RATIO DECO –
The science
By Andrew Georgitsis
About 5 years ago two diving physicians in Italy become very interested in scientifically testing UTD’s
Ratio Deco ascent strategy. Their idea was to test the effectiveness and efficacy of some of the concepts
in Ratio Deco such as S-Curves. They would test it against a modified Bulhmann model to keep many
of the Ratio Deco components consistent – protocols such as the choice of gasses and deep stops. This
would objectively test UTD Ratio Deco S-Curves and thenemphasis on O2 windows to dramatically
improve decompression. The doctors were testing several parameters including: 1. A reduction in the
blood cell dust. 2. No activation of the body’s immune system. 3. Bubble formation and elimination.
UTD Ratio Deco rules are simple and well defined, however to truly better understand the core of Ratio
Deco as a strategy, let’s look at some of the history. I first used Ratio Deco in 1996 as a memorization
technique and then later, in 1997, added a set of “rules of thumb” for deep stops. These deep stop ideas
were emerging from the WKKP. We wanted an easy way to add WKPP “Deep Stops” to our Bulhmann
Profiles. The rules I developed were to keep the system simple and easy. At that time the director of
WKPP, George Irvine, had proposed that the first deep stops were to be at 80% of the ATA’s (Atmospheres Absolute). This was difficult for teaching and diving – new technical divers would need to do
their calculations “on the fly,” and in the imperial system they first would need to convert their depth
(feet) into ATA’s, then calculate the 80% of the ATA’s, and then convert the resulting ATA’s back to feet,
a difficult task without a calculator, let alone at depth. So, it was much easier for me to teach a “rule of
thumb” that divers could do simply and easily – we called it “scuba math.” Simply we did 75% of the
depth for deco dives and 50% of depth for non-deco dives. The math was easier and the results were so
close to the 80% rule that it did not really matter – we were rounding shallower to the nearest 10’/3m
mark anyway.
Then in the late 90’s Erik Baker released his Deco Software which allowed us to implement the “Workman” adjustments (gradient factor HI and gradient factor LO) to a Bulhmann profile. Thi ́