Demystifying Recompression Chambers

Bret GilliamMany divers have seen a chamber either in photographs or in real life, but very few have ever had occasion to be in one unless they were being treated.  As a result a certain “mystique” has developed about chambers and many divers regard them as hostile and menacing environments.  Briefly, we would like to acquaint our readers with the realities of these important devices.

Generally, chambers are divided into two categories:

recompression chambers (used for the treatment of diving related injuries and other ailments) and  decompression chambers (used for surface or deck decompression facilities so the working diver can be removed from the water and complete the decompression obligation in a dry and controlled situation)

Both of these units are also properly referred to as “hyperbaric chambers”, meaning that the pressure inside will be higher than normal atmospheric pressure. These elevated pressures are usually expressed in feet of seawater (fsw) just as if we were diving in the ocean.  Air pressure is introduced to the chamber to raise its internal pressure and begin the “dive”.  We can then use these chambers to treat DCS (decompression sickness) or AGE (arterial gas embolism) cases, conduct “dry” surface decompression schedules, or simulate dives for research purposes.

In hospital situations, the role of hyperbaric medicine has been recognized as a specialty wherein victims of such injuries as crush wounds, burns, skin grafts, gangrene and carbon monoxide poisoning are treated with oxygen in large climate-controlled chambers.  These typically are able to accommodate as many as 18 patients at once, have hatches shaped and sized like conventional doors, are equipped with air conditioning and humidity controls and even piped-in music.

In the “field”, things are just a little bit different.  Forget the creature comforts and get prepared for close quarters.  Although a well set up field chamber can provide the same therapeutic benefits to a stricken diver, they are substantially smaller in most cases.

Field chambers range in size typically from 48 inches in diameter to 72 inches and are usually made of steel.  In the past, monoplace chambers were in common use in commercial diving theatres and were designed to pressurize one patient in a single cylinder.  This did not allow an inside tender to attend the patient and therefore he was pretty much on his own once treatment was initiated.  Rarely will these chambers be encountered today.  Most will be variations on the multi-place (more than one patient or tender) multi-lock (two or more pressure compartments with sealing hatches).  These allow several divers to be treated at once with an inside tender to monitor their condition.  Medical equipment or relief staff can be “locked” into or out of the chamber by use of the outer lock that can be pressurized to equal the treatment inner lock and subsequently depressurized to travel back to the surface pressure.

From the outside of the chamber, the supervisor can control the depth of the dive or treatment schedule and choose what gases will be supplied to the occupants.  Pressurization is accomplished with standard air but most modern treatments call for oxygen therapy beginning at 60 fsw (2.8 ATA).  Nitrox mixes of 50/50 (N2/O2) or 60/40 (N2/O2) are commonly used deeper than 60 fsw instead of air to lesson narcosis (and inert gas tissue loading) and safely keep the oxygen partial pressures within tolerance ranges.  Both oxygen and nitrox therapy gases are delivered to the patient or tender via BIBS (built-in-breathing-system) masks similar to aviator oxygen masks.

The chamber supervisor monitors his gauges that are calibrated to display pressure in fsw graduations.  He also has an oxygen analyzer plumbed into the chamber to monitor the inside environment’s O2 percentage.  Due to fire hazards, this percentage of O2 (referred to as the fraction of oxygen or FO2) inside the chamber will not be allowed to exceed 25%.  Most BIBS are set up with “overboard dumps” that exhaust the expired oxygen outside the chamber to prevent the rapid rise of the FO2.  However, it is common to have some leakage of masks due to improper fit etc. and O2 will be leaking into the chamber from this source.  As the supervisor sees the FO2 approach the 25% level he will institute a chamber “vent” where the inner lock is flushed with air by inputting pressure and simultaneously exhausting the incoming air from an outflow valve.  This scrubs the chamber of excess O2 and also cools and refreshes the atmosphere.

The supervisor is assisted by an outside operator and a record/time keeper who logs all stages of the treatment.  They can communicate with the inner occupants via a low voltage radio or sound-powered phone handset to discuss patient status or to confer on treatment procedures.

Inside the chamber, the patient will either lie in a supine position or sit up with the legs outstretched while leaning back against the chamber wall.  A fire-retardant mattress is usually provided or bunks may be hung from the chamber sides.  Medical equipment, or fluids etc. may be passed inside via a medical lock (small hatch door compartment usually about 12 inches in diameter) or through the same outer lock that accommodates staff transfers.

