15 Worst-Case Scenarios for Scuba Divers

Most divers are cautious and attentive in the way they prepare for and conduct themselves while diving. They know the rules and limits, they check their equipment over carefully, and they don't push the limits too far or too often. When it comes to injuries, we're probably more likely to get hurt playing softball or soccer than we are to suffer an injury on a dive. But when that unusual circumstance comes along, it's important to have a plan. After all, we can't stay underwater forever, and some problems need to be resolved pronto. We need to think about what could possibly go wrong on a dive, and have a plan for what to do if that “worst-case scenario” should arise.

With that in mind, we'll take a look at some of the most challenging situations a diver can encounter. For each one, we define the scenario, identify the risk factors, examine the likely causes and suggest strategies for avoidance. Then we'll explore the various tactics to deal with the problem just in case it sneaks up on us.

Scene from the movie Open Water

Stuck Autoinflator Valve

Pausing to make that minor adjustment to your buoyancy, you gently press the autoinflate button of your buoyancy compensator (BC). Instead of adding just a “puff” of air, the valve jams and begins to empty the contents of your cylinder into your BC. It's think fast, or face an uncontrolled ascent.

Risk Factor: Rapid or uncontrolled ascent, with attendant risk of pressure-related injuries.

Likely Causes: Probably the most common cause of a stuck BC inflator valve is poor or neglected maintenance. Some divers just don't give their BC the post-dive attention it deserves. If a BC is not rinsed or soaked after diving in salt water, salt crystals and mineral deposits can form that can later cause the valve to stick in the “on” position. Another potential cause of a stuck BC inflator valve is sand, silt or other sediment in the valve mechanism. This can occur if the device isn't properly secured and drags on the bottom.

Avoidance: Proper care of your BC goes a long way toward preventing stuck inflator valves. After each dive, or each day of diving, thoroughly rinse and/or soak the BC in fresh water to dissolve any salt crystals and to remove sand, silt and other debris.

Dealing With It: The fastest way to solve the problem of a stuck inflator valve is to disconnect the low-pressure hose from the inflator. Failing that, grab the lanyard for the dump valve and hold it open. Should an unwanted ascent begin, continue venting the device, and flare your body to maximize drag and slow your ascent.

Grabbing hold of a stationary object such as an anchor line might allow you to sort the problem out and regain buoyancy control.

BC Won't Inflate

While making a descent you realize you're a wee bit heavy, so you try adding air to your BC. Nothing happens, and instead you get that sinking feeling as you begin to accelerate toward the deep blue beyond.

Risk Factor: Loss of buoyancy control, uncontrolled descent, with attendant risk of exceeding depth limits.

Likely Causes: Several problems can result when an autoinflator fails to inflate a BC. The first and most obvious is that you forgot to attach the low-pressure hose to the inflator. The second is that you ran out of air, but we'll discuss this later. A third possibility is a mechanical malfunction or failure of the inflator valve.

Avoidance: Carefully check your dive gear prior to entering the water to verify that the low-pressure hose is connected to the inflator, and then verify that the device actually works. Recheck it once you're in the water to make certain the hose wasn't disconnected by the force of entering the water. To avoid mechanical problems with the valve, thoroughly rinse your BC after diving, and take it to your local dive center for professional maintenance at least yearly.

Dealing With It:
If the low-pressure hose is disconnected, reconnect it and your problem should be resolved. Plan “B” is to use the oral inflator to add air to your BC. (This is a skill that should be practiced.) Finally, if you've got that sinking feeling and can't correct the problem quickly enough, ditch enough weight to establish neutral buoyancy.

Regulator Freeflow

Everything is going fine when suddenly your regulator erupts, spewing out the contents of your cylinder.

Risk Factor: Difficulty breathing, rapid exhaustion of breathing air supply.

Likely Causes: Regulator problems such as freeflow generally stem from poor regulator maintenance and are made worse by moisture in the cylinder and cold-water temperatures. As compressed air expands in the regulator, the temperature drops, which can cause moisture in the air to freeze. This in turn can unseat a valve. As regulators get cold from air expansion, ice can form on exterior components as well. Incorrectly set interstage pressure can also make a regulator prone to freeflow.

