What Is a Hyperbaric Chamber? Types, Pressure and What It's Like Inside
A hyperbaric chamber is a sealed, pressure-rated vessel that raises the air pressure around you above normal atmospheric pressure while you breathe oxygen. That pressure change is the whole point: it forces extra oxygen to dissolve directly into the liquid part of your blood, so oxygen can reach tissue without relying on red blood cells to carry it.
Everything else; the shape of the chamber, whether it seats one person or twelve, whether it is made of steel or coated fabric; is engineering around that single idea.
How a hyperbaric chamber actually works
At sea level you live at 1.0 ATA (one atmosphere absolute), breathing air that is about 21% oxygen. Oxygen enters your lungs, binds to haemoglobin in your red blood cells, and gets carried around the body. Haemoglobin is close to fully saturated in a healthy person, so simply breathing more oxygen at normal pressure adds surprisingly little.
Pressure changes that. Henry's law says the amount of a gas that dissolves into a liquid rises with the pressure of that gas above it. Raise the pressure inside the chamber, give the person high-concentration oxygen to breathe, and oxygen dissolves straight into blood plasma; the watery fluid your blood cells float in.
Plasma-borne oxygen behaves differently from the haemoglobin-bound kind. It does not need a red blood cell to deliver it, so it can diffuse into places where circulation is poor, swollen, or physically compressed. That is why the best-evidenced uses of hyperbaric medicine are all situations where tissue is starved of oxygen: crush injuries, non-healing wounds, radiation-damaged tissue, gas embolism.
The types of hyperbaric chamber
| Type | Holds | Typical pressure | Where you'll find it |
|---|---|---|---|
| Monoplace | One person | 1.3-3.0 ATA | Private clinics, some hospitals |
| Multiplace | 2-12+ people plus an attendant | Up to 6.0 ATA | NHS hyperbaric units, diving medicine centres |
| Soft / portable | One person | ~1.3 ATA | Home use, some wellness studios |
Monoplace chambers are the ones most people picture: a clear acrylic tube, one person lying inside, the whole chamber pressurised with oxygen or with air while you wear a mask. You can see out for the entire session and talk to staff through an intercom. This is the standard format in private practice.
Multiplace chambers are rooms rather than tubes. The room is pressurised with ordinary air and each person breathes oxygen through a mask or hood, which means a nurse or technician can be inside with you. Multiplace units handle the emergency end of hyperbaric medicine; decompression sickness in divers, carbon monoxide poisoning; because a clinician can treat you at pressure.
Soft-sided portable chambers are a different category and it is worth being blunt about it. They inflate to roughly 1.3 ATA, they are usually filled with air rather than high-concentration oxygen, and they are typically used at home without any medical screening. They are not a cheaper version of a clinical chamber; they are a lower-pressure device used in a fundamentally different way.
What a hyperbaric session is actually like
The honest answer is that it is uneventful, which is what you want from a medical procedure.
Before. You change into cotton clothing. Synthetic fabrics, hair products, oils and anything that could generate a spark are left outside; an oxygen-rich environment is a fire risk and chambers are run accordingly. You will have been screened beforehand for the conditions that make HBOT unsuitable.
Pressurisation (5-15 minutes). The pressure rises gradually. Your ears feel full, exactly like descending in an aircraft, and you equalise by swallowing, yawning or pinching your nose and gently blowing. The air inside warms noticeably as it compresses. This is the part people find unfamiliar, and it is also the part where nearly all HBOT side effects happen.
At pressure (60-90 minutes). Nothing to do. You breathe normally. People read, watch something, or sleep. In a monoplace chamber you are lying down and can see the room around you.
Depressurisation (5-15 minutes). Pressure comes back down slowly, the air cools, and your ears usually clear on their own.
A typical course is 10 to 40 sessions depending on why you are having it; hyperbaric oxygen is dose-dependent, and a single session is rarely the point.
Who a hyperbaric chamber is not suitable for
This matters more than any list of benefits, because it is the part that gets skipped.
- Untreated pneumothorax (collapsed lung); an absolute contraindication. Pressure changes can turn it into a life-threatening emergency.
- Certain lung conditions; severe COPD with CO₂ retention, large emphysematous bullae, and recent chest surgery all need specialist assessment.
- Recent ear or sinus surgery, or an active ear infection; you may be unable to equalise safely.
- Some chemotherapy agents (notably bleomycin, doxorubicin and cisplatin) interact with high-dose oxygen.
