The question "how long is an HBOT session?" has no single answer. The honest answer: 60 or 90 minutes at therapeutic pressure, plus 10 to 20 minutes of compression and decompression.
The exact protocol depends on the indication.
This guide breaks down where each duration came from. It cites the original UHMS indications manual and the clinical-pharmacology research that set those numbers.
A note on language. Clinicians and clinics use "session length" inconsistently. A "90-minute session" at a hospital wound-care center means 90 minutes of treatment gas at 2.0 to 2.4 ATA. A "90-minute session" at a wellness clinic might mean 60 minutes of compressed time at 1.3 ATA plus 30 minutes of intake and exit.
We will be explicit about what each number measures.
The compression-treatment-decompression cycle
Every HBOT session has three phases. Compression brings the chamber from sea level to therapeutic pressure.
Treatment holds the patient at therapeutic pressure on 100% oxygen. Decompression returns the chamber to sea level.
Compression takes 10 to 15 minutes for a hard-shell monoplace at 2.0 to 2.4 ATA. Faster than that risks ear barotrauma. Slower wastes chamber time.
The treatment phase at depth is what the clinical literature counts. A "60-minute protocol" means 60 minutes at full therapeutic pressure. The compression and decompression do not count.
Decompression takes 10 to 15 minutes. Faster risks decompression sickness (in multiplace chambers with chamber attendants) and ear injury. Sechrist's operator manual for the Model 3300 specifies 5-15 minute compression and decompression rates. See the decompression sickness evidence atlas for the full study-by-study evidence breakdown.
Total clock time at a hospital wound-care center for a 90-minute treatment runs 110 to 120 minutes. Patients should expect to be on-site for closer to 2.5 hours including check-in and check-out.
The 90-minute UHMS standard
The 90-minute treatment block at 2.0 to 2.4 ATA is the dominant protocol for FDA-approved indications. It came out of the UHMS Committee on Indications consensus work in the 1980s.
The rationale is pharmacological. At 2.0 to 2.4 ATA on 100% oxygen, arterial PO2 rises from ~100 mmHg at sea level to ~1500 mmHg (Tibbles & Edelsberg 1996). Most cellular responses to hyperoxia plateau within 60 to 120 minutes.
Pushing beyond 120 minutes risks pulmonary oxygen toxicity. The Unit Pulmonary Toxic Dose (UPTD) curve quantifies the risk. A 90-minute session at 2.4 ATA delivers roughly 600 UPTD, near the daily-safe maximum.
The diabetic foot ulcer trials that established Medicare coverage used 90-minute protocols. Faglia et al. 1996 ran 90 minutes at 2.5 ATA. Abidia et al. 2003 ran 90 minutes at 2.4 ATA.
The radiation tissue injury research that supported CMS LCD coverage also used 90-minute protocols. The Marx & Johnson mandibular radionecrosis protocol uses 90 minutes at 2.4 ATA. That study set the standard for radiation indications.
The 60-minute variant
Some indications use 60-minute treatment blocks. The most common reasons are pediatric patients, high-risk adults, and chambers that cap at lower pressure.
Pediatric protocols often shorten treatment time to reduce barotrauma risk. Children have smaller eustachian tubes and tolerate slower equalization. A 2018 pediatric HBOT review summarized common pediatric protocols at 60 minutes at 2.0 ATA.
Adults with pulmonary risk factors — COPD, recent smoking, prior radiation to the chest — get shortened protocols to reduce oxygen toxicity. A clinician may step down a 90-minute protocol to 60 minutes at 2.0 ATA after a UPTD calculation.
Wellness clinics running 1.3 ATA soft-shell chambers default to 60 minutes total. At 1.3 ATA, oxygen-toxicity risk is much lower because alveolar PO2 is roughly 200 mmHg (vs ~1500 at 2.4 ATA). Duration is more of a scheduling decision than a clinical one.
Why duration is set by indication
Most patients want to know "how many minutes." The clinical answer is "depends on what we are treating."
The UHMS 14th Edition Indications Manual (2019) lists protocol depths and durations by condition. These are not suggestions — they are the protocols that produced the supporting evidence.
Air embolism uses US Navy Treatment Table 6: 2.8 ATA for 285 minutes total, with multiple air breaks. That is closer to 5 hours than 90 minutes. The protocol is specific to the indication. See the arterial gas embolism evidence atlas for the full study-by-study evidence breakdown.
