Not if you use it in the manner I described. The potential danger with helium is that it is a very light substance which ongasses and offgasses very quickly. If you're using it for your dive, you should take that into account for your ascent rate ... it's much easier to bend yourself on helium than on air or nitrox. But for a minute worth of breathing at depth, it won't really change anything except your sensory perception ... in effect, you'll suddenly realize how narc'ed you were before switching to it. Switching back to your own gas, you will also be more aware of how narc'ed you become. Now you will have a better comprehension of how insidious narcosis is, and how narc'ed you've been at those depths without even realizing it.
... Bob (Grateful Diver)
Agreed. It was not uncommon at one point in a trimix class to breathe off a stage with air at depth to feel the sudden onset of the narcosis that you other wise fail to notice with a gradual descent. And similarly, in a extended range class, briefly breathing off a stage of trimix would lift the fog so to speak and make the point that trimix is a pretty good idea.
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Trimix fills, starting from zero psi can be a little spendy and I have spent $125 for a fill in 130 cu ft doubles in the past when getting trimix at a shop in Alexandria VA that did not sell a lot of it.
However, my experience in south Florida is that a 30-40 minute bottom time dive in the 170-210 ft range with gasses in the 21/35 and 18/45 ranges will cost about $20-$30 for the trimix and deco gas actually used. Given the cost of the boat ride, motel, meals, gas to get there, etc, the cost of the gas is minimal, and almost insignificant when you subtract the cost of the air fill and deco gasses you'd have needed anyway to do the same dive on air.
For that additional $10-$15 cost of trimix you get a much lower END creating a much greater level of safety on the dive and allowing you to observe more on the dive and remember much more of the dive.
When doing N FL cave dives in the same depth range, the additional cost is probably also in the $10-$15 dollar per dive range (it's harder for me to calculate as we run a tab for the week and make one large payment at the end of the week for O2 nitrox and trimix), but the SA and safety benefits make that extra cost a bargain. In addition, being slighty cheap, I'll plan deeper cave dives early in the week and then top off one pair of tanks with the ever present 32% nitrox for subsequent 100-110 ft range dives. The He percentage declines while the O2 percent increases with each top, and while it's not what you'd call a standard gas, you do gain some END benefit over the course of a few more dives for basically no added cost on that trip.