Almost half of divers have gone missing in the water at some time or other, for an average of 30 minutes. That, at least, was the result of a survey we carried out with diving club members. Its worrying, but carrying a surface marker aid can reduce the risk of your cover boat missing you, and increase the chances of you being rescued if you do get lost.
The range of primary devices includes telescopic flags, surface marker buoys, torches, strobes, pyrotechnics, whistles and fluorescent dye. Some have been trialed by manufacturers, and groups of divers have conducted independent assessments (as in The View from the Chopper, Diver, July 1997). Much of this work has provided qualitative information, but there has been a need for more extensive and quantitative evaluations, particularly under different conditions.
The Health and Safety Executive was concerned about incidents involving missing or lost divers on commercial diving projects, and contracted Heriot-Watt University to undertake a study. We wanted to find out which location aids would get divers noticed on the surface, whether any device was significantly better than others and which shape, size and colour was most readily sighted by observers on a cover boat.
We looked at: yellow, red, orange and black folding flags from Bowstone (15), and an A-Flag; Polyform buoys (5), Bowstone Self-Inflating Decompression Bags (120), AP Valves (30) and Bowstone (15) delayed surface marker buoys; Underwater Kinetics MiniQ, SL4, UK400, UK1200 torches (15-150); Seeman Sub Signal Flash (22) and Jotrun AQ-4 (70) strobes; Pains-Wessex Miniflare 3 pyrotechnic rockets (27) and Day/Night Distress Signal flares and smoke (32); and Sea-Streak (15) and Presto Dyechem (14) marker dyes.
We also tried out a PLB7 EPIRB, a model since upgraded by Sea Marshall Rescue Systems. We consider an EPIRB to be a secondary emergency location device to be used as a last resort, and our study focused mainly on devices that would help spot a diver as soon as he or she resurfaced. Our findings are not included here, pending possible legal action on the part of the manufacturer.
Searches were carried out from inflatables and hardboats, as well as RNLI lifeboats and a search and rescue helicopter, in Scapa Flow between January and March. We certainly got the range of weather we needed, with one session carried out in winds gusting to 45mph.
To find the maximum distance at which the various devices could be relocated, we secured them to weighted shotlines and recorded their position with a GPS fix. When an observer on the search vessel sighted it, another fix was taken to calculate the relocation distance.
A variety of strategies was used to simulate real search conditions and ensure, as far as possible, that direct comparisons could be made under comparable conditions. At or close to sea level, devices were tested under sea states from calm to marginal and a broad range of light intensities.
As these conditions deteriorated, we found, location distances of devices at sea level that did not provide an artificial light source decreased correspondingly. The aspect of a device above sea level and its colour also had a bearing, and the observers eye height had a pronounced effect.
A fully kitted diver without any additional location aid was located at between 250m and 700m under ideal conditions. The upper distance was recorded with the diver raising his arm. We also measured the distance at which the diver could see the boat by deploying a diver on a shotline as the boat moved away.
In daylight with a wave height of 0.5-0.75m, the diver lost sight of the inflatable at 1300m and the hard boat at 4400m. So a diver without a location aid can see a recovery vessel some time before it is close enough to locate him.

The folding flags were by far the most reliable and, at about £15, cost-effective location device we tested, particularly the day-glo yellow pennant, which was consistently spotted at more than 2km and up to 3km. Yellow was the most conspicuous colour in all sea states, even with breaking wave crests, and could be located in deteriorating light when it was impossible to locate pennants of any other colour.
Red and orange flags were located at up to 1600m. Two of our observers suffered from degrees of red/green colour blindness and had difficulty spotting these colours, particularly in intermediate light conditions. The A-flag performed least well in all conditions. Not surprisingly, flags were most easily located when the search heading was abeam to the wind direction, so that the pennant presented the greatest visible surface area.

Location distances of the SMBs were similar - up to 1200m. The Bowstone Self-Inflating Decompression Bag had a slight advantage, in that it came in day-glo orange/red and was brighter than the AP Valves and red Bowstone decompression sausages. It was difficult to make a positive identification until the observer got much closer than the initial sighting, because at a distance this device resembled a single red creel buoy.
Several observers found that the AP Valves sausage was easier to locate than the red Bowstone version, being slightly wider and taller. Most found the Bowstone sausage, which was a dull yellow, difficult to locate, but the location distances were not significantly lower than the other SMBs.
An SMB is invaluable as a location aid on wreck, drift and decompression dives. If sausage-shaped, it should be wide and stand tall above sea level. Self-inflating deco sausages should retain their form at the surface for some time under adverse sea states. Decompression markers might provide increased location distances if they were made in the same day-glo yellow as the folding divers flag.
Paired red Polyform buoys, the sort often used as permanent SMBs, provided location up to 1100m and were much easier to relocate than a single buoy, especially where single creel buoys of similar size and colour were found. The separation distance between them meant that they would yo-yo under increasing wave heights, so that at least one buoy usually remained visible.
We would recommend that such paired buoys be at least 40cm in diameter, with at least 2m between them. Divers using any marker buoy from which they might become separated should always carry a secondary device, such as a flag.

