Risk Assessment for SCUBA Divers – a holistic approach to diving safety

By Ed Zayas

Assessing risk is neither new nor a very complex discipline. In its simplest application, it is a lifelong mechanism for human protection and survival – one we practice every moment of our lives. It is also a process used in many industries to identify the risks associated with the daily operation of businesses, government agencies, and special projects or missions. My involvement with risk analysis began in the late 1980s, as a member of a military group engaged in the evaluation of computer systems at military and defense contractor facilities throughout the world. Later on, as a civilian contractor, I supported NASA in the evaluation and selection of automated tools and applications to facilitate risk analysis at the Goddard Space Flight Center. The tools used in risk analysis have evolved a lot since that time, but the basic concepts, theories, and principles are still the same. In this article, I will introduce four major components in risk assessment, in the context of recreational diver safety.

The four components 

The first component is a Hazard or Risk, which could cause some type of harm by its occurrence.

Let’s use a simple example – we are going to cross a street. What is a potential hazard we are exposed to when crossing a street? How about getting hit by a vehicle! And for the sake of simplicity, let’s not even think about the many types of vehicles we can get struck by (truck, bus, car, motorcycle, bicycle, etc.) 

The second component of risk assessment is Possible Loss – what could the consequence be should this hazard (getting hit by a car) occur. The consequence of getting struck by a car depends on many factors such as the speed of the vehicle, road surface conditions, and even the victim’s age. In some instances, the consequence may be the cost associated with hospitalization and lost wages, but in other instances the result could be loss of life, a catastrophic event indeed.

The third component is the Probability of Occurrence – how likely is this hazard to occur? This depends on whether we cross the street at a crosswalk or elsewhere, the volume of traffic at the time, and time of day or night. What’s the weather like today – is it sunny, foggy or raining? Let’s take it a step further. What are the age groups of individuals driving the cars on our particular road? Are they young? Are they old? What is the documented incidence of accidents in both groups? What do demographics tell us about people who live in the vicinity or those who commute on this road? And finally, what do statistics tell us about the number of accidents involving pedestrians in on this road.

The fourth component of risk assessment is called Mitigation. Mitigation means a range of things we can do in order to minimize the likelihood of this hazard occurring. In our simple scenario we could provide a level of mitigation by crossing at a crosswalk during daylight hours and when traffic is not heavy. We could also wear a reflective vest. For some of these mitigations we could assign a monetary cost. We can decide to spend $20.00 on the reflective vest to help minimize risk or we can simply accept the level of risk. If the level of risk was higher at a particular time we could simply decide not to cross the street.

For the sake of our example, it happens to be a sunny day and traffic is very light. According to statistics published by law enforcement, there have been few incidents involving pedestrians at this location in the past year. Also, there are many well marked crosswalks equipped with traffic lights and well-lit pedestrian crossing signs. Based on these facts it appears that we can cross the street in relative safety.

Now we need to decide how to best summarize the conclusions derived from our analysis of risk. For this we can use a qualitative or quantitative approach. In a quantitative approach, we use a numerical value to represent the probability of being struck by a vehicle. We would use an algorithm to calculate probability (# outcomes favorable / # outcomes) and take into account the many elements addressed previously like illumination, weather, volume of traffic, statistical number of accidents, where we cross, etc. It could look like this “10% probability.” In the qualitative approach we use terms like “Low”, “Moderate”, “Medium”, or “High” to describe the probability of getting hit by a vehicle. Regardless of which method is used, we now have sufficient information to put together a risk management plan to articulate how we plan to address all the potential problems which may arise from all the identified hazards and their probable occurrence.

When performing risk assessments, system security engineers organize hazards in closely related risk categories for a specific industry, business or operation. The evaluation of risk and recommended mitigation strategies should be performed by individuals with specific skills and experience. For example, in the field of Information Technology (IT), risk categories will address the physical and environmental risks associated with a computer system or facility (flooding, earthquakes, loss of power, fire, etc.) Physical risks to a facility are quite different from threats to a computing platform’s operating system or application software (introduction of computer viruses and other malicious software) and require careful consideration by experts in each respective discipline.

