Brian Andrew Hills and Decompression Theory

By Rubicon Foundation editorial team

5 min read · 1 November 2026

Brian Andrew Hills is associated with the development of decompression theory: the effort to explain how pressure changes and inert gases affect the body during and after a dive. This subject matters because safe ascent depends not only on depth, but on how gases move between breathing gas, blood and tissues.

Why does decompression depend on tissue gas?

At depth, the increased ambient pressure raises the partial pressure of inert gas in the breathing mixture. Nitrogen, or another inert gas used in a breathing mixture, then enters the body’s tissues. The amount absorbed depends on exposure time, pressure and how readily each tissue takes up and releases gas.

During ascent, falling pressure reverses the gradient: inert gas leaves tissues and is carried to the lungs for elimination. If pressure falls faster than the body can manage, bubbles may form or grow. Their effects range from local tissue disturbance to problems involving circulation or the nervous system.

Decompression theory therefore has to describe both gas exchange and the limits of safe pressure reduction. It is a model of a complex biological process, not a direct measurement of every tissue in a diver’s body.

What is the central problem in decompression modelling?

A decompression model estimates how inert gas behaves across a dive and translates that estimate into ascent procedures. Different tissues exchange gas at different rates, so a single compartment cannot represent the entire body. Models use theoretical compartments to approximate this range of uptake and elimination.

One enduring challenge is that dissolved gas and bubbles are related but not identical concerns. A calculation may estimate tissue gas tensions, while bubble formation and the body’s response involve additional biological processes. This distinction helps explain why decompression remains a field of research rather than a simple pressure-and-time calculation.

Inert-gas uptake: gas enters tissues as exposure pressure rises.
Inert-gas elimination: gas returns to the circulation and is removed through the lungs.
Supersaturation: tissue gas pressure exceeds the surrounding pressure, creating conditions in which bubbles may form or grow.
Decompression schedule: a planned ascent, including any required pauses, intended to manage changing pressure and gas loading.

How does this theory connect to diving practice?

Divers use decompression procedures to manage the pressure change from depth to the surface. The relevant exposure includes the depth profile, time, breathing gas and ascent; a schedule cannot be separated from the dive it is meant to control. Repetitive dives add another layer because residual inert gas from an earlier exposure affects the next one.

For diving physicians, decompression theory provides a framework for understanding decompression illness, but it does not replace clinical assessment. Symptoms after a dive need timely evaluation by a diving-medicine physician, since presentation and severity vary and other conditions can resemble decompression illness.

Scientific divers face the same physiological constraints while also working around task requirements, equipment and environmental conditions. Planning must account for the actual exposure and the consequences of an ascent interruption, not just the nominal profile.

Where does Hills fit in the history of the field?

Hills belongs to a longer effort to make decompression more physiologically grounded. Early practical approaches relied heavily on observed dive exposures and empirical rules. Later modelling brought gas kinetics and compartment concepts into a more explicit account of how pressure histories affect the body.

The wider field continues to examine where models agree, where they diverge and what biological processes they leave out. Decompression tables and dive-computer algorithms are practical applications of models; their outputs are not interchangeable simply because they share the language of compartments or tissue loading.

Reading Hills in this context means treating decompression as both a physiological problem and a modelling problem. The useful question is how an assumption about gas behaviour shapes a real ascent plan—and what that plan can and cannot represent.

What should divers and clinicians keep in mind?

Decompression procedures are designed for defined exposure conditions. Changing the breathing gas, extending the dive, making an unplanned ascent or repeating dives alters the problem. A computer or table should be used within its stated operating assumptions and alongside established training and procedures.

No model guarantees that decompression illness will not occur. If symptoms develop after diving, seek urgent assessment from a diving-medicine physician rather than relying on a decompression calculation to judge their significance.

Frequently asked questions

Who was Brian Andrew Hills in diving science?

Brian Andrew Hills is associated with decompression theory, the study of how pressure changes and inert-gas movement affect divers during ascent.

What does a decompression model try to represent?

It estimates inert-gas uptake and elimination across a dive and uses those estimates to inform an ascent schedule. The model simplifies biological processes that cannot be represented by one calculation alone.

Does following a decompression schedule rule out decompression illness?

No. A schedule manages an exposure according to its assumptions, but it cannot guarantee an individual outcome. Symptoms after diving need assessment by a diving-medicine physician.

An original research-library explainer written by the Rubicon editors. It is not a summary of a specific publication.