Carbon monoxide poisoning uses a single 90-minute session at 2.5 to 3.0 ATA, often repeated at 6, 12, and 24 hours. The Weaver et al. 2002 trial that established the protocol used this exact schedule.
Diabetic foot ulcer uses 90 minutes at 2.0 to 2.5 ATA, 5 days per week, for 30 to 40 sessions total. Radiation soft-tissue injury uses 90 minutes at 2.0 to 2.4 ATA for 30 to 60 sessions.
Off-label uses do not have a UHMS protocol. Wellness clinics often pick durations based on chamber capacity and patient throughput, not on the underlying physiology.
What changes when you double the time
Sitting in a chamber twice as long does not double the clinical effect. The pharmacokinetics flatten.
Arterial oxygen plateaus within 5 to 10 minutes at depth. The relevant therapeutic effects — neovascularization, white-cell mobilization, hyperoxia-driven cellular signaling — happen over 30 to 90 minutes of sustained exposure. Beyond 120 minutes the marginal benefit drops sharply.
What does change is oxygen-toxicity risk. The lung is the first organ affected, and pulmonary oxygen toxicity develops over cumulative exposure.
A 180-minute session at 2.4 ATA delivers roughly 1200 UPTD, exceeding the recommended daily cap.
The central nervous system is the second risk organ. CNS oxygen toxicity (seizures) is rare at 2.0 ATA but rises sharply above 2.8 ATA. The Navy treats it with air breaks at depth.
So longer is not better. The 90-minute treatment block is a Goldilocks number. It maximizes therapeutic exposure while staying inside the toxicity envelope.
Air breaks at depth
A subtle but important detail. Most hospital HBOT protocols include 5-minute "air breaks" at depth. The patient breathes chamber air (or normoxic gas mix) instead of 100% oxygen for 5 minutes, then resumes oxygen.
The breaks reset the oxygen-toxicity clock without losing the pressure effect. A 90-minute treatment with two 5-minute air breaks delivers 80 minutes of hyperoxia at depth. The UPTD load drops accordingly.
Air breaks are standard in hospital protocols at 2.4 ATA. They are less common at 2.0 ATA because the toxicity risk is lower. Wellness chambers at 1.3 ATA do not need air breaks because oxygen-toxicity risk is negligible at that pressure.
If a clinic runs 90-minute sessions at 2.4 ATA without air breaks, ask why. The standard protocol includes them.
The "60 minutes is enough" wellness argument
Some wellness clinics argue that 60 minutes at 1.3 ATA produces equivalent benefit to 90 minutes at 2.4 ATA. The argument cites lower-pressure research from the Sagol Center and others.
The argument has a problem. Arterial PO2 at 1.3 ATA on 100% oxygen is roughly 600 mmHg, versus 1500 at 2.4 ATA. The 1.3 ATA condition delivers about one-third the oxygen dose (Tibbles & Edelsberg 1996).
"Dose equivalence" between 60 minutes at 1.3 ATA and 90 minutes at 2.4 ATA is not supported by the pharmacokinetics. Some downstream effects (gene expression, growth-factor release) may still occur at lower pressures, but the magnitude is unclear.
Our comparison of mild vs medical HBOT unpacks the dose-equivalence question in more detail.
The Aviv Clinics protocol uses 90-minute sessions at 2.0 ATA with intermittent 100% oxygen breaks. That is a clinical protocol, not a wellness one. We covered the marketing-vs-evidence gap in our Aviv evidence analysis.
Practical session-length reality at clinics
What this looks like in practice depends on the clinic type. We will lay out the three patterns.
At a hospital wound-care center: check in around 7:00 AM and in the chamber by 7:20. Compression to 2.4 ATA takes 12 minutes, then 90 minutes of treatment with two 5-minute air breaks. Decompression takes another 12 minutes, so you are out the door around 9:30.
At an independent hard-shell clinic: similar to hospital flow but more flexible scheduling. Total chamber time runs 110 to 120 minutes, and total visit time is 2 to 2.5 hours.
At a soft-shell wellness clinic: brief intake, then into the chamber at 1.3 ATA. Compression takes 3 to 5 minutes, treatment is 60 minutes, decompression is another 3 to 5 minutes. Total visit time is about 90 minutes.
The hospital protocol is more demanding because the indication is more demanding. Treating a diabetic ulcer is not equivalent to a wellness session. The protocols reflect the different goals.