The diving torches produced very bright beams and were clearly located during daylight at more than 4km, increasing to beyond 9km in darkness. Their location was restricted when the diver thought that they were pointing directly towards the search vessel, but when moved slowly but steadily in a scanning motion (both horizontally and vertically), they could be detected over a wider sector. This also avoids temporarily blinding the skipper at close range.
Using a torch as a signalling device is strongly recommended, but we would recommend that one be kept in reserve for the purpose, because the unit used during a dive might not have the power needed.
We used the strobes only by attaching them to the top of folding flags. We know that when attached to the shoulder of a divers BC, the visible flash is extremely intermittent as waves lap over and around it.
The strobes were not observed until the light was very low, the Jotrun at distances up to 4km but on average at around 2km. It appeared to generate a more intense flash and to be more effective than the Seeman Sub strobe.
A high-intensity, good-quality strobe should always be carried when diving in low light levels, but it needs to be mounted as high as possible. We would recommend that divers carry two if they are to be primary location aids.
Any electrical device, such as torches or strobes, must be reliable and robust if it is to be relied on as a marker buoy. Regular, thorough inspection and maintenance is needed, with special attention paid to sealing surfaces and O-rings.
Our staff frequently use torches and strobes in normal diving and have found supposedly high-quality devices as prone to leaking as lesser-quality models. The reliability of waterproof cases could be greatly improved if more manufacturers incorporated two independent seals.

A limited number of trials were conducted with pyrotechnics, through prior arrangement with the Coastguard. The orange smoke from the Pains-Wessex Day/Night Distress Signal had a burn time of 20 seconds. It produced a smoke cloud that appeared dense at 4km and lingered for about 90sec. As the already considerable distance of the vessel was increased to 8.5km, the smoke remained visible for a similar duration. but appeared more diffuse and had a much lower profile. Wind speed on this occasion was less than 10mph.
A smoke flare was also used during a helicopter search in Shetland, when wind speed was more than 20mph. The smoke cloud was rapidly diffused.
It is unlikely that any observer would locate smoke unless they happened to be looking in roughly the right direction. Smoke would be best deployed by a diver who could see that a vessel or helicopter was heading towards him.
The same applies to the night flare on the Day/Night Distress Signal, which produced a dense cloud of white smoke that was visible in daylight at 8.5km, but was not located in darkness.
Miniflares had consistent burn times of 10sec and were faintly observed up to 8.5km away in daylight. In darkness they were easily located at more than 9km. As they come in packs of 10, they would be best deployed intermittently, keeping several back for when a search vessel or aircraft is sighted.
Cold hands hamper activation of these pyrotechnics and we werent convinced that they would be practical for a diver wearing gloves. We wouldnt recommend their use by divers under a wide range of typical diving operations.
They are not designed to be taken under water, are relatively expensive, and inconvenient to transport. Long-term reliability after repeated underwater exposure is unknown.

A series of aerial relocation exercises by an SAR helicopter in Orkney and Shetland failed to locate several devices. But seen from an altitude of 300m and then 75m were the Presto Dyechem Sea Marker Dye (3400m, 760m), the yellow flag (2500m, 1450m), the decompression bag (2300m, 1200m), and the paired red Polyform buoys (900m).
In a full-scale search exercise in the main body of Scapa Flow, co-ordinated by Pentland Coastguard at the end of our trial period, we tested a large number of devices. An area of 8 square nautical miles was searched by two lifeboats and an SAR helicopter. In just over two hours the lifeboats located all the devices within their designated sectors and some deployed in adjacent search areas.
The yellow flags provided the greatest location distances, similar to those we had found from our earlier observations.
The helicopter covered the search area in about an hour and located six out of 10 devices. The Sea-Streak Marker Dye was not located, its plume of dye being extremely diffuse. Recovery of the buoy to which it was attached required several minutes of searching at its GPS deployment position to locate it.
The Presto Dyechem dye had produced a very impressive slick from which the release remained consistent for around two hours, easily observed by helicopter. But dye generally is unsuitable as an aid for sea-level location and was never located by the search vessels.

It became clear during the trials that ability to relocate devices at or close to sea level varied considerably between observers. For some divers, skippers and boat crews, visual impairments could have a profound effect on that ability.
We also found that the ability of many observers to spot different devices in varying conditions improved with practice, the conclusion being that, ideally, look-outs on diver-support vessels should be competent at relocating devices. They should also know what it is they are looking out for, so information on the devices in use might be invaluable if SAR facilities are required.
Under adverse conditions, or where there is believed to be a higher risk of divers becoming separated from the cover boat, at least two people should remain on watch.
And if there is a high risk of divers becoming separated from the vessel, careful attention should be paid to how many divers are in the water at one time, and which location devices are carried.
The full report, Diver Emergency Surface Location Devices, can be viewed on www.jeanelaine.co.uk/diveraids/ contents.htm

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Delayed SMBs are by far the most common location device used by recreational divers, with the most popular colour red or orange - largely because most SMBs are made in these colours. Divers prefer self-inflating or self-sealing SMBs, as they dont expel air if allowed to fall over.

This was confirmed when we surveyed more than 80 UK sub-aqua clubs. The response was a little disappointing, but a general picture was revealed.

Flags, torches and whistles appeared frequently, with almost half of divers questioned using or having used folding flags. Red and orange were again the most common colour.

More than half of respondents carried two or more torches, with a small unit frequently used as a backup to a larger, lantern-style main torch. A similar proportion of divers regularly carried a strobe, usually attached to their BC. Whistles used were generally of the moulded plastic mouth variety and incorporated as a fixture on BCs. A few divers used air-powered sirens attached to their buoyancy devices. An equal number considered whistles to be next to useless in many circumstances.

When asked which colour stood out best, divers reckoned it was orange. Five per cent said they were colour blind.

  • Sub-Aqua Products 01703 612144
  • AP Valves 01326 561040
  • Bowstone 0161 442 0272
  • Pains-Wessex 01705 775044
  • Swanborough 01964 532202
  • Sea & Sea 01803 663012