- Claustrophobia; usually manageable in a transparent monoplace chamber, but tell the clinic in advance rather than discovering it at pressure.
- Uncontrolled high fever, or pregnancy; both need individual clinical assessment before proceeding.
Any clinic that does not screen you against this list before your first session is skipping the step that makes hyperbaric medicine safe.
Where hyperbaric chambers are used in the UK
The NHS runs a small number of hyperbaric units, concentrated near the coast and in diving-medicine centres, and treats a defined list of conditions: decompression sickness, arterial gas embolism, carbon monoxide poisoning, certain non-healing wounds, and radiation injury to soft tissue and bone. If you have one of those, that is the correct route and it is funded.
For everything else; recovery support, training load, post-surgical healing, general wellbeing; the NHS does not provide hyperbaric oxygen, and private clinics are the practical route in the UK. The evidence base across those uses varies a great deal, from well-established to genuinely preliminary, and a clinic worth using will tell you which is which rather than presenting them as one undifferentiated list.
Hyperbaric chambers and iron: a connection worth knowing
Hyperbaric oxygen improves how much oxygen your plasma can carry. It does not fix the reason your red blood cells were not carrying enough in the first place.
If you are persistently tired, breathless on stairs, or foggy, one of the most common and most treatable explanations in the UK is iron deficiency; and it is diagnosed with a blood test, not a chamber. Iron deficiency is genuinely common, particularly in women with heavy periods, in pregnancy, and after surgery. It is worth ruling in or out before spending money on anything else, because if that is the problem, oxygen therapy is treating a symptom and leaving the cause in place.
Tired, foggy, or breathless on the stairs?
Before you go looking for oxygen, find out whether your body has enough iron to carry it. A ferritin blood test is the way to know.
Check your symptomsFree consultation · No referral · No waiting list
The short version
A hyperbaric chamber is a pressure vessel that lets you dissolve oxygen into your blood plasma. Clinical chambers run at 1.3-3.0 ATA, come as single-person tubes or multi-person rooms, and are safe when you are screened first and supervised throughout. Home units are a lower-pressure, unscreened category and should not be treated as equivalent.
If you are considering it for recovery or fatigue, the useful order is: find out what is actually causing the problem first, then decide what to do about it.
Related reading: What is hyperbaric oxygen therapy? · HBOT benefits: what the evidence actually shows · HBOT side effects and safety · Does the NHS offer hyperbaric oxygen therapy?
In Wales: Hyperbaric oxygen therapy in Cardiff · HBOT across Wales
Frequently asked questions
What is a hyperbaric chamber?
A hyperbaric chamber is a sealed, pressure-rated vessel that raises the air pressure around you to above normal atmospheric pressure while you breathe oxygen. The higher pressure dissolves extra oxygen directly into your blood plasma, so it can reach tissue independently of red blood cells. Chambers range from single-person clinical units to multi-person rooms in NHS hyperbaric units.
What pressure does a hyperbaric chamber use?
Clinical hyperbaric chambers typically run between 1.3 and 3.0 ATA (atmospheres absolute). Normal air pressure at sea level is 1.0 ATA. Wellness and recovery protocols usually sit at the lower end, around 1.3-2.0 ATA. NHS treatment for decompression sickness can go considerably higher.
What does it feel like inside a hyperbaric chamber?
Most people describe it as unremarkable. As the pressure rises you feel fullness in your ears, like an aeroplane descending, and you clear it by swallowing or yawning. The chamber warms slightly during pressurisation. After that you sit or lie still, and most people read, listen to something, or sleep.
Are hyperbaric chambers safe?
In a supervised clinical setting, yes. The most common side effect is temporary ear or sinus discomfort from the pressure change. Serious complications are rare when patients are screened beforehand and the session is supervised by trained staff. Screening matters: some lung conditions, recent ear surgery and certain medications make HBOT unsuitable.
Is a home hyperbaric chamber the same thing?
No. Soft-sided portable chambers sold for home use operate at much lower pressure; often around 1.3 ATA; and are not equivalent to a clinical chamber. They are also used without medical screening, which is the part that makes hyperbaric treatment safe. If you have a health condition, screening is not an optional extra.
Can I get hyperbaric oxygen therapy on the NHS?
The NHS provides hyperbaric oxygen therapy for a defined list of conditions; decompression sickness, carbon monoxide poisoning, certain non-healing wounds and radiation injury; through a small number of specialist units. It is not available on the NHS for recovery, fatigue or general wellbeing, which is why private clinics exist for those uses.