Avoidance: Proper maintenance is critical to regulator reliability. Regulators should be properly rinsed/soaked, to prevent the buildup of salt and mineral deposits that can foul up the valves. Rinse or soak your regulator after each dive, and have it serviced by a professional technician annually Before diving in cold water, make certain that the regulator has been serviced for cold water, and that the cylinder has been properly serviced and filled.

Dealing With It: While it is often possible to continue breathing from a free-flowing regulator, some divers will experience difficulty due to the torrent of bubbles. If breathing from the free-flowing regulator is not possible, switch to a redundant air source or share air with a buddy. Shut off the cylinder valve to conserve air and stop the bubbling, and make a controlled, normal ascent to the surface. You may need to orally inflate your BC if the cylinder air has been turned off.

Computer Failure

You look down to check your depth and dive time, and your computer's screen is blank, frozen or otherwise unreadable.

Risk Factor: Computer failures come in a variety of forms, but the net effect is usually a loss of critical dive information. A diver who suffers a dive computer failure is at risk of exceeding depth and/or no-decompression limits, or running low or out of breathing gas (lacking or inaccurate cylinder pressure data).

Likely Causes: Computer failures are rare, but they can occur. Although regular servicing is important to reliable operation, it is no guarantee against failures. Loss of battery power during a dive is one of the more commonly reported problems with dive computers.

Avoidance: Step one is to have fresh or freshly charged batteries before each dive. Beyond that, divers can be ready to deal with computer malfunctions by carrying either a backup dive computer, or backup timer and depth gauge. For those with integrated air computers, a backup cylinder pressure gauge is also in order.

Dealing With It: When a dive computer problem occurs, the general rule is to terminate the dive, unless you have a personal backup that allows you to continue safely. Don't rely on another diver's dive computer except as a means of monitoring your ascent rate. Remember too that switching to a new or “fresh” computer doesn't necessarily solve the problem unless the new computer can be programmed with any dive profiles you've completed in the past 24 hours.

Accidental Weight Loss

You're roaming the reef, minding your own business, when you become buoyant.

Risk Factor: Most people welcome unexpected weight loss, but not when diving. Whether it's a loss of a weight belt, trim weight or individual weights from a pocket belt or integrated weight system, losing weight generally leads to an uncontrolled ascent, possibly of the rapid nature. This can lead to lung over-expansion injuries such as arterial gas embolism (AGE) and can contribute to decompression sickness.

Likely Causes: Loss of weights when diving can be the result of poor or neglected maintenance, mechanical failure or poor operating procedures.

Avoidance: A thorough inspection of your weight system prior to diving is the first step in avoiding accidental weight loss. Look for telltale signs such as worn Velcro fasteners and stitching, worn buckle teeth, and faulty release mechanisms. When using a conventional weight belt, make certain that the strap length is appropriate. There should be 4-6 inches of extra strap remaining when the buckle is secured. Less than that, and there may not be enough to grip to make underwater adjustments. Too much excess strap can lead to entanglements. During the dive, monitor your weight system, and adjust the belt tension as necessary.

Dealing With It: The first step in dealing with an accidental weight loss is to counter the effect by dumping air from your BC. If you're at the bottom and can find something to hang onto, it may be possible to retrieve and replace the lost weight and continue the dive. If an uncontrolled ascent begins, flare your body to maximize drag and slow your ascent, vent air from your BC and remember to exhale during the ascent.

Out of Air

Everything is going swimmingly, and then you start to take a breath, and nothing!

Risk Factor: The most obvious risk factor for an out-of-air scenario is the inability to breathe — a situation that must be resolved right away. Panic and rapid ascents can result in decompression illness and pressure-related injuries.