Now that we have laid out a foundation for risk analysis, let’s start defining categories of risk associated with SCUBA diving. Let me emphasize that the intent of this article is not to train the audience on the many types of accidents that can occur, or what to do (First Aid / CPR) when injuries and problems occur while SCUBA diving – that is the objective of Rescue Diver training. Instead, I would like to build a logical association of mishap categories to help us apply simple, common sense, mitigation strategies to reduce the risk for individuals engaged in SCUBA diving. Can all of this effort ensure that we will never suffer a mishap when diving? Of course not, but embracing a mitigation plan can certainly reduce the level of risk, and at the same time help us become better divers.

No doubt there are several ways of categorizing risk in SCUBA diving. I have come up with five categories that include underwater hazards, marine life, barotrauma, equipment failure and toxicity as a starting point to what I hope will become a positive exchange of ideas.


Underwater Hazards may be present anywhere we dive but are of greatest concern when entering or exiting the water from shore. These hazards are unique to each site. What may look like a sandy beach from shore can quickly change to an uneven or rocky surface with coral, fishing tackle, broken glass and other sharp objects, potentially harmful marine life and many more hazards present which may be difficult to spot if the water is murky. Heavy surf can add a substantial level of difficulty when entering and exiting the water as well.

Underwater hazards exist everywhere. I have come across fishing line, hooks and other tackle at the bottom of the ocean at many dive sites. I began SCUBA diving back in 1990 while stationed in Okinawa, Japan and remember occasionally coming across unexploded ordinance while diving off the island’s coast. If you ever come across any type of unexploded ordinance do not touch or try to handle it in any way. Make sure to report your finding to law enforcement.

Mitigation Strategies (Underwater Hazards)

  1. Find out as much information about the dive site in advance. Observe and evaluate the ocean and weather conditions when you arrive at the entry point. The presence of rip currents and tide information may help you determine the level of risk associated with your dive. You can find out information specific to a dive site by asking questions in online SCUBA forums. You can ask local dive shops for information as well.
  2. Minimize the amount of equipment you are carrying such as cameras, spears, nets, etc.
  3. Wear hard sole booties when making a shore entry and walk in using a shuffling motion with your feet. The vibration caused by this movement should alert sea life of one’s proximity, alerting them to move out of the way before you step on them.
  4. In light surf, get in the water with all your equipment on making sure your BCD is inflated. As soon the water level is slightly above your waist, put your second stage in your mouth, put on your fins, and get horizontal on top of the water, lessening the chance of stepping on any underwater hazard and keeping you from getting knocked over by slipping on uneven rocks.
  5. With calm ocean conditions and clear water, using a snorkel during your entry from shore is a good idea. Think about all the air you will save as you make your way to your descent point in deeper water – air you can use to enjoy your dive a little longer. If the surf is rough, then you should put on your fins before entering the water and enter or exit the water sideways or facing back while holding on to your dive buddy.
  6. Trim your gear – make sure there are no dangling pieces of equipment like your octo, gages or computer.
  7. Carry a dive knife/tool or other device to cut entanglement material.


One of the reasons I SCUBA dive is to observe marine life in their habitat. As a diver who is passionate about conservation of the environment and marine life, I practice a few important rules when approaching all marine life to minimize the risk of harm to them and to myself. Most marine life injuries stem from an animal’s natural response to a perceived threat, a simple defense mechanism for their preservation. Such attacks and injuries are a response to something we have done either on purpose or accidentally.

Wiggle a finger in front of a moray eel and you may find out how vicious and painful their bite can be. Ah, but the turtle seemed so friendly – what could possibly go wrong by sticking a finger in front of it. Well, the cute little turtle can easily remove that wormlike finger from your hand with surgical precision. In spite of all the training and great advice from dive instructors and seasoned divers, some individuals seem to lose all sense of reason when diving and get injured.