Frequency and total session count
Duration of a single session is only half the picture. Total exposure depends on session count and frequency.
The 40-session protocol is the de facto standard for wound-care and radiation indications. That comes out to 40 × 90 minutes = 3,600 minutes of treatment gas across roughly 8 weeks.
Frequency is usually 5 days per week (Monday through Friday). Weekend gaps allow recovery from oxygen toxicity. Twice-daily ("BID") protocols exist for severe necrotizing infections but are not routine.
Wellness clinics often run 3 sessions per week for 12 to 20 weeks. That is a different total dose. It is also a different protocol from the clinical one.
Manufacturer guidance vs clinical guidance
Chamber manufacturers publish operating ranges. Clinical organizations publish treatment protocols. These are different documents.
Sechrist's operator manual for the Model 3300E allows pressurization up to 3.0 ATA. The UHMS protocol for diabetic foot ulcers caps at 2.5 ATA. The manufacturer says what the chamber can do; UHMS says what is clinically indicated.
The same applies to duration. A monoplace chamber can run a 4-hour session, but clinical protocols for routine indications never call for that.
The manufacturer permission and the clinical indication are different questions.
If a clinic argues "the manufacturer says 4 hours is fine," ask what indication justifies that duration. Then look up the indication in the UHMS Indications Manual. Usually the manufacturer-permission argument is being used to justify off-label scheduling.
What patients should ask
A short list of questions for any HBOT clinic about session duration.
What pressure is the treatment phase, and how long does it last? Compare against the UHMS indication for your condition.
Are there air breaks at depth? For 90-minute sessions at 2.4 ATA, expect yes.
What is the total clock time per visit? Plan for 2 to 2.5 hours at hospital clinics, 90 minutes at soft-shell wellness clinics.
How many sessions total are recommended? Standard wound-care is 30 to 40. Anything dramatically more is either a different protocol or a different sales pitch.
What does Medicare or insurance authorize for my indication? If the answer is "this is private-pay only," you are looking at off-label use.
For more on chamber-verification questions, read our guide to verifying a chamber is medical-grade.
Bottom line
The 60-minute and 90-minute protocols both exist because clinical indications and chamber types differ. There is no universally correct duration.
For FDA-approved indications, the UHMS Indications Manual is the authoritative source. For off-label uses, the protocol is whatever the clinic decided.
A 90-minute session at 2.4 ATA in a hard-shell hospital chamber is a clinical intervention with decades of pharmacokinetic research behind it. A 60-minute session at 1.3 ATA in a soft-shell wellness chamber is a wellness experience whose physiological dose is roughly one-third.
Both can be appropriate. Neither is a substitute for the other.
Related Reading
- The 40-session HBOT protocol explained
- Mild HBOT vs medical HBOT: why 1.3 ATA is controversial
- How to verify a clinic's chamber is medical-grade
- Aviv Clinics: evidence vs marketing
- FDA-cleared hyperbaric chambers complete list
Frequently asked questions
How long is a typical HBOT session?
For FDA-approved indications, 90 minutes at treatment pressure plus 20 to 30 minutes for compression and decompression. Total clock time is roughly 2 hours.
Why are some sessions 60 minutes instead of 90?
Pediatric protocols, patients with pulmonary risk factors, and soft-shell wellness chambers all default to 60 minutes. The clinical reason is reduced oxygen-toxicity exposure.
Are longer sessions more effective?
Not really. Therapeutic effects plateau at 60 to 120 minutes of hyperoxia, while toxicity risk rises with duration. The 90-minute block is the established balance.
What are "air breaks" during a session?
5-minute intervals at depth when the patient breathes chamber air or normoxic gas instead of 100% oxygen. They reduce cumulative oxygen-toxicity exposure without losing the pressure effect.
How many total sessions are typical?
The de facto standard for wound-care and radiation indications is 30 to 40 sessions over 6 to 8 weeks. Anti-aging and off-label protocols can run 60 or more, but those are not the clinical norm.
Medical disclaimer: This guide is informational and does not constitute medical advice. HBOT carries real risks including ear barotrauma, oxygen toxicity, and chamber fire. Discuss any HBOT plan with a physician trained in undersea and hyperbaric medicine before starting. The FDA has cleared HBOT for 13 specific indications; uses outside those indications are off-label and not supported by FDA evaluation.
-- The HBOT Finder Team