Computerised anti-drowning system for public swimming pools
On the 3rd October 1995, the Mayor of Geneva, Monsieur André Hediger, inaugurated the first avant-garde anti-drowning safety system in the world. Known as SPY, short for Swimming Pool eYe, this automatic scanning system continuously examines the bottom of the pool, without human intervention, and sends a warning to the pool attendants should an individual find himself in danger. This device, which was thought up following a fatal accident in 1992, was the subject of extensive development by the IEM SA company of Geneva, working in co-operation with the Sports Services Department of the city of Geneva. The device has been patented.

Introduction
Our modern company has installed a network of swimming pools, used for training our young, where everybody can spend some time relaxing, playing games or engaging in sporting activities. These areas, especially the swimming pools, are certainly amongst the best supervised. Each swimming pool has 1, 2 or even 3 attendants for 10, 40 or 80 people enjoying themselves in the water. And yet, despite all the attention and professionalism of these attendants, complete areas remain outside their field of vision and accidents - sometimes even fatal - do happen. In fact, the strong lighting and wavelets form reflections which prevent the attendants from seeing everything that is happening under water. The SPY system is the tool provided by modern technology to improve the supervisory services provided by the attendants, initially by monitoring the invisible areas and then by automatically and systematically analysing these continuously by computer. All this happens without exception.

A study involving those parties insured with the National Swiss Accident Insurance Company showed that 5,240 accidents involving swimming or water sports occurred over a period of 3 years. 2.8% of the latter were fatal, 34% of accidents happened in swimming pools, 23% in lakes, 21% in open water (ponds), 12% in rivers and 10% were miscellaneous.

Drowning
When a person is in difficulties in the water, or is conscious or unconscious following exhaustion, or loses consciousness following sudden immersion in cold water, or suffers a heart attack or even a knock on the head, then the rate of carbon gas increases until it passes the tolerable physiological limit. When this happens, a self-preservation reflex action occurs which cannot be controlled by the brain, namely the medulla oblongata forces the subject to breathe. In a water medium, the lungs fill up with water and the individual immediately sinks to the bottom of the pool.

Monitoring the bottom of the pool
The underlying principle of supervising the pool is to monitor the bottom only, with a view to ensuring that there are no motionless bodies lying there. To this end, the lower periphery of the swimming pool walls was covered with a series of light and dark tiles arranged alternately, constituting a pattern which can be clearly identified by eight submerged cameras. Recognition of this pattern, based on an algorithm derived from spectral analysis (Fourier analysis) serves as a basis for continuously measuring visibility which permanently answers the following question: "Is the opposite wall completely visible?" As soon as a section of the wall - at least 40 cm wide - stops being visible for more than 25 seconds, the system automatically alerts the pool attendants.

The alarm is sounded by an audible gong to attract the attendant's attention. At the same time, a series of lights are triggered to show what area of the pool is involved. To date, the system has, without failure, automatically detected a diver who simulated a drowning person, swimmers who were suffering from apnoea or even items such as a cleaning robot. By concentrating its monitoring on the contrasting areas of the opposite wall, rather than attempting to identify the actual swimmers, the system operates independently of the ill-timed alarms which are triggered by the strong fluctuations in light caused by the sun's rays, the shadows cast by the swimmers or even the surface wavelets. In extreme cases, such as strong water turbidity or inadequate lighting - such as in the case of a storm or dazzling of the camera - the system spontaneously switches off and by way of a red light, indicates to the attendants which area of the pool is temporarily unsupervised.

Economic considerations
The cost of the automatic SPY detection system represents 2 to 3% of the attendant's costs for an Olympic standard swimming pool. It is, in fact, a very small sum compared with the value of a human life which cannot be estimated and the dreadful publicity surrounding the swimming pool every time someone drowns.

Conclusion
The task of the pool attendants has not changed as a result of implementing new technologies. Its main purpose is still to be ready to help in the event of an alarm, whether this is raised by other pool users, by the SPY detection system or by the pool attendant himself. This automatic system is an aid which provides a considerable improvement to the quality of supervision offered but which could never be used to replace it. To conclude, these few words from a pool attendant, who was on duty alongside the pool on a sunny summer's day, sum things up: "SPY is our best friend - it's most distressing and unnerving to observe things without seeing them, whilst our moral obligation demands that we see everything, and the swimming public firmly believes that it is being supervised."

Sport accidents 29.2 by Kurt Biener, Verlag Hans Huber Bern Göttingen Toronto