Likely Causes: Out-of-air scenarios are usually the result of poor air management techniques, distraction or mechanical failures. When divers aren't in the routine of checking air supply or become engrossed in other aspects of the dive, time (and air supply) can pass quickly, and the onset of a low-air situation may occur unnoticed. Failure to carry secondary air supply and drifting too far from a buddy can complicate the scenario by removing the best emergency options from the table.

Avoidance: As part of the process of avoiding worst-case scenarios in diving, make monitoring your air supply a normal part of your routine. Plan your dive to ensure a supply of reserve air suitable for the particular environment and situation. Make certain your dive equipment receives a thorough pre-dive inspection, post-dive cleaning and periodic professional maintenance. Be properly equipped with an alternate/redundant air supply, and follow established buddy procedures to ensure you're never “alone” underwater. If your diving style could leave you separated from your buddy, consider a redundant air supply rather than relying on your primary air cylinder as a backup.

Dealing With It: While running out of air is definitely a stress-inducing scenario, it shouldn't cause panic. The first thing to do is switch to an alternate air supply — either yours or your buddy's. If your buddy isn't at hand and your cylinder is “empty,” begin a controlled ascent to the surface, remembering to exhale as you go. Activate an audible signal (e.g., bang on your tank with a knife) to bring your situation to the attention of other nearby divers. As the ambient pressure decreases, more air may be available from the “empty” cylinder.

Wet-Breathing Regulator

Rather than the usual dry air, you find that each breath brings with it a spray of water. Hmmm, that's not right!

Risk Factor: Water entrained in the breathing air can make it difficult to breathe, or may cause coughing and choking. This can lead to stress, panic and an uncontrolled ascent.

Likely Causes: Several problems can cause wet breathing. A split or torn second-stage diaphragm or mouthpiece can allow water to be drawn into the airstream, causing wet breathing. A loose or damaged mouthpiece can also translate to wet breathing.

Avoidance: Proper inspection and maintenance of your dive gear is critical to avoiding the wet-breathing scenario. As part of your predive equipment inspection, take a breath from your regulator with the air turned off. If you can draw even a small amount of air, there is probably a hole or split in the diaphragm, which should be replaced before diving. Verify that your regulator mouthpiece is in good condition, and is securely attached to the second stage. Most are secured with a nylon cable tie. Replace worn mouthpieces and missing cable ties.

Dealing With It: A wet-breathing regulator should be considered more of a nuisance than a true emergency. If you do experience wet breathing, try inhaling more slowly or gently to minimize the internal pressure drop and reduce the entrainment of water. Terminate the dive and have the problem regulator serviced.

Separated Mouthpiece

You turn your head to look at a passing angelfish, and suddenly you're sucking a slug of water. What the… ?

Risk Factor: The risk factors for a separated mouthpiece scenario include inhalation of water, choking and the inability to breathe. Any of these can cause stress and lead to panic, rapid ascents, decompression illness and pressure-related injuries.

Likely Causes: The problem of a separated mouthpiece comes as the result of neglected maintenance and a poor pre-dive equipment check. A missing fastener or failure of the mouthpiece material can cause the mouthpiece to separate from the regulator.

Avoidance: The best way to prevent a separated mouthpiece is to inspect your regulator carefully and thoroughly before every dive, and replace worn mouthpieces and missing ties.

Dealing With It: The best way to deal with a separated mouthpiece is to immediately switch to your safe second. If your lungs are empty and you can't purge the regulator by exhaling, use the purge button. If switching to your alternate air means you no longer have a backup regulator, terminate the dive.

Blown Deco Stop

You get to the surface after a dive, and then realize that you were supposed to stop to decompress. Drats! What to do next?

Risk Factor: Missing a required decompression stop puts you at significant risk of DCI.

Likely Causes: Blown deco stops sometimes occur when a diver becomes distracted, or suffers from an equipment problem or failure that requires or leads to an immediate ascent to the surface. They can also be caused by problems such as entanglements that occur as a diver nears the end of the dive, and as air supplies run low.

