attack. The effects of alcohol are compounded when diving because of the way that nitrogen affects our bodies at depth. Nitrogen, like alcohol, is a sedative, which is why the symptoms of nitrogen narcosis so closely resemble those of being drunk. The effects of nitrogen and alcohol are cumulative, meaning that one drink on the surface could have the same effect as two, three, or four drinks depending on the depth of your dive.
The question of whether alcohol affects a diver’s susceptibility to decompression sickness (DCS) has never been conclusively answered. Only a handful of studies have attempted to establish a correlation between alcohol consumption and DCS, and the results have been ambiguous. There is plenty of theoretical evidence, however, to suggest that drinking could increase the likelihood of harmful nitrogen bubbles forming in the bloodstream. The expansion of blood vessels in the skin and the increased blood flow to those areas as a result of alcohol consumption could lead to a faster nitrogen absorption rate than dive tables and computers anticipate. If this is the case, divers could risk contracting DCS even when they adhere to their no-decompression limits. Perhaps the most important way that alcohol could contribute to the risk of DCS, however, is in its capacity as a diuretic. As anyone who has woken up with a hangover headache will know, dehydration is a very real side effect of excessive drinking because we lose more fluid via urination, making our blood thicker as a result. Body tissues then receive a reduced blood flow, impacting their ability to absorb and eliminate nitrogen. Whether or not we feel the effects of drinking the next morning, it has been proven that alcohol can stay in the bloodstream for up to eight hours after consumption. Therefore, even drinking the night before diving could lead to dehydration underwater, and consequently, an increased risk of DCS.
We know that it’s tempting to celebrate an amazing dive with a great night out, especially because most people dive while on vacation. However, the potential consequences of diving and drinking are serious, and sobriety is a small price to pay for safety. It’s a good idea to avoid drinking to excess while on a scuba vacation, or within eight hours of going diving. If you do drink, make sure to hydrate as much as you can before getting in the water even if you feel fine. If you don’t feel your best (either physically or mentally), consider postponing your dives until the next day; the risks of diving while you aren’t on top form are simply too great.