Free Diving Hazards

Sam Espinosa parked his battered pickup truck full of yellowfin grouper, snapper, and pay for essay writing a smattering of big pelagic fish in front of my office and with obvious difficulty climbed the front walk. He presented himself with progressive symptoms including limb pain, patchy areas of numbness and tingling, along with exceptional fatigue and severe headache. He told me that he and his brother had been spearfishing from early morning until just before sundown in depths up to 125 feet.

He noticed the pain symptoms around mid-afternoon, but attributed them to the rigors of his work wrestling large fish to the surface and continued his dive activities. Both men had clearly identifiable decompression sickness (DCS) symptomatology and I started them on demand valve 100% oxygen and aggressive fluids. Arrangements were made to evacuate them from St. Croix to a recompression  chamber off island.

By now you’re thinking “Big deal: deep repetitive dives with a heavy exertion component. Is there some surprise that they got bent?” Right on all counts, but these men were not scuba diving. They were professional commercial fishermen who did all their hunting by freediving… holding their breath. This was 1973 and I had never seen a case before of DCS purely from freediving. In fact, like most divers and chamber staff of that era, we had never even given much serious consideration to that possibility. As the local spearfishermen were to prove with uncanny regularity over the next few years, we were naive in our preliminary skepticism.

Both of these men recovered completely but they kindled my interest in free-diving induced DCS for professional and personal reasons. Most Virgin Islands’ health professionals had dismissed any physiological threat of DCS to breath hold divers as impossible and were more inclined to catalog such presentations as traditional muscle strains or carbon dioxide related brain phenomena.

During this same time in the early 1970s, I was involved with some of the best freedivers in the Caribbean who competed in spearfishing contests where depths could range from 60 feet over typical reef bottoms to hunting along the drop-off walls where the 150 foot levels would occasionally be reached. Following my experience with the Espinosa brothers, several of us experimented with wearing the old Scubapro/SOS decom meter during prolonged diving days with interesting results.

Many of us were able to advance the analog needle almost into the “red zone”, indicating required decompression. And our diving routine was far less demanding than the local “pros” who typically dove more frequently per hour and for longer bottom times at the deeper depth. Had we had the luxury of wrist mounted modern dive computers with their more conservative decompression models, we almost certainly would have incurred required stops or “ceilings” as the day progressed.

So can you get bent free-diving (breath hold diving)? Most divers would answer “no”. But there is no requirement that you breathe compressed air from a scuba tank to manifest DCS. The malady is dependent on time and depth primarily, and therefore expert breath hold divers can, in exceptional diving circumstances, place themselves within a window of vulnerability.

Competitive spearfishermen, South Pacific native working freedivers and Japanese Ama divers are most at risk. Typically, these divers can attain relatively deep depths (80 to 130 feet) for up to three minutes bottom time. Their profiles reflect an average to rapid descent followed by a “working” period at depth. Ascents are rapid, sometimes assisted by buoyant apparatus. Considerable exertion may be expended on the dive if the diver must struggle to land a large fish or to swim objects off the bottom. The new age of competitive free divers can go far deeper especially when clinging to descent sleds. And although their exertion levels are less, the intake of inert gas due to depth and subsequent rapid buoyant ascent pose unique risks for DCS.

Originally, little serious consideration was given to the prospects of freedivers falling victim to bends hits, but with Bob Croft’s dramatic dive to 240 feet in 1968 some discussions were prompted. Dives exceeding four minutes had already been recorded and anecdotal accounts of longer breath hold dives were in circulation. A 1962 National Geographic article recounts the diving style of a South Pacific diver: “A man from the Tuamotos who at 59 years old went to 100 feet as many as 50 times a day summed up his attitude toward this skill, ‘It is nothing… I have big lungs and a strong body. It is my work.’ Two minutes, three, four…a long time if you’re are holding your breath, but what if you are trying to follow a fish?”

Surprisingly, no correlation between deep breath hold dives and symptomatic DCS was made in many cases. In National Geographic’s 1980 book Exploring the Deep Frontier the authors relate, “Oxygen deprivation much longer (than four minutes)… can be damaging or fatal. In the Tuamotos, those who make successive, lengthy dives to great depths, risk a condition they call taravana, a sickness that includes vertigo, nausea, partial or complete paralysis, and unconsciousness.” Don’t these symptoms have something of familiar ring to them? A quick glance through any DCS symptom list should provide some easy match-ups.