Avoidance: Several strategies can be used to help avoid blown deco stops. First and foremost, be sure to monitor your dive carefully. Consider the environment carefully, and plan your dive so that you have plenty of reserve air and time to deal with problems that can crop up at the end of the dive. Finally, give your equipment a thorough pre-dive check to ensure there are no maintenance “loose ends” that could cause the dive to “come undone.”

Dealing With It: The general rule for missing a required decompression stop is to begin the use of breathing oxygen and seek medical attention. Avoid the temptation to simply switch gear and return underwater to complete the missing deco stop, as further medical complications can develop that could require the assistance of personnel on the surface.

Can't Find the Dive Boat

You surface after a dive expecting to board the boat, but wait a minute! Where is it?

Risk Factor: Among the risks inherent in being separated from the dive boat are those of being left behind, exposure and dehydration.

Likely Causes: Among the reasons that divers find themselves separated from the dive boat are navigational problems, poor visibility, currents, distractions and separation from a buddy or dive group.

Avoidance: Among the keys to avoiding the problem of being left behind are careful predive planning and solid underwater navigational skills. In addition, divers should carry a variety of surface signaling devices and tools to draw attention to their location in the event that they do become separated from the boat. Such equipment should include as a minimum a surface marker buoy (SMB) or “safety sausage,” signaling mirror, whistle or air horn, a dive light and strobe. Yet another strategy to avoid being left behind is to make certain that another buddy pair will check for you before the boat leaves the dive site. Also, make certain that someone on shore knows where you are going (name of the boat), when you should return, and whom to contact in the event that you don't return as scheduled.

Dealing With It: If you do become separated from the dive boat and are left behind, use every means available to signal other boats or passing aircraft. If you're near shore, you may improve your chances of survival by getting to land. Otherwise, stay cool and wait it out until help arrives.

Unfamiliar Buddy

At the last minute, your buddy decides not to make the dive, and you're stuck diving with a stranger.

Risk Factor: Any time we dive with an unfamiliar buddy, we run the risk of not working well together as a team. Especially if an abnormal situation develops, unfamiliar buddies may be less likely to resolve the situation effectively and safely as compared with dive buddies who dive together regularly.

Likely Causes: Despite the commonalities among different certification agencies and instructors, not all divers follow the same buddy procedures or communication protocols. Divers vary in how close they stay to one another, the roles they assume in the buddy system and how frequently they communicate with one another during a dive. And that's just for starters. Teaming with an unfamiliar diver not only requires a sorting out of these basic buddy issues, but also demands familiarization with each other's equipment.

Avoidance: When possible, dive with a familiar buddy, but if that isn't possible, take the steps needed to come to review the buddy procedures and check over each other's equipment.

Dealing With It: If you find that you're incompatible with another diver, ask the divemaster or other person in charge to change buddies, or join up with another diver or buddy pair on your own.

Lost Buddy

You're cruising the reef and turn to get your buddy's attention, but he isn't there!

Risk Factor: A lost buddy means the complete breakdown of the buddy system, and it puts both divers at risk for any number of situations including out-of-air, entanglement and other equipment problems.

Likely Causes: A lost buddy situation is more likely to occur when divers don't have clearly established roles and buddy system procedures. Low visibility, currents, equipment problems, distraction and differing dive objectives can also result in separated buddies.

Avoidance: The best way to avoid buddy separation is to adopt good buddy procedures and stick with them. Be certain to review the buddy system protocol with any new or unfamiliar buddy, just to make certain you're on the same page. This includes deciding where and how to join up after entering the water, and how the safety stop and final ascent will be managed.

Dealing With It: If you do become separated from your buddy, don't sweat it While there are variations in the standard procedure for a lost buddy, consider the following. First use an audible signal to attract your buddy's attention, spend no more than one minute completing a 360-degree turn (in case he's right behind you) and then make a controlled ascent to the surface to find him.

Unfamiliar Equipment

At the last minute, you find that a piece of your equipment is malfunctioning, so you quickly switch to rented or borrowed dive gear.

