When an SAQ asks what happens once a diver reaches the chamber, don’t stop at 100% oxygen at 2.8 ATA. When recompression is indicated for decompression sickness (DCS) or arterial gas embolism (AGE), a standard profile to know is U.S. Navy Treatment Table 6 (TT6), or a center’s selected equivalent. It compresses to 60 fsw, uses timed oxygen periods and air breaks, ascends to 30 fsw, then returns to the surface on a controlled schedule. The unextended table takes 285 minutes—4 hours 45 minutes—after arrival at 60 fsw; compression time is additional.
Start with the pressure, then name the table
TT6 is commonly used for DCS and AGE. The treatment pressure is 60 feet of seawater (fsw), about 18 m or 2.8 atmospheres absolute (ATA). “Absolute” means total ambient pressure, including the pressure at the surface; it is not 2.8 atmospheres added on top of surface pressure. In a chamber, 60 fsw describes an equivalent pressure, not a literal underwater depth.
The schedule then steps to 30 fsw—about 9 m or 1.9 ATA—before a slow return to surface pressure. Saying “60 feet, then oxygen” names the starting point, but misses the timed breathing periods and staged ascent that make this a treatment table.
| Phase | Standard TT6 schedule | Why it matters |
|---|---|---|
| Compress to 60 fsw | Navy manual descent rate: 20 ft/min. Begin treatment oxygen time on arrival at 60 fsw. | Recompression reduces bubble volume as ambient pressure rises. |
| At 60 fsw | Three 20-minute oxygen periods, each followed by a 5-minute air period (75 minutes total at 60 fsw). | Delivers oxygen at the highest treatment pressure while interrupting exposure to reduce the risk of oxygen toxicity. |
| Ascend to 30 fsw | 30 minutes, at no more than 1 ft/min; breathe oxygen. | Allows pressure to fall gradually while treatment continues. |
| At 30 fsw | 15 minutes breathing air, then 60 minutes oxygen, 15 minutes air, and 60 minutes oxygen. | Continues oxygen treatment at a lower pressure. |
| Ascend to surface | 30 minutes, at no more than 1 ft/min; breathe oxygen. | Completes the prescribed staged decompression. |
Those timed phases add to 285 minutes. The initial compression is not included; the planned ascents between treatment depths are. A chamber’s implementation may differ, so the hyperbaric team’s active table—not a memorized diagram—governs treatment.
Why oxygen is interrupted—and why ascent is slow
Pressure and oxygen do related but distinct work. Rising ambient pressure compresses gas bubbles; breathing oxygen also lowers nitrogen in the lungs, supporting movement of inert gas from tissues and bubbles into the blood and then out through the lungs. Oxygen can improve oxygen delivery to tissues affected by impaired circulation.
At 60 fsw, breathing pure oxygen means exposure to a high oxygen partial pressure. Air breaks interrupt that exposure to reduce the risk of central nervous system oxygen toxicity; they are a planned safety feature, not a sign that oxygen has stopped helping. The staged ascent matters too: lowering pressure too quickly can encourage bubbles to expand, whereas a controlled ascent gives dissolved gas time to clear.
What “4 hours 45 minutes” does—and doesn’t—mean
That number describes the unextended TT6 schedule, not a guaranteed total time from hospital arrival to chamber exit. It excludes compression to 60 fsw, and it does not include extra treatment time if the table is extended. Transport, stabilization, chamber preparation, and post-treatment observation are separate.
The table also is not automatically lengthened for every patient. Navy TT6 allows up to two additional 25-minute cycles at 60 fsw (20 minutes oxygen and 5 minutes air) and up to two additional 75-minute cycles at 30 fsw (15 minutes air and 60 minutes oxygen). Whether to extend depends on the patient’s symptoms and repeated clinical or neurologic examinations, with the decision made by the hyperbaric or dive-medicine team.
TT6A is not another name for TT6. In the U.S. Navy manual, TT6A is a different, deeper profile considered when severe symptoms remain unchanged or worsen within the first 20 minutes at 60 fsw. It is not a routine ED choice: decisions to change tables or treatment depth belong with clinicians experienced in diving medicine and hyperbaric care.
For the emergency team, the useful handoff is more than “suspected DCS.” Keep high-concentration surface oxygen going during the transfer when feasible, and send the dive profile, symptom onset and progression, treatment already given, and serial examination findings. The chamber team uses that clinical trajectory—not the diagnosis label alone—to guide the table and any modification.
Practical takeaways
- Name the table: When recompression is indicated for DCS or AGE, U.S. Navy TT6—or an equivalent center protocol—is a standard profile to recognize.
- State the depth correctly: 60 fsw is about 18 m and 2.8 ATA absolute; the next main treatment level is 30 fsw, about 1.9 ATA.
- Remember the pattern: timed oxygen periods with air breaks, followed by a slow staged ascent—not continuous oxygen at one pressure.
- Qualify the duration: 285 minutes (4 hours 45 minutes) is the unextended schedule after arrival at 60 fsw; compression and any extensions add time.
- Leave table changes to the hyperbaric team: symptoms and serial examinations guide extensions or a different protocol.