Not all marine life injuries are the result of provocation. While unprovoked attacks by marine life are rare, they can result from inadvertently touching an animal or organism. Examples of unintentional physical contact with sea life are brushing against jellyfish, stepping on an urchin, stonefish or stingray, or bumping onto a scorpionfish as all of these can be hard to spot. We could also get cuts and scrapes by brushing into coral or barnacles.

Marine animals can be inquisitive at times too. A few months ago, a beautiful lemon shark followed me to the surface after a wreck dive, coming within 4 feet of me. I just remained suspended in the water column while completing my 3-minute safety stop mesmerized by the beauty of this animal. The shark was so close I could have swum towards it and touched it. Why didn’t I? As I said previously, an important part of my dive ethic is to “respect all marine life”. Even though I didn’t get to touch that shark, the memory of that special moment remains vivid inside of me. Most important, I experienced that moment without harm to the shark or myself. 

Mitigation Strategies (Marine Life)

  1. The most important way to minimize the risk of being harmed by marine life is to treat all creatures with respect. It’s not nice to touch or engage in harassment of any animal – keep a safe distance and your hands to yourself or better yet, on your camera so that we can enjoy your photos or video.
  2. Develop and practice good buoyancy skills – stay off the bottom.
  3. Wear adequate protection for your feet and skin that is consistent with the water temperature and environment.
  4. Always be aware of your surroundings, 360 degrees horizontally, below and above. I know of a diver taking pictures while buoyant above the bottom when a young adult landed on her back at depth, pushing her onto the bottom and causing her to land on top of an urchin. No matter how many safeguards we put into effect for our safety, there is always a chance that an accident will occur.

A few recommendations related to hunting underwater. 

  1. Handling of spears on a dive boat, during entry into the water and exit present a higher level of risk. Grab your spear gun at the back of the boat before entering the water with the bands are undone and its safety on until you are underwater and ready to shoot. When getting back on the boat, hand your speargun to the boat’s divemaster with the bands undone and its safety on before climbing back on.
  2. Sharks will be aroused by more than the smell of blood – the sound made when the shaft is released will also get their attention.
  3. Whatever you catch i.e. lionfish, can still sting you even after you are back on the boat. Place your catch in a container that is appropriate to ensure your safety and that of your fellow divers.

Other comments and additional recommendations I leave to the hunting experts.


Barotrauma refers to injury to the human body because of pressure related changes in different body compartments. Examples of this are Decompression Illness which includes Decompression Sickness (DCS) or “the bends”, Arterial Gas Embolism (AGE) and other types of lung expansion injuries such as Mediastinal, Subcutaneous or Pneumothorax emphysema. These are some of the most serious risks associated with SCUBA diving. We need to be cognizant of the causes which lead to these events and develop both diving disciplines and lifestyles that will minimize the risk of these injuries happening to us.

Body Cavity Squeezes (Ears, Sinus Cavities, Teeth, Mask and Wetsuit) are also related to barotrauma. A squeeze takes place in unequalized air spaces in our bodies like the middle ear, sinus cavities or teeth. These issues can quickly turn into an emergency underwater with consequences ranging from mild discomfort through excruciating pain and damage to our eardrums or teeth. A squeeze can also happen in the air space inside your mask, hood and wetsuit as the air inside these is compressed during descent. A mask squeeze occurs when we don’t exhale through our nose into the mask during our descent. In the case of teeth, gas spaces underneath a cavity or filling will compress during descent with the potential to implode, and to explode upon ascent as gasses expand. As you can imagine, this could be very painful.

Mitigation Strategies (Barotrauma)

The following are lifestyle/general recommendations to help us diminish the likelihood of experiencing barotrauma.

