1.5 ATA (1.5 times normal atmospheric pressure) is the chamber pressure used for every Hyperbaric Oxygen Therapy (HBOT) session at ReviveO2 in Littlehampton. This guide explains in plain terms what the number means, what you actually feel during a session, and why the pressure matters.

At a glance

  • ATA meaning: a unit for measuring pressure
  • 1.0 ATA: normal air pressure around you right now
  • 1.5 ATA: one and a half times normal - what ReviveO2 uses
  • What you notice: gentle ear fullness during pressure change, like flying
  • Session length: 65 minutes total (60 minutes at pressure)
  • Location: Bizspace, Courtwick Lane, Office 46, Littlehampton BN17 7TL
  • Parking: on-site plus on-street nearby
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Wellness note: HBOT at ReviveO2 is a supervised wellness session, not a medical treatment. It is not intended to diagnose, treat, cure, or prevent any disease. If you have a health condition or are unsure, check with your GP before booking.

What does ATA mean?

ATA stands for Atmospheres Absolute. It is simply a unit for measuring pressure, the same way kilometres measure distance or kilograms measure weight.

1.0 ATA is the normal air pressure you are sitting in right now. It is the baseline. 1.5 ATA is one and a half times that pressure: a moderate, controlled increase. Not extreme. Not uncomfortable. A gentle step up that does something specific and measurable to how your body absorbs oxygen.

According to the Undersea and Hyperbaric Medical Society (UHMS), increased atmospheric pressure causes a higher concentration of oxygen to dissolve directly into blood plasma. At 1.5 ATA the increased pressure forces oxygen to dissolve into the liquid part of your blood, reaching tissue that red blood cells alone cannot access. The mechanism is governed by Henry's Law (1803), the physics principle stating that gases dissolve into liquids in proportion to the pressure applied, first documented by William Henry.

Henry's Law - why 1.5 ATA matters

Henry's Law states that gases dissolve into liquids in proportion to the pressure applied. At 1.5 ATA (one and a half times normal atmospheric pressure), oxygen dissolves into your blood plasma in quantities not possible at normal pressure. That dissolved oxygen floats freely through the plasma, reaching tissue that red blood cells - which carry oxygen under normal conditions - cannot reach. Inside those cells, the extra oxygen supports the mitochondria, the tiny structures that produce energy.

Interactive - where does 1.5 ATA sit on the pressure scale?
1.5 ATA
1.5 ATA is ReviveO2's session pressure - one and a half times normal. Equivalent to being 5 metres underwater, but in a comfortable chamber. Meaningful oxygen dissolves into plasma. Calm and supervised.
1.0
1.1
1.2
1.3
1.4
1.5
2.0
2.5
3.0
Normal (sea level) Wellness HBOT Medical HBOT
1.0 ATA
Normal life
Where you are right now. Standard air pressure at sea level.
1.5 ATA
ReviveO2 sessions
One and a half times normal. Similar to 5 metres underwater - in a comfortable chamber.
2.0 ATA
Medical HBOT (low)
Clinical settings. NHS-approved conditions. Physician supervised.
3.0 ATA
Medical HBOT (high)
Decompression sickness, CO poisoning. Hospital only.
ATA = Atmospheres Absolute. Each 0.1 ATA increase is roughly equivalent to descending 1 metre underwater. At 1.5 ATA your body experiences conditions similar to being 5 metres below the surface - enough to dissolve meaningful oxygen into plasma, well within the comfortable wellness range.

Drag the slider to explore the full pressure range - from normal everyday air to maximum medical HBOT. ReviveO2 sits in the wellness zone at 1.5 ATA.

What does 1.5 ATA feel like?

Most people describe it like descending in a plane or driving up a hill quickly. Your ears feel a gentle fullness. A swallow or yawn clears it - the same movement that opens the small channel connecting your ear to the back of your throat, called the Eustachian tube. That equalising sensation is the main thing most people notice.

The pressure itself is not something you feel on your body in the way you might imagine: no squeezing or weight. The air around you changes, gradually and gently. Most people are surprised by how calm it feels once the pressure has stabilised.

We slow the pressurisation if you need a moment to equalise. We pause and wait if it takes longer. Comfort comes first, and Matt is with you throughout.

Interactive - what 1.5 ATA does inside your blood
1.5 ATA Wellness HBOT
At 1.5 ATA - ReviveO2 sessions run here. Oxygen dissolves freely into the plasma. Tissue cells beyond the vessel are now receiving it. The green glow shows oxygen arriving where red cells cannot go.
4.5 ml/100ml
Dissolved O2 in plasma
1.5x
More than normal
Extended
Tissue oxygen reach
Without HBOT - 1.0 ATA
With HBOT at 1.5 ATA
Red blood cell
Dissolved O2 (free in plasma)
Blood plasma
Tissue cell

Drag both sliders together to see how pressure and oxygen relate. At 1.5 ATA, dissolved O2 dots appear freely in the plasma and tissue cells glow green as they receive oxygen. Source: Henry, W. (1803). Philosophical Transactions of the Royal Society, 93.

