Is That Welding Oxygen in Your Nitrox Tank?

In most countries there are no universal standards for handling Nitrox, so regulations and practices vary from location to location. In fact, operations in countries such as St. Eustatius, Belize, Fiji, Papua New Guinea and nearly all distant dive venues use industrial grade (i.e., welding) oxygen in their mixes. Medical grade oxygen is either unavailable or prohibitively expensive, they say.

While ANDI recommends that only gas rated for human consumption be used for diving, apparently the risk of contaminants in industrial grade oxygen is generally low. As PSI's Bill High told Undercurrent, both medical grade and industrial grade oxygen "come out of the same faucet." The difference is in how storage cylinders are handled. Industrial grade oxygen cylinders are returned for filling while still slightly pressurized. New oxygen is added on top of the old gas. Medical grade cylinders are vacuum cleaned to clear out any cross contaminants that may have slipped through the manifold when the cylinder was in use.

If you're nervous about getting a Nitrox fill from a foreign dive operator, ANDI's Charlie Johnson suggests you ask to see their most recent air analysis certificates. Standards vary widely, so you'll probably need to have the operator interpret the results for you. But if there's a history of the air being tested frequently and recently (every three months), that's a good indicator that the operator is being careful.

Dedicated Nitrox divers often carry their own oxygen analyzers to measure the oxygen content in their mixes. Charlie Johnson says that other kits are available that can detect gross amounts of carbon monoxide.