  1. Stop smoking or vaping – this is a clear choice you must make, one that nobody else can make for you other than offering encouragement. Yes, I fully understand how difficult quitting can be. I quit smoking 15 years ago.
  2. Exercise regularly. I walk, jog, or ride my bicycle twice a day. Your level of exercise depends on your age and existing level of fitness. Always seek advice your physician’s advice before engaging in a fitness program.
  3. Observe a healthy diet. Be nice to your body by making good choices about what you eat.
  4. Hydrate. Not just in preparation for a dive but as part of your daily routine. Our body tissues and organs need water to function properly, to remove toxins / impurities, and lubricate joints. How much water you need in order to stay hydrated depends on the climate, your level of activity and physical condition, and even your age. As a general rule, you should drink at least 6 to 8 glasses of water every day. If you don’t practice good hydration habits, then begin hydrating the day before your dive – don’t wait until the last minute.
  5. Take good care of your gums and teeth. Visit your dentist and make sure your mouth is free from cavities.

The following mitigation strategies are more specific in nature.

  1. Don’t dive when you have a cold, chest, nasal or sinus blockage or congestion.
  2. Plan your dive and dive your plan. At the time of your dive you can make last minute modifications taking into account visibility, ocean currents and overall weather conditions.
  3. Analyze your gas mixture to make sure it is what you plan to breathe during your dive. Telling your dive computer what mix you plan to use does not magically change the mix in your tanks.
  4. Stick to the depth and duration time limits established by your dive computer and dive tables for the mix of gasses you are breathing and don’t push these boundaries. Whenever possible shave off a little time, giving you more time during your ascent – be conservative! That wreck, reef or cave will still be there tomorrow … and the next day as well so you can come back and explore it again.
  5. Watch your ascent rate. Most dive computers will give you a visual indication when you are ascending too fast. If you find yourself without a dive computer remember not to ascend faster than the slowest bubbles around you. The recommended rate should not exceed 30 feet per minute.
  6. Perform a safety stop. At the end of every dive (not including training dives in shallow water) you should stop at a depth of between 15-20 feet for a period of 3 to 5 minutes. This is NOT a decompression stop but an important mitigation step to help reduce the risk of getting decompression sickness. I do not recommend performing the safety stop at a depth shallower than 15 ft. The reason is that sometimes, wave through to crest variance can be substantial, quickly changing your pressure level. Remember that the greatest changes in pressure occur at the very top of the water column. In addition, being that close to the surface places you at greater risk from boat traffic even when you have deployed a safety sausage.

The following mitigation strategies address problems related to squeezes.

  1. During your descent, don’t wait until you feel pain to start equalizing your ears. Always start equalizing at the surface before beginning your descent on the water column. Use whatever technique works best for you. I use both a gentle application of the Valsalva maneuver and horizontal movement of my jaws.
  2. Exhale through your nose during your descent and throughout your dive.
  3. Gently pull on the corners of your hood to allow water to circulate during your descent.


I am going to define two hazard categories associated with equipment failure. The first one addressing hazards associated with improper fit of dive gear to include booties, fins, wetsuits and drysuits, hoods, masks and gloves. For example, fins that fit too tight may blister your skin while a fin that’s loose will require a lot more effort during your kick and may come off during a giant stride entry. You should also adjust your mask so it’s not too tight on your face, allowing you to exhale through your nose during your dive to relieve pressure, to adjust it if needed, and to clear water out. A tight seal on your hood or seal around your neck can reduce your blood circulation or blood pressure, resulting in dizziness and even worse, causing you to blackout and drown.

The second type of equipment includes dive computers, buoyancy inflators, tanks, valves, manifolds, bands, first stage, second stage, octo, and out of air situations.

