Analysis of the mixtures & Cylinders and Cylinder Markings

Analysis of the mixtures

As in EANx, you will also be responsible for the analysis of mixtures thereof. The difference is that now we have the presence of helium. There are few places that have Helium analyzers. Therefore, generally only analyzed the oxygen which is the most critical factor of the mixture due to intoxication involved. A variation on the Helium percentage more or less will make a difference only in your END. Already a variation in oxygen may expose the diver to the risk of decompression sickness and toxicity. During the analysis process remember:

  • Calibrate the analyzer
  • Use flowmeter whenever possible
  • A +/- 1% variation is acceptable
  • Wait for the reading to stabilize

Cylinders and Cylinder Markings

Cylinders should be oxygen clean. As the dives are made deeper and for longer times, it is recommended to use cylinders with larger capacities. In this way, we can better enjoy the dive. The nomenclature used for any mixture of Trimix (Recreational or not) is the same. While the mixture is composed of three gases, only the oxygen and helium percentages will be represented in the label. Nitrogen will be assumptive as shown in the following example:

Example 1: a mixture of Recreational Trimix containing 32% oxygen, 15% helium and 55% of nitrogen is represented by 32 / 15.

Example 2: A mixture of Recreational Trimix containing 28% oxygen, 25% helium and 47% of nitrogen is represented by 28 / 25.

The oxygen percentage is to the left and right is the Helium percentage in the mix, always separated by a single slash. For IANTD Recreational Trimix courses, three common gases that may be used are 21/35, 28/25, and 32/15. You and your instructor will use the recreational trimix mix based upon your dive plan.

The cylinder identification process is very important to prevent errors during handling and use of mixtures. Both the bottom gas cylinders as the decompression must be properly identified. The information to be displayed are:

  • Mixture; on the neck and bottom of the cylinder
  • Diver’s name
  • Date mixture

The several types of marking a tank include the following:

  • Permanent Marking: the diver prints the MOD permanently on the cylinder. The downside is that you need to own the cylinder, which is dedicated to a unique blend. Retouching of the markings has to be done periodically. In this case, although the cylinder is dedicated to a single mix and labeled, the analysis of the content should always be performed so that no accidents occur.
  • IANTD Marking Stickers: the IANTD has two types of content labeling stickers. The diver can buy the stickers with the desired MODs and affix them to the bottom of the cylinder, or purchase a sticker on which there is a blank space where the MOD can be written with marker. This sticker can be reused for different mixtures as the diver may be able to erase the MOD mark. In this manner, it is not necessary to dedicate or have your own cylinder. This sticker will have a useful life far less than the permanent markings.
  • Marking “Duct Tape”: this is the marking most used by divers as it has a low cost compared to the others. In this type of marking, it is not necessary to dedicate or have your own cylinder. Again, using DUCT TAPE will not last as long as the permanent marking but the temporary nature of the marking my provide a benefit to a diver with limited equipment to dedicate to a single gas.

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