A patient is cleaned of all oils such as sun tan lotions or chap sticks and he is given fire-retardant clothing to wear.  This further reduces the chance of fire.


When a patient is presented to a chamber facility, the diver medical technician (DMT) or chamber supervisor will want to perform a gross physical and neurological examination to list the diver victim’s symptoms.  There is a protocol for rapid neurological exams that can be done in four minutes.  In severe cases, the exam will be done in the chamber if the patient’s condition precludes further delay.  The DMT will note the patient’s deficits and observe that many of them may fall in our symptom list.  However, that alone does not qualify our patient as a confirmed DCS case.

Confirmation or qualification of DCS is accomplished by a Test of Pressure.  The patient is recompressed to a depth of 60 fsw (2.8 ATA) and put on O2 via BIBS mask for a twenty-minute breathing period.  If pain, paralysis, weakness, or other symptoms are relieved or improved during this test of pressure breathing period it is presumed that DCS exists and is the source of the patient’s problems.  Similarly, if no relief is noted then DCS is typically not considered a factor in the patient’s ailment and further medical analysis takes place.

This distinction is important since divers can manifest symptoms that would be very similar to DCS from other problems including muscle strains from lifting gear or an idiosyncratic reaction to medication.  This test of pressure confirms whether further recompression therapy would benefit the patient.  Applying this test has proven to be nearly 100% reliable.

During the period of the test of pressure a determination will be made as to what the appropriate Treatment Table applies.  This is determined by the time factor involved for the relief of symptoms and the seriousness of symptom presentation.  Patients resolving in ten minutes or less have historically been treated on Table 5.  If resolution takes longer or if any Type II symptoms were initially presented, a Table 6 is chosen.  This is a judgement call and the current trend is more towards committing to a Table 6 regardless of time factor resolution.


As the chamber is pressurized with air, the occupants will immediately sense the pressure change in their ears and the equalization techniques will be necessary.  Usually the outside operator will observe through a signal from the inside tender that all occupants are clearing comfortably.  If problems occur and someone is slow to clear, descent is stopped until rectified.  Remember that our patient needs to get down to 60 fsw as quickly as possible to begin treatment so in many cases the dive is conducted as fast as the occupants can equalize.  In cases where severe DCS symptoms are present and the patient cannot clear, the eardrum may be punctured by the inside tender to allow the dive to continue (a ruptured ear drum will heal, DCS may not).

During the dive it gets quite noisy inside as air pressure is introduced and protective ear-muffs allowing equalization may be provided for occupants.  It also gets hot!  Compression of the air atmosphere rapidly raises the temperature inside the inner lock to nearly 100+ degrees F. in tropical locations. Newcomers will be surprised to notice the high-pitched speech caused by the increased air density. This becomes more pronounced and distracting as depth increases. In deep treatments, as in Table 6A at 165 fsw, speech, even between staff members, is discouraged if the chamber environment is air. The altered voice effects can stimulate narcosis in less experienced tenders or ones with less adaptive time at chamber depths.

Once reaching treatment depth the chamber will be aggressively vented to flush out the stale, hot, humid air and replace it with fresh.  The patient will be breathing O2 via BIBS mask in 20-minute intervals with five-minute “air breaks” where the mask is removed and chamber air is breathed.

Air breaks are provided for the patient’s comfort and to allow him recovery time from breathing pure oxygen for prolonged periods.  At any time during treatment if symptoms of chronic pulmonary (whole body) or CNS O2 toxicity are noted, the tender will suspend BIBS mask breathing and provide a 15-minute air break.  This time is not counted as part of the treatment table.  After this rest, the schedule is resumed on BIBS O2.  Standard treatment Table 5 is two hours and 15 minutes long and Table 6 is four hours and 45 minutes long.  Extensions may be added to Tables at the supervisor’s discretion.

Traditionally, Table 5 is reserved for the less serious, pain-only bends while Table 6 is used for more serious DCS involvement and pain-only bends that is not relieved in the first ten minutes of O2 breathing at 60 fsw.  Most chamber supervisors will now go directly to Table 6 in treating sport divers.  This is due to the fact that upon close neurological examination of patients it has been found that pain-only symptoms frequently masked or distracted from the more severe, but less compelling (in the patient’s mind), Type II symptoms of numbness and other CNS manifestations, etc.