Risk Factor: The major risk factor in the use of unfamiliar equipment is being unable to cope with an abnormal or emergency situation that occurs during a dive.

Likely Causes: The primary causes that lead divers to use unfamiliar equipment is a loss or failure of their dive equipment, and then not taking the time to familiarize themselves with the rented or borrowed equipment prior to diving.

Avoidance: Before heading out on a dive trip, sort through all your dive equipment and make certain that everything is in good working order. Pack your dive equipment carefully.

Dealing With It: If you do end up using new or unfamiliar equipment while on a dive trip, take the time to thoroughly familiarize yourself with that equipment before diving. Run through a full function check in shallow water to make certain everything is working properly before heading to the depths. Also, make certain your buddy is familiar with your gear, especially your “safe second,” BC operation and emergency weight release functions.

Jammed Reel

You send up a marker buoy to let the dive boat know you're making a lengthy safety stop, when suddenly the reel jams, and you head for the surface like a hooked mackerel!

Risk Factor: Sometimes divers use a reel in conjunction with a surface marker buoy or safety sausage. The primary risk is being yanked or pulled to the surface if the reel jams during deployment of the buoyant device. Divers who make a rapid or uncontrolled ascent also face risk factors for DCI and AGE.

Likely Causes: The cause of rapid ascents associated with the use of line reels are primarily due to improper techniques and procedures. These include having the device clipped to themselves during deployment and gripping the reel too tightly.

Avoidance: The best bet is to get professional instruction before using a line reel to deploy a buoy or other buoyant device. In addition, a few simple rules apply: Never clip the reel to yourself during deployment, deploy slowly and downcurrent to avoid entanglements and make certain your buoyancy is properly set before deployment. If possible, anchor yourself while deploying a buoyant device with a line reel.

Dealing With It: If you do find yourself on the business end of a runaway reel, dump all air from your BC and flare your body to slow the ascent. If possible, cut the line free and let the buoyant device surface without you. If that isn't possible, follow the procedures for a blown deco stop if that scenario applies.

Entanglement or Entrapment

Swimming around a wreck, you decide to just swim in a short distance to get a better look, when suddenly you find you're tangled up and stuck!

Risk Factor: The primary risk in any underwater entanglement or entrapment scenario is running out of air. That is why it is so important to be prepared, to dive with a good buddy and to avoid situations that could lead to entrapment or entanglement.

Likely Causes: Entrapment scenarios often occur when divers choose to continue diving in an environment for which they are untrained and improperly equipped. Examples include divers who enter wrecks, caverns and caves without proper safety equipment and training. Such environments are extremely hazardous to the untrained diver. Entanglements can occur also on wrecks where fishing nets and lines may become caught and abandoned, and in areas of strong currents.

Avoidance: Common sense goes a long way in avoiding entanglement/entrapment problems. Never dive a wreck or other overhead environment without the proper training and equipment. Approach wrecks, caves, caverns, fast-moving water and other entanglement/entrapment hazards with extreme caution.

Dealing With It: Make all efforts to draw attention to your situation. Bang on your cylinder with a metallic device such as a knife to draw attention, or use an underwater horn or rattle. Remain calm and conserve your air as long as possible. If you become entangled use a safety sausage or SMB to signal for help if possible. If your remaining air supply is depleted and you cannot extricate your equipment from entanglement, as a last resort you may need to consider ditching your gear and making an emergency swimming ascent to the surface.

Many divers go their whole career without a serious complication or emergency, but it's always important to be prepared. This is why advanced and specialty training is so valuable. By continuing our scuba education and remaining mindful of the worst-case scenarios in our diving, we can be ready to cope with whatever comes our way.

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  1. Great article, informative read.
    Stumble upon this article whilst talking to her friend about scuba diving, got on the subject of emergency ascent, and he asked me how fast you rise to the surface, in the situation where everything has gone wrong. I seem to remember there was a formula or a General time frame for a uncontrolled buoyancy ascent, as in how fast you end up going. Am I misremembering that there is a rule of thumb or formula for that or am I just not being able to find it?
    And if it clear I'm not speaking of the recommended speed of ascent or even the emergency ascent, but runaway, completely uncontrolled- how fast would a person wind up going?