Why the number matters for your session

For most people coming for the first time, the pressure number matters for two reasons: comfort and consistency.

Comfort, because knowing what 1.5 ATA means helps you understand the ear sensation before it happens. It is not alarming once you know it is coming and why.

Consistency, because 1.5 ATA is what ReviveO2 uses for every session. You are not guessing what pressure you will get. The chamber, the protocol, and the supervision are the same each time. The benefit of HBOT compounds across repeated sessions: dissolved-oxygen exposure accumulates as the routine builds, not from a single visit. For session frequency guidance, see the HBOT complete guide for Littlehampton.

The number also lets you compare HBOT offerings clearly. UK wellness centres operate at 3 main pressure levels, including 1.3 ATA at the lower end, 1.5 ATA at the standard wellness pressure, and 2.0 ATA and above for medical-grade settings. 1.5 ATA is a meaningful wellness pressure: high enough to dissolve oxygen into plasma, low enough to remain within supervised wellness without clinical oversight.

Before your session

Rescheduling is usually more comfortable when you feel blocked up, have ear pain, or have a heavy cold on the day. The Eustachian tube needs to open freely for the pressure change to feel easy, and congestion makes equalising harder.

Check with your GP before booking if you have any health concerns, including recent ear or lung issues, pregnancy, recent surgery, or medication questions. Every client completes a safety screening form sent by email before their first visit, so everything is checked before you arrive, not when you get there.

ReviveO2 is based at Bizspace, Courtwick Lane, Littlehampton (BN17 7TL), with on-site parking and easy access from Worthing, Rustington, East Preston, Arundel, Bognor Regis, and Chichester. The waiting area is calm and unhurried so you can settle before your session starts.

For full details on who should not use HBOT, see the HBOT contraindications guide.

How long is a session?

Your visit is about 65 minutes total: 60 minutes in the chamber at 1.5 ATA, plus 5 minutes for the gradual pressure change at the start and end. We adjust if you need more time to equalise. Nobody rushes.

Intro session at ReviveO2, Littlehampton. Safety screening sent by email before you arrive. No referral needed.

Book your first session

Frequently asked questions

ATA stands for Atmospheres Absolute. It is a unit for measuring pressure. 1.0 ATA is normal air pressure at sea level. 1.5 ATA means one and a half times that pressure - which is what ReviveO2 uses for every wellness HBOT session.
No. Medical HBOT is delivered at 2.0-3.0 ATA in clinical settings for specific NHS-approved conditions, under physician supervision. ReviveO2 operates at 1.5 ATA as a supervised wellness session - not a medical treatment, and no referral is needed.
Most people notice the pressure mainly during the gradual change at the start and end of the session. Once you are settled at 1.5 ATA, most people find it very calm; clients commonly read or rest. The pressure itself does not feel like squeezing or weight.
Tell us before you start. We can slow the pressure change right down or pause completely. Stopping and rescheduling is fine if it is not comfortable. For ongoing ear issues, check with your GP before booking.
Rescheduling is usually better. When you are congested, the Eustachian tube cannot open freely, which makes ear equalising harder and less comfortable. Rebook when you are clear.
Not usually. Most people go straight back to their day. We recommend drinking water and taking 5 minutes in the waiting area before heading out. Most clients feel refreshed or relaxed, and a small number notice nothing different at all, which is also normal.
1.5 ATA is within the wellness pressure range and is considered very safe for most people. Every client completes a safety screening form before their first session. Check with your GP before booking if you have any health concerns.
HBOT complete guide for Littlehampton → What to expect at your first HBOT session → Ear equalising tips for HBOT beginners → HBOT and claustrophobia: what the chamber feels like → Who should not do HBOT (contraindications) → How many HBOT sessions do you need? → HBOT pricing and packages → Nervous System Reset (NSR) at ReviveO2 →

Questions before booking? See the full FAQ or book your intro session online.

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References

  1. Henry, W. (1803). Experiments on the quantity of gases absorbed by water. Philosophical Transactions of the Royal Society, 93, 29-274.
  2. Tibbles, P.M. & Edelsberg, J.S. (1996). Hyperbaric-oxygen therapy. New England Journal of Medicine, 334(25), 1642-1648.
  3. Undersea and Hyperbaric Medical Society. uhms.org
  4. NHS. Hyperbaric oxygen treatment. nhs.uk
  5. National Library of Medicine. (2023). Hyperbaric oxygen therapy. ncbi.nlm.nih.gov
  6. DDRC Healthcare. ddrc.org
This article is for informational purposes only and does not constitute medical advice. Wellness HBOT at ReviveO2 is not intended to diagnose, treat, cure, or prevent any disease. If you have a health condition, consult your GP before booking.
M
Matt
Founder, ReviveO2 Littlehampton

Matt is the founder of ReviveO2, a wellness centre in Littlehampton, West Sussex. He supports visitors through check-in and session flow, with a focus on clear guidance, comfort, and safety. Matt completed hyperbaric chamber operator training in 2025 with DDRC Healthcare (Diving Diseases Research Centre, Plymouth), including the Chamber Operator course, focused on safe chamber operations and session procedures.