![]() In extreme conditions, decompression risk can be traded for operational risk by using the GF99 display. Above 100% it is displayed in flashing red. It switches to yellow when the GF99 exceeds the value defined by the GF conservatism settings. Once a super-saturation exists, the GF99 is displayed in green. If no super-saturation exists, then the GF99 displays “On Gas”. The GF99 value shows the current super-saturation as a percentage of Bühlmann’s original limits. Between the deepest stop and the surface the GF limit is linearly interpolated. The default GF high value of 80% sets the surfacing limit. The default GF low value of 30% limits the super-saturation gradient at the deepest stop. The GF low and high conservatism settings are used to scale Bühlmann’s original limits to reduce risk of decompression sickness. A value of 100% (Bühlmann’s originally allowed super-saturation limit) is now generally accepted to be too risky. This value can be used as a rough measure of the current decompression risk. If that sounds confusing, then recommended reading is Erik Baker’s paper, “Clearing Up Confusing About Deep Stops”. The GF99 value shows the current leading tissue inert gas super-saturation percent gradient as defined by the Bühlmann ZHL-16C decompression model.
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