  2. Why isn't the purge valve mentioned under "wet breathing

    • Hello Kate,

      I will try to answer this for you...It depends on "why" your second stage regulator is breathing wet. An example: The housing has cracked and the purge would only push air through the cracked area, resulting in leaving the water in the regulator. There are several other reasons. However, I just had a customer bring a cracked reg housing to me and that is why I quickly thought of this as one reason! Anyway, hope this helps.

  3. I noticed in the "Wet-Breathing Regulator", that no mention was made to simply use your OCTO instead. If it is a torn diaphragm in your first, this should solve the problem.

  4. The annual DAN report makes great reading, for all these reasons.

  5. I really enjoyed reading this article. I never realized the value of breathing from a regular that is off to make sure you don't breathe air through a torn diaphragm or worn mouthpiece.

    I would add two little things:
    If you lose your buddy, look above you, at the surface. Your buddy might have lost his or her weights and is depending on you to retrieve them.

    Also, if you are breathing from a wet regulator, stick your tongue to the top of your mouth. Any water that enters will hit your tongue and not go into your lungs.

    Thanks again. I will encorporate all these points into any training that I teach.

  6. A good one to include for a Reel, is to never clip it to you BCD. You know it frees your hands. But, I had a buddy of mine that had his surface flag "Diver Below" retrieved, thrown in a small powerboat, and they drove away! My buddy was just fortunate that his line broke before he was injured.

    The "Blown DECO Stop" was a new one to me. I had in the past been told to return to depth and complete my Deco if that occurred. It is very good information, and could save injury.


    • Yes, generally the advice is not to return to depth to complete decompression, after a number of cases where divers did that, and subsequently passed out.

      • This is not accurate. Read the tdi or padi tec diver manuals. It depends on the stops missed and the time at surface. This topic is too complex and life critical to be treated in such a summary way. You should know better.

        • I was talking about a recreational dive at 20 metres. The Safety Stop is required. But, not always obligatory. A risk that one may take.

  7. A very clear and enjoyable article but I have one question. At the end of the Out of section you wrote: "As the ambient pressure decreases, more air may be available from the "empty" cylinder.". Can you explain this in a more elaborated way.
    Thank you JC

    • The "more air" part refers to the expansion of air as the pressure decreases. So while the air in the tank doesn't change in a technical sense, the amount of space it occupies upon leaving the tank and entering your lungs increases when the pressure on it due to depth decreases. It's similar to the idea that as you surface you shouldn't hold your breath because the air in your lungs expands or how the air in your BC seems to have a bigger effect as you surface.

  8. Nice but... about half can be prevented if you paid attention in training. If those are the 15 "Worst-Case Scenarios" then you have not dived enough.

    Good information to be reminded of, but your best guard against these situations is preparation, common sense, & calm.

  9. Excellent article that should be compulsory reading for all divers who like life. Some of the "nightmare" scenarios brought back memories of what happened to me in the last 35+ years of diving.

  10. In general, an excellent article. A couple of points:

    If a reel jams, let go of it! Better to be safe on the bottom than hauled up to the surface. If you're diving deep depths, carry a second spool and backup SMB just in case.

    If entangled, the most important thing is to keep calm and not to wriggle or try and push through it. If possible try and ease slowly backwards - it could be just a single fishing line that has fouled on your regulator. Be aware that monofilament fishing line is almost invisible underwater, so take care where you suspect fishing activities occur: Carry a sharp knife, or better still a Trilobite or similar cutting tool - you can often move the cutter (very carefully! Do NOT damage your equipment!) around where you feel restrained and cut the line if you've swum into it.

  11. Succinct and to the point....well presented.
    One of the more useful articles I've read on "What if".
    Much appreciated ~

  12. Very important to many divers like myself that due to short courses ,only know the risks when they occoured

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