If it’s maximum bottom time you are wanting to achieve, trimix could be exactly what you’re looking for. When I started diving and looked at the standard dive tables I could not imagine why anyone would want to go all the way to 100ft just to have to stay down for 5 minutes and make their way back up to the surface (after the mandatory safety stop, of course). If I was going to spend all that time descending, equalizing and making sure my buddy and I made it to the bottom with me you can be sure I was going to hang around the bottom long enough to explore. Enter, trimix.
This little wonder of a breathable gas cocktail has been maximizing bottom time for much of the 20th century and, if used properly, can mean the difference between 5 minutes and 25 minutes exploring that shipwreck in 100 feet or more of water. While additional bottom time can be achieved by getting a Nitrox (enriched air) certification, trimix is more advantageous at depth because it adds helium in to the mix which does a few positive things for the aspiring Underwater Ninja.
First, and most importantly, the addition of helium lowers the proportion of oxygen being introduced in to the body which greatly lowers the risk of oxygen toxicity (oxygen poisoning). For those of you new to diving, oxygen toxicity means lights out for any diver. Switching to a lower oxygen mix at this depth greatly reduces your risk of oxygen poisoning. Secondly, helium is lighter than nitrogen which means that it leaves the body more easily which will help aid in off-gassing as you come to the surface and throughout your surface interval.
One thing to watch out for is the effect of trimix on the algorithms in your dive computer. Helium has differing effects on the body and should be accounted for when preparing your dive computer for the dive. I would consult your owners manual to insure you have your dive computer properly configured. That said, there are several standard mixes of trimix that are used which means finding appropriate dive tables or dive computer algorithms is relatively straightforward. Trimix air proportions are measured as percentage of oxygen percentage then helium then (sometimes) nitrogen. If the third number is not given it is assumed the balance is nitrogen. Simply, the lower the oxygen the deeper the air is meant to be used. A popular ‘bottom gas’ is hypoxic trimix or 10/50 and this is not suitable to be breathed on the surface. A separate air source is meant to be used to reach the bottom and hypoxic trimix is to be used once depth has been achieved.
The information around trimix can be a bit intimidating at first, especially because your life is at risk, but if used properly it can mean much more bottom time and much more overall enjoyment for the aspiring Underwater Ninja.