The more immediate treatment is instituted, the better the chances of complete recovery.

During treatment, the ascent phases will be marked by the chamber dramatically cooling as the pressure is reduced.  In many instances, the air will become so humid that a dense mist is formed, almost like being in a cloud. The mist can be irritating to the throat if inhaled and cause coughing or choking so breathing is always done through the nose. If coughing etc. develops, the ascent will be stopped to avoid the hazard of embolism.

Training is available in chamber operations and medical support from several sources.  Some facilities offer seminars designed for sport divers to learn more about chambers and afford the opportunities to make actual chamber dives.  The Catalina (California) chamber sponsors such programs and back in 1988 I developed a certification program in Accident Management/Recompression Chambers that included patient handling and first aid, O2 administration, symptom recognition and two chamber dives.  Almost two thousand sport divers went through this training during that period aboard the 550-ft. 28,000 ton dive/cruise ship Ocean Spirit. One of the most popular technical chamber programs in the U.S. is offered by Dick Rutkowski’s Hyperbarics International in Key Largo, Florida.

With more chambers coming on line in popular diving destinations, it is far easier for divers to get local treatment and avoid the delay and considerable expense of air evacuation. Many facilities are privately operated and funded by contributions from local operations and visiting divers. It’s possible to arrange a tour of chamber facilities in many areas with just a phone call while on vacation. In some cases, a chamber dive can be accommodated for those with more than a passing interest. It’s a fascinating way to spend a few hours and most divers will find it beneficial educational experience.

And don’t forget to buy specific diver medical insurance like the policies available through DAN. Treatment isn’t cheap and air med-evac may be required just to get you from a remote location, resort, or liveaboard to the nearest chamber. It can easily run up a bill in the tens of thousands of dollars. Insurance is inexpensive, reliable, and you’ll sleep better knowing that your credit card or cash won’t be bottomed out if you surface with a shoulder pain that probably didn’t happen when you lifted your dive bag on to the boat that morning. Remember, as Jackson Browne said in his old song, “Nobody Rides For Free”. That’s advice you can take to the bank.

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7 thoughts on “Demystifying Recompression Chambers”

  1. My Orthopedic Surgeon was US Navy trained in Chamber operation.He told me of a DCS case that did not make it.
    This was a man who was Horribly Bent. He was not a US Navy Diver, but a local diver.Clearly, this Surgeon was very upset at this loss of life.
    This was tough to listen to, but an important tale for diver’s to hear.

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  2. Being inside a chamber that his baking in the tropical sun is not a good time. We used to take extraordinary steps to make those inside as comfortable as possible using massive ice packs, erecting temporary shade covers, and a continuous stream of cool ocean water over everything. We also added more frequent vents and plenty of fresh water to drink during the air breaks.

    We all prefer nice air conditioned facilities…


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  3. You haven’t lived until you’ve experienced a chamber deco ( after a 270′ surface gas jump ), in an un-shaded chamber, welded to the deck of a construction barge, under a broiling Indonesian sun! I survived such a deco by having the chamber operator run a slow, continuous vent ( though the incoming air was very hot, at least it was a “breeze!” ). The sweat poured out of me continuously & nausea was my constant companion – hyperthermia is no fun!

    Needless to say, I rigged shading over that chamber asap & plumbed up some piping to run continuous seawater over the chamber while someone was inside.

    I now have great empathy for boiled lobsters!


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  4. Googled PTZ camera – Pan, Tilt & Zoom Cameras….but I too wonder how it relates to this article… Thanks for the great detailed article Bret.

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  5. The best concise explsnation I have seen. I am fortunate to have experienced chamber “demo-dives” with my club in the chambers at St. Luke’s Hospital in Miwaukee, and in our basic course we try to organize a trip for each class. The students get a real eye-opener! Would it be OK for me to copy this article for distribution to the class? Maybe then more of them would pop for the $50 fee that the chanber requires.
    Randy Cooper

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  6. What the hell is a “Ptz camera” and how might such a device work in the treatment of divers?

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  7. Ptz cameras can often be useful in this eventuality

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