The human factors of diving accidents in pools: Diving accidents in swimming pools often cause serious injury This is somewhat surprising, in view of the widely accepted belief that diving is an inherently dangerous activity. Some states have even enacted laws restricting lawsuits related to diving, the rationale being that diving is an open and obvious hazard, so divers accept the risk - Aquatics

So why do accidents still occur with such regularity? 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.

The causes of accidents lie in two sets of factors. The first is physical, the pool design. Some are inherently safer than others, but, as explained below, none can be perfectly safe. The second set is psychology and human factors. Some factors are due to visual attributes of the pool environment, but most center on the way people see warnings, view risk, and decide on compliance. Below, I discuss the issues involved in each set of factors.

PHYSICAL FACTORS

The safety of diving varies with several aspects of 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 1/4 feet or less. One study reports only 13% of accidents occurred in depths of 3 1/4 -- 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/second. Estimates of the point where downward motion ceases is between 12 -- 15 feet, although some 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.

The answer to this question has proved surprisingly elusive. The minimums recommended by various sources cover a wide range, from the American Red Cross and FINA (Federation Internationale de Natation Amateur) estimates of 3 feet, compared to the Australian Diving Association estimate of over 9 feet. SportSmart Canada recommends 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 plus 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 or empirical science. Moreover, accident statistics are of little help. The fact that most accidents happen in three 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 at each depth. There are no baseline controls on these surveys, so it is not scientific data. (Very few accidents occur in water depths below two feet. This is likely not because of greater safety, but because relatively few people dive into such depths.)

Lastly, safe depth depends at least partially on dive angle and technique. It is likely that short of making pools so deep that all vertical motion ceases, at approximately 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:

-- 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 end or because there is a diving well, an area made especially deep for diving. For above-ground pools, this is usually inadvertent, occurring when the middle of the bottom is dug deeper than 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 diving accidents 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.

-- 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. Artsy pools with irregular curves are becoming increasingly popular, but may leave insufficient margin-for-error if the diver's movement takes him/her laterally.

PSYCHOLOGY & HUMAN FACTORS

Regulatory bodies require swimming pool managers to post warnings about the safety of diving conditions. However, people frequently fail to notice or to comply, and accidents ensue. Reduction of diving accidents requires an understanding of how people respond to warnings and why these warnings so often fail.