MEDICAL FAQs

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I think you need to use good old common sense here. Sure the manuals and tables show that at this height you would not precipitate a DCS. But we have all heard stories of driving over from Dahab to Sharm where the road takes you this height and it bringing on a bend.

It would be sensible to glide in the morning and dive after that. But I suppose there aren't any good warm thermals in the dawn of a day.

My gut feeling it do not risk it, but I am sure if you dove on Nitrox, to a reasonable depth and used air tables, then a glide to 2000ft would be OK a few hours later.

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Exploding bags of salad are a somewhat unusual diving hazard but I imagine you must have nearly rolled your vehicle with your windscreen suddenly being splattered with foliage. It’s a very good illustration of expanding gases and Boyle’s Law though. We at the Chamber have been considering this long and hard, and have done some digging around as it is a bit of an unusual one. However there don’t seem to be any specific tables or hard and fast recommendations for this scenario. In essence what you are doing here is the equivalent of flying after diving, and as such you really ought to be leaving a good 24 hours after your final dive before driving home. In naval rescue situations the usual ceiling on flying immediately after diving is 300m, so you are well in excess of this, and as such this is somewhat risky. The potential for bubble expansion precipitating a bend is well known even with moderate altitude increases. If you are going to be doing this regularly, then the best advice would be to stay at sea level for the duration of your dive trip and then leave 24 hours before driving home – maybe you can get to know your greengrocer and eat some salads fresh instead of bagged. If you really must go home each day then maximise your safety margins and minimise your nitrogen load, by eg. using Nitrox on air tables, leaving it as long as possible after diving before ascending, allowing regular no-diving days to allow yourself to off-gas, and keeping your depths and times well within the tables. I have to say I could not possibly recommend this course of action as it does pose a significant risk of getting bent – if you can afford it I would almost consider getting your own recompression chamber built in a bespoke annexe so that you can leap in as soon as you get home!

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A few basics first: the atmospheric pressure at sea level is defined as 1 atmosphere absolute (1 ATA). Aircraft cabins are usually pressurised to around 0.8 ATA (the equivalent of 7500 feet). This doesn’t sound much less, but it’s enough to allow bubbles to expand and start causing symptoms. If this happens, then you need to alert the cabin crew immediately, get yourself on oxygen, and stay as well hydrated as possible: basically the same steps as you would take with a bend in any other circumstance. Obviously there’ll be limited resources available for DCS treatment on a plane, so the sooner it descends the better. There is some limited evidence that tenoxicam, an anti-inflammatory drug, can reduce the number of recompression treatments required to achieve recovery, so if you happen to have any of these in your medical kit then there wouldn’t be any harm in taking 20mg. (To my knowledge there have been no big trials of other anti-inflammatories as yet.) Otherwise, it’s get thee to a chamber as soon as you land, and try to resist knocking back the Bloody Mary’s en route.

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Flying leads to numerous assaults on our usually jovial demeanour, turning us from polite, compliant citizens into rabid, slavering Visigoths. These arise as a result of the reduced air pressure and oxygen content in the cabin, the motion of the plane, the general stress of travelling and the major irritation of fellow passengers, who always seem to be enormous smelly social outcasts of dubious genetic stock who spill over into your seat and have bladders the size of dried peas. Add in a heady mix of dehydration, fatigue and immobility, together with a large splash of pre-holiday alcohol, and your recipe for a ragged, strung-out holidaymaker on arrival is complete. There’s no scientific reason that you should be more susceptible to a problem if you dive soon after a flight, but with these factors swirling about I’d always recommend a bit of a chill-out on touching down, so you’re in the right frame of mind for your first dive.

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I can’t imagine why you’d want to jump off a cliff and catch thermals immediately after a dive (there are many easier ways to dry off – a towel, maybe?) but each to their own I suppose. You are correct – from the point of view of DCS risk, this would be an eminently unsafe thing to do, for reasons already outlined. That said, there are occasions when people have no choice but to ascend to altitude, for example in military situations (as you’ve alluded to), or when no pressurised mode of air transport can be found. Far from being top secret, the US Navy guidelines are publically available – commendably full and open transparency from the same country that set up the First Earth Battalion and believed they could kill goats by staring at them. There are tables therein which enable you to calculate the surface interval required before flying, dependent on the planned increase in altitude and the highest repetitive group designator obtained in the previous 24 hours. If you absolutely must fly, the current generic recommendations are to do it “as low as safely possible, preferably less than 1000 feet”. Although I’ve never tried hang-gliding, I would imagine that it’s easily possible to exceed this altitude, and moreover find it very difficult to control the speed of ascent if you end up in a thermal. Might I suggest a slightly less provocative post-dive pastime – macramé perhaps, or beekeeping?

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One oft-overlooked precipitant of symptomatic bubble expansion is the trip home over the hills or a mountain range. For some reason such a land-based ascent is frequently neglected, but the pressure reduction can be similar to that of a flight and hence equally capable of bringing on a bend. When diving at altitude, adjustments do need to be made to compensate for the reduced atmospheric pressure – basically, more decompression is required than an identical dive at sea level. You can use specific altitude tables, or apply a cross-correction technique that rejigs the depth and stops to their sea level equivalents (see the trusty US Navy Diving Manual for specifics). Dives at altitudes of up to 300 feet are generally feasible without correction, but as altitude increases, progressively greater fudge factors are used. Another interesting facet that sometimes comes into play (and may have done in your case) is acclimatisation. If you dive within 12 hours of arriving at altitude, you will still have residual onboard nitrogen from your point of departure (assuming it was at sea level, or at least at a lower altitude), which needs to be factored in as well. In effect, the ascent to altitude is counted as a dive, and therefore you’ll start your first actual wet dive in a repetitive group. So there are a few modifications to familiarise yourself with, but nothing that a bit of time with a dive planner won’t clarify. I’m dying to know where your dives were now!

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I’ve recently joined the merry throng of lunatics that are ‘married men’, so thought it was about time we visited the Maldives. Hence this exact issue reared its head whilst we were contemplating our navels on a paradise beach in the Indian Ocean. I’d kept an eye on the altimeter in the cockpit on the way in, which seemed to register 3500- 4000ft during the transfer. Chatting to the pilot, it turns out they sometimes need to fly above or around thunderstorms, and hence can reach altitudes of 15000ft. And as you say, the cabins are not pressurised.

Now the US Navy Diving Manual states transfer of a DCS patient by air should be at 1 atmosphere if possible, ie. at sea level; if not, it should be by “unpressurised aircraft flown as low as safely possible (no more than 1,000 feet is preferable)”. So clearly they are concerned about the risk of bubble expansion at altitudes higher than this. To my mind, we therefore need to be conservative about the no-fly time after diving, and I would suggest a minimum of 24 hours, with the final days’ diving conservative (a single, shallow, no-stop dive if possible).

So even a single dive on day 6 might be pushing it. I’d advise an entire day off to off- gas fully; indulge yourself in ridiculously large meals and beach time, with some nocturnal Bacchanalian boozing thrown in. Having just done this, I can highly recommend salt and pepper squid served with chillies and copious quantities of chilled white – guaranteed to eradicate any gut bugs that might be trying to hitch a ride home with you.