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Diving Accidents in Swimming Pools

Marc Green

Dives into swimming pools are a major cause of serious injury. Although some states have enacted laws restricting liability actions related to diving, it is still a common source of litigation. Unfortunately, issues involved in swimming pool accidents are not always obvious. In this article, I provide a primer about diving accidents in swimming pools. Much of the discussion directly transfers to diving accidents in rivers, lakes and other natural settings.

Swimming Pool Design

Depth

Often, diving accidents are attributed to insufficient water depth at the point of the dive. Statistical analyses show that the vast majority of accidents occur in water depths of about 3 feet or less. One study reports only 13% of accidents occurred in depths of 3 -9 feet.

Since injury often occurs with head impact on the pool bottom, depth matters because water acts as a brake that slows diver velocity. Several diving biomechanics studies examined the velocity of divers as they enter the water and reach various depths. People diving from boards and decks hit the water at about 15 feet/sec. Estimates of the point where downward motion ceases is between 12-15 feet, although others place the depth for absolutely safe diving at 18-20 feet. Of course, few can pay the expense of building and maintaining a pool of such depth. This leaves open the question of the water depth required to create an acceptable risk.

It has proved surprisingly difficult to determine the depth of water required for safe diving. The recommended minimums cover a wide range, from the American Red Cross and FINA (Federation Internationale de Natation Amateur) estimates of 3 feet to the Australian Diving Association estimate of over 9 feet. SportSmart Canada recommended diving only when the depth is twice diver height. Many standards do not discriminate among diving platforms, although the National Foundation for Spinal Health specifies a minimum 3 1/2 feet for any diving, 3 1/2-4 feet for dives from platforms of 18 inches above the water and 4+ feet for platforms up to 30 inches high.

It is important to note that such estimates are merely "standards" and are not based on any physical, empirical science. Moreover, accident statistics are of little help. The fact that most accidents happen in 3 feet or less of water does not provide a true estimate of risk. There is no way to know how many safe dives were taken at each depth and hence there is no way to know the probability of injury for water at each depth. There are no baseline controls on these surveys, so they are not scientific data. (Very few accidents occur in water depths below 2 feet. This is likely not because of greater safety but because relatively few people dive into such depths.)

Lastly, safe depth depends at least partly on dive angle and technique. It is likely that short of making pools so deep that all vertical motion ceases, maybe 15 feet, there will never be an absolutely safe depth for all divers. Moreover, issues of pool shape also can affect safe diving depth.

Shape

1. Bottom Contour

Although some accidents occur when the diver's head strikes bottom, others occur when the diver's trajectory runs him/her into an underwater contour. In most pools, there is a gradual slope to the bottom. For in-ground pools, this is intentional in order to gradually change depth from the deep end to the shallow or because there is a diving well, an area made especially deep for diving. For an above-ground pool, this is usually inadvertent, occurring when the middle of the bottom is dug deeper than the area around the edge. The result is a deep spot in the middle of the pool with grades going up to the sides. If the bottom grade is steep, it is sometimes called the "spinal wall." Collision with the spinal wall is a frequent injury cause and is probably the main cause of accident for dives in deeper water.

Another factor in such accidents is the absence of water depth markings. This not only makes judging depth at the dive location difficult, but also prevents a diver from estimating how quickly dive angle will bring him/her into shallow water. Even when markings are available, they are often located underwater where they are difficult to see.

2. Side Contour

Injuries sometime occur when the diver hits the side of the pool. In this case, it is often pool width rather than water depth that causes the injury. Pools with irregular curved outlines may leave insufficient margin-for-error if the diver's movement takes him/her laterally.

Presence/Absence of A Diving Board

It is generally thought that pools with diving boards hold a greater potential for danger. Depending on the spring constant, the board catapults the diver higher into the air, causing falls to water from a greater height and possibly with control loss of dive angle and direction.

However, diving boards also have a potentially beneficial effect. Most people have a mental model of a swimming pool as having both a shallow end and a deep end and know that it is safer to dive in the deeper end. The diving board acts as a cue which directs the pool user to the safe location to dive, so it is less likely that someone would then inadvertently dive into the shallower end. (Of course, absence of a diving board could be taken as a cue "not to dive." However, most people are aware that pools often do not have boards for insurance and litigation reasons rather than because the water is too shallow. So board absence is a relatively weak cue for "no diving.")

Warnings and Compliance

While several studies suggest that warnings can reduce diving injuries, there are many factors which affect likelihood of seeing and complying with warnings. On another page, I have discussed general matters related to warnings. Here, I will just add some issues specifically related to diving.

Noticing The Warnings

One study examined whether a group of high school students would notice "No Diving" signs located in 3 places around the shallow end of an in-ground pool. The majority of students failed to notice the signs, with females being significantly less likely. (This runs contrary to studies for other products, which generally shows females more likely to see warnings.) Interestingly, males were still more likely to dive into the shallow end.

Risk Perception

Several studies have shown that people with a history of diving into both in-ground and above-ground pools were more likely do so in spite of the warning. This is the "familiarity effect," where people having a benign history with a product are less likely to comply with warnings. Since their personal experience says that there is little risk, they are more likely to gauge future risk as low. Ironically, the most experienced and able divers, such as swim team members, are the most likely people to ignore warnings.

The finding that most accidents occur on a first dive of the day may also be a type of familiarization effect. However, it may also be a statistical anomaly - there are probably more first dives taken than second, third, etc. Moreover, people injured on a first dive will not have the opportunity to take subsequent ones.

Visual Factors

Accidents often occur because visual factors make depth estimation difficult. Lack of lighting around a pool has been estimated to contribute to about 30% of diving accidents. Another more subtle effect occurs because of water's optical properties, which affect depth perception. When a diver looks into a pool s/he is likely to overestimate the depth because water in the pool bottom will appear to be farther away than its actual distance. This effect is magnified by any cloudiness to the water, which often results from poor maintenance or other sources.

Diver Sense of Control

People may be well aware of a hazard, but believe that they can minimize risk by using a product in a "safe" manner. Many accidents occur when a diver is aware that the water is shallow but decides that it is OK to dive if the trajectory is shallow. In fact, most people have poor control over dive angle.

Social Factors

People often model their behavior based on what other people around them are doing. If other people are diving into a pool, then there is increased likelihood that warning signs will be ignored.

Conclusion

I have provided a brief overview of issues related to diving accidents. This is a subset of many more general issues, which are discussed in Warnings and Warning Labels. However, warnings are only one of the issues involved. Should there be a diving accident, here are some of the questions which should immediately come to mind:

  • What warning signs were present?
  • What was the water depth?
  • What was the pool width?
  • Was there a spinal wall?
  • What were the lighting conditions?
  • How clear was the water?
  • What was the diving experience of the injured party?
  • What were other people at the scene doing?


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