Mitigation Strategies (Equipment Failure)

  1. Make sure your equipment fits properly and comfortably. I prefer to purchase dive gear at a dive shop. There is always someone there to help me chose gear that fits properly. Other items I can easily order from an online store but when it comes to wetsuits, mask, fins, hoods and gloves I prefer to try these on to make sure they fit properly.
  2. SCUBA tanks require a visual inspection (VI) once a year and a hydro test every five years. A dive shop will typically check the date of your last VI every time you bring a tank in to be refilled. The date of your tank’s last VI is punched into an adhesive sticker bearing the name of the diveshop that performed the inspection. When a hydro test is performed the date of the test is stamped on the tank as a visual reminder.
  3. When you bring a tank in for a VI, most dive shops will also clean the tank’s valve. Ask your dive shop to make sure this is done at the same time your tank undergoes its VI.
  4. Support a local dive shop. Find a dive shop and develop a good relationship with them. Bring your gear in and ask them when it should be serviced. Each brand will establish their own frequency of function checks and inspection standards. You should take into account how often you use your gear. I prefer to have my BC inspected once a year and my first stage, second stage and octo every two years.
  5. Take good care of your gear – you would be surprised how much longer your gear will last by just rinsing it with fresh water after every dive and allowing it to dry before storing it. Fill your BC’s bladder with fresh water, blow air into it and flush salt or pool water out of it two or three times. Once you have done this, fill the BC with air before storing it. Do not allow water to get into your first stage!
  6. Check the battery charge on your dive computer before and after every dive. I replace my battery whenever it reaches 50% charge.
  7. If you use doubles have your dive shop check and clean your valves and manifold every time you VI your tanks.
  8. NEVER lift your doubles using the manifold as a handle. If you are diving on a boat bring your doubles onto the boat on your back and remove them the same way. Do ask the crew to use the valves to lift your tanks and not your manifold. I use HP 100’s on my double rig so few crewmembers will handle them.
  9. Remember that service kits for your equipment may not be available forever. If you bring in a first stage, second stage or octo to a dive shop to be serviced and the equipment is 10-15 years old then there is a good chance that service kits will no longer be available. And try not to bring your gear in to be serviced a week before you need it. Service kits may take a few days and sometimes longer to get a hold of, and you may end up having to take your gear as is (not recommended) or renting a set from a dive shop.
  10. Start monitoring your air supply as soon as you get to the bottom and regularly during your dive. Ask your dive buddy occasionally how much air they have left. Begin your ascent making sure you will have enough air in your tanks to complete 3-5 minute safety stop, inflate your safety sausage and remain on the water with your regulator in your mouth until you board the boat. Plan on climbing back on your boat or completing your shore dive with a pressure of at least 500 PSI left on your tank.


Oxygen toxicity poses a risk to nitrox divers. In SCUBA diving, toxicity is the extent to which a gas is poisonous to the human body. Two types of oxygen toxicity are pulmonary and central nervous system (CNS). Pulmonary oxygen toxicity is caused by exposure to elevated partial pressures of oxygen over long periods of time. This is referred to as time-dose exposure and is mostly associated with technical diving and exposure over prolonged dives.

Pulmonary oxygen toxicity is not as much of a concern in recreational diving activities where nitrox is used. The reason for this is shorter exposure times when following the “No Decompression Limit” (NDL) guidelines, along with typical adherence to recommended surface intervals.

Central Nervous System Oxygen Toxicity is what recreational divers should be mostly concerned with as it occurs breathing oxygen at an elevated partial pressure can affect the central nervous system. An effect of CNS oxygen toxicity is convulsions. When convulsing under water, an affected diver can lose his/her regulator, and possibly drown.

By planning our diving depth, observing Maximum Operating Depth (MOD) limits, and diving conservatively, we can substantially decrease this risk.

Mitigation Strategies (Oxygen Toxicity)

This article is written with the recreational diver in mind. For the purpose of this assessment I will focus on our recreational divers who use Enriched Air Nitrox (EAN). I make no reference or recommendation about gas mixtures or decompression stops. Instead I will address the importance of adhering to the Maximum Operating Depth (MOD) or depth at which the partial pressure of oxygen in a specific EANx mix exceeds its acceptable limit.

