What depth needs trimix?

Most agencies set the air and nitrox limit around 130 to 150 feet. Past that, helium keeps your equivalent narcotic depth and oxygen partial pressure within safe limits. Trips are planned to 200, 250, or 300 feet depending on your cert.

How much does helium cost?

Enough that it is priced per fill and listed separately. A single deep dive can use $100 to $300 in helium depending on the mix and destination. Ask for the fill price list before you book.

Can I do this on open circuit?

Yes, most trimix trips support both open circuit and CCR. Open circuit needs more cylinders and more helium; CCR needs bailout planned for the whole dive. Teams usually mix both.

Trimix Dive Expeditions: Deep, Planned, Supported

Below 150 feet, air is narcosis and oxygen toxicity waiting to happen. Trimix swaps part of it for helium and gives you a clear head at 200 feet. That comes with gas planning, deco obligations, and a dependence on the operator's support boat that you need to trust.