Cavern/Intro Cave

At the cavern and intro to cave level we dive to a maximum penetration of ⅙ of our gas. We use ⅙ on the exit and the remaining 4/6 (⅔) is reserve gas for emergencies. It is common to do 2 dives on 1 set of tanks at the Intro level, but adequate gas to complete the dive, and a safety stop is always required. This level is restricted to ⅙ to prevent divers from progressing far into the cave environment. By limiting penetration it reduces distance stress while still allowing divers to build their skillsets in the overhead environment.

LP85s or LP108s are appropriate for cavern/intro. Aluminum 80s could be used but they don’t have adequate volume for many of the deeper Florida caves.

Full Cave

At the full cave level we can use up to ⅓ of our cylinders entering the cave. That leaves ⅓ for the exit and the last ⅓ is reserve gas for emergencies.

This is a maximum amount of gas ideal for teams of 3 in high flow caves. There are plenty of reasons to be more conservative than diving thirds. To be more conservative we use the “thirds plus” methodology. If we have 3,000psi we will use 1,000psi and turn at 2,000psi. If we wanted a buffer we could say that our turn is 2,000psi+200psi so we turn the dive at 2200psi instead of 2,000psi. Adding the buffer gives us more reserve gas because our exit gas usage will likely match our entrance gas usage. We used 800psi on the entrance, 800psi on the exit and we will have 400psi extra in reserve over standard thirds diving. The appropriate amount of buffer depends on the dive.

Examples of when to use the thirds plus methodology:

• Diving in a team of 2.
• Siphon or no flow cave.
• Small cave where you may be exiting in zero viz (takes longer to exit).

LP108s are the most appropriate cylinder for a full cave course in Florida. LP85s work but you get to see more cave with 108s. An aluminum 40 for oxygen is required for decompression at the full cave level.

Dissimilar Gas Volumes

Stage Cave

Aluminum 80s can be used to extend our dive time in the cave environment. We breathe them on the way in, clip them to the line, and pick them up on the way out. There are many ways to manage gas in a stage. You can use standard thirds, methodology but that’s not ideal. Instead of treating them like our mains and breathing ⅓ in we use more out of the 80 than ⅓ and keep the contingency gas in our mains. By “moving” gas to your mains you reduce time you’ll have greater flexibility in the exit if there’s an emergency. Half plus 200 isn’t appropriate for all dives, but the basic math is listed below.

• Breathe half plus 200psi from the stage. That means it gets dropped at 1700psi.
• Add the remaining gas from the 80’s third to your mains. In LP108s, you add 100psi to your thirds. That is equal to 300psi from the 80.

Aluminum 80cuft with 3,000psi

• 1,000psi = 27cuft
• 100psi – 2.7cuft
• Normal thirds – Turn is 2,000psi = 27cuft used
• Half plus 200psi – Turn is 1700psi = 34cuft used
• 34cuft-27cuft=7cuft

LP 108 doubles with 3800psi

• 100psi = 8.2cuft
• By adding 100psi to our mains we’ve “moved” 300psi from the 80 to our mains.