Open-circuit technical divers often switch to breathing pure oxygen or a very rich advanced Nitrox mix such as 50%, to substantially reduce their required-stop times as compared to decompressing using just their bottom mix, called accelerated decompression. The depth where the gas switch occurs is relatively shallow, typically {20 fsw | 6 msw} for 100% oxygen or { 70 fsw | 21 msw} for 50% Nitrox. For profiles with very deep and/or very long bottom times, the diver can further reduce their required-stop times with multiple gas switches during the ascent, sometimes called multi-staged accelerated decompression (not to be confused with regulator stages). The depths where the first gas switch occurs in multi-staged deco is relatively deep, typically {100 fsw | 30 msw} using a sport Nitrox mixture and for extreme exposures often the first switch is around {190 fsw | 57 msw} using normoxic Trimix.
Divers on decompression stops are normally at rest and decompression gas regulators are typically configured with only one second stage regulator. Required-stop decompression in general is not an activity that demands high-performance regulators, although it can be in physical overhead environments where the diver must also continue swimming towards an exit. The shallower accelerated decompression depths when using very oxygen rich breathing gases are not at all demanding of regulator performance, almost any regulator would do in theory, but the very rich decompression gas requires the regulator be specifically designated as suitable for use with pure oxygen. Unfortunately, most manufacturers only describe their regulators as suitable for Nitrox mixtures to 40% maximum.
Dive Gear Express offers several specialty decompression regulators all designed and qualified for use with breathing gas mixtures containing up to 100% oxygen, but each suitable for use in differing maximum depth ranges based on their performance. The Dive Rite O2 Regulator is suitable to a maximum depth of { 50 fsw | 15 msw}. The DGX Gears O2 Regulator is suitable to a depth of {130 fsw | 40 msw}. The Mares O2/Stage Regulators are suitable for use to a depth of {160 fsw | 50 msw}. The Dive Rite O2/Stage Regulator and the Apeks O2/Stage Regulator depth limits exceed {330 fsw | 100 msw}. For reasons of familiarity and ease of maintenance irrespective of cost, divers will sometimes choose to use deco regulator versions similar their primary even though their performance exceeds the demands of required-stop accelerated decompression.
Regardless of the capabilities of your regulator, the maximum depth of your dive is also limited by the amount of oxygen in the breathing gas and the partial pressure of oxygen at that depth.