Admittedly, it takes an exceptional diver to get bent holding his breath but it obviously does happen. Readers are cautioned about deep breath hold diving following aggressive scuba diving activities. Dive instructor Scott Valerga of Virgin Gorda had made repetitive scuba dives in 1978 while taking tourist divers on scuba tours. When he was unable to free his anchor following the last dive, he made several dives to 90 feet holding his breath to break out the anchor. Within minutes after getting back on board, he was symptomatic of DCS. His previous diving schedule was within the limits of the Navy tables but with little safety margin. He was treated in the St. Croix recompression chamber operated by NOAA’s HYDROLAB facility with full recovery.

Although it’s unlikely that the average diver is capable of placing himself at much risk with his free diving skills, the combination of aggressive repetitive scuba diving over several days in resort or liveaboard situations, in combination with breath hold dives below 60 feet, could spell trouble for those individuals capable of performing at this level. Forewarned is fore-armed…

While you can’t get in trouble with lung over-expansion injuries from breath hold diving (unless you were to take a breath from a compressed air source while already underwater from a diver’s regulator, Spare Air, etc.), we do have another serious hazard to consider that deals with the consequences of excessive hyperventilation and the relationships of oxygen and carbon dioxide.

Most divers are familiar with the basic characteristics of oxygen as it occurs in our atmosphere.  It is a colorless, odorless and tasteless gas found free in dry air at 23.15% by weight and 20.98% by volume.  For discussion purposes, we will consider its volume percentage to be 21%. At the surface we are naturally adapted to this partial pressure, expressed as PO2 at .21 atmospheres absolute (ATA).  This is considered the reference point for “normoxic” conditions.

It is important to be aware of certain ranges of tolerance in normal, healthy persons.  Most people can maintain proper blood oxygenation down to .16 ATA (16% oxygen in the mix at surface pressure) but dropping much below this will limit performance/endurance and unconsciousness will likely result approaching .1 ATA (10% oxygen at the surface).

The diver may recall the old reference to the “Ten and Ten Rule” wherein it is supposed that blackout will occur if the percentage of either oxygen or carbon dioxide (CO2) reaches 10% in the gas mixture.  This was particularly important to competitive free divers and spearfisherman while holding their breath and attaining depths in excess of 80 to 100 fsw. Many of these individuals could reach far deeper depths through applied disciplines of hyperventilation and adaptation in conjunction with techniques employed to precipitate the “diving reflex” to extend time underwater.

This practice, however, is a double-edged sword: as depth increased CO2 was produced by the body’s metabolism, and absent any other source the original “O2 storage” achieved by hyperventilation was depleted. To a certain degree, the inherent risk was counterbalanced by a corresponding rise in the percentage of carbon dioxide (PCO2) in the system since this gas is a metabolic waste product as oxygen is burned.

The relationship is important because high carbon dioxide is a major stimulus to breathe while low oxygen is not. As the diver held his breath, oxygen was consumed and carbon dioxide partial pressures elevated. Eventually a little voice generated by the CO2 whispered in your ear, “Hey buddy, I’ll continue to hurt you unless you get back to the surface and get a fresh breath, you idiot!”  Now the insidious danger occurs. As the diver ascended, both partial pressures of the gases dropped accordingly. His stimulus to breathe was reduced as his partial pressure of carbon dioxide dropped… while his oxygen partial pressure could be dropping to dangerous levels simultaneously.

At some point, the diver passed out from this “latent hypoxia” syndrome or what became commonly known as “shallow water black out”. Typically the diver showed no signs or distress and simply went limp, sometimes within ten feet of the surface. Those who were successfully rescued and revived related no warning of the impending blackout or any major stimulus to breathe. But several fatalities were sustained before the problems were identified and the hazards of deep breath-hold diving were well communicated.

The recreational snorkeler puttering around enjoying the sights on a shallow reef can still sleep soundly. But as the popularity of freediving and more advanced applications such as spearfishing or competition attracts more divers to this purest form of underwater exploration, an awareness of these potential hazards is necessary.

Just when you thought it was safe to go back in the water…

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Author Notes: Bret Gilliam is a 43-year veteran of the professional diving industry and an ex-member of the Virgin Islands’ 1974 World Championship Spearfishing Team where he won individual honors for largest fish (taken free-diving in 125 foot depths).