Suppose we are using an EAN34 mix for our dive. First, how do we know that the gas in our tank has a mix of 34% Oxygen? Because the dive shop put a label on the tank that says 34%? Hmm … I have my tanks filled at a very reliable dive shop but I take diving seriously, so I analyze my tanks before picking them up to see what my mixture is. A reputable dive shop will maintain a logbook where customers enter the result of their mixture analysis.

What is the Maximum Operating Depth for EAN34? We can use one of many apps on our phone to calculate the MOD but we should also know how to figure this without the help of an electronic device. The formula is very simple.

 ((Maximum partial pressure of oxygen / percentage of oxygen in tank) – 1) x 33 ft

Note that most organizations involved in SCUBA diving recommend using 1.4 ATA as the limit for Partial Pressure of Oxygen (PpO2) so our formula is going to look like this:

MOD = ((1.4 ata / .34 ata) – 1) x 33 feet

Now let’s do the math: MOD = ((4.12)-1) x 33) = 3.12 x 33 = 103 feet

In this example the Maximum Operating Depth when using an EAN34 mix is 103 feet.

  1. Analyze your gas mixture to make sure it is what you plan to breathe during your dive. It does not matter what the label on the tanks says – be a responsible diver and analyze your own gas mixture.
  2. Based on your analyzed EANx mixture, calculate your MOD.
  3. Make sure your dive buddy knows your planned MOD.
  4. Check your depth occasionally during your dive and stick to your MOD. If you are willing to accept the risk of calculating your MOD using a maximum PpO2 higher than 1.4 (such as the generally accepted 1.6 contingency) then be prepared to accept the consequence of your decision.


Carbon monoxide (CO) poisoning has injured and claimed the lives of many individuals around the world. This gas has no color, odor, or taste. Back in 1974 while stationed in Seoul, Korea I remember the news of a fellow soldier’s death due to carbon monoxide poisoning. He had decided to spend the night with his girlfriend at her house in the local village. The house’s heating system relied on charcoal cylinders placed under the homes. During the night, carbon monoxide leaked through the floor into the bedroom. The soldier and his girlfriend died in their sleep. 

Carbon monoxide poisoning is an issue of great concern in the SCUBA diving industry. The greatest problem with carbon monoxide is that it bonds with hemoglobin in our blood easier than oxygen at the molecular level preventing oxygen from making its way through the bloodstream to our vital organs and tissue. CO can make its way into our SCUBA tanks through a poorly maintained compressor or inadequate placement of a compressor’s intake.

Mitigation Strategies (Carbon Monoxide Toxicity)

  • Have your tanks filled at a reputable dive shop, by qualified technicians.
  • Although carbon monoxide is odorless, the gas is often introduced with other contaminants that could have a smell. One example is the smell of car exhaust. As you check your equipment in preparation for a dive, purge air through your regulator’s second stage and smell its content. If there is any smell, I would not use the tank.
  • If during a dive you experience symptoms like dizziness, headache, nausea or vomiting, shortness of breath, or blurry vision you should terminate your dive immediately. There is a good chance that you are already suffering from carbon monoxide.

Now that we have a fairly comprehensive framework to mitigate risks associated with SCUBA diving, let’s decide what our risk management plan will be to help reduce the risk of a mishap, to become self-reliant divers. Our strategy could consist of taking better care of our bodies by observing good eating habits or exercising.

Another component of our RMP should be training. I recommend that you enroll in a Rescue Diver course. There are many great providers – I happen to be very happy with the knowledge and skills learned through SDI/TDI rescue diver training.

There is so much more to be explored and discussed in regard to risk assessment in the SCUBA diving industry! The risks associated with the operation of dive boats and a brick and mortar diveshop that provides gas refills, equipment sales and repair, and where SCUBA training is conducted are quite different and more complex.

I look forward to exploring and writing more articles about this important topic. Until we meet again, dive safely!

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