The EAC is a long sheet of a matrix of plastic embedded with absorbent (the exact same chemistry as granular). It's rolled up into a cylinder which can be unrolled (like you would unroll paper towels). The unused material is very flexible and white... when used the portion that is consumed becomes noticably harder and discolors (a slight yellowing)... by unrolling its very easy to determine rather precisely how much has been consumed just by feel. Done repetitively, the user of the EAC can determine how much of the EAC is being consumed by their specific metabolism and specific dive conditions. This works because the EAC is extremely consistent from cartridge to cartridge (mfg says within 5%, in my experience much better than that).

Note, Dive Rite is now rating the EAC when used in the O2ptima for 240 liters of CO2. If you track your oxygen consumption, this means you can more reliably determine the life of the EAC... for many divers this means substantially more life than 3 hours (usually somewhere between 4 to 5 hours, some individuals much more or less) and still remain within mfg specifications. Again, this works because the EAC is very consistent without concern for packing varation or channelling issues.

For example: Assume the user is using al-13's (13 cu ft of o2 at 3000 psi). If you assume that the diver produces .9 liters of CO2 for every 1 liter of O2, then when 266 liters of O2 have been consumed 240 liters of CO2 have been produced. At 28.3 liters per cubic foot, 266 liters would be about 9.4 cubic feet of O2, or 9.4 / 13 * 3000 = 2170 psi of O2. So, when the diver has used about 2200 psi of O2 from their cylinder (i.e. 800 psi remaining from a full fill) they need a cartridge change. For myself, this equates to about 6 hours of non-deco diving (where I'm not doing a lot of O2 flushing on deco stops), including the O2 I used to do one calibration. [Numerous varations and refinements are possible if you like: use 1 liter of O2 consumed equals 1 liter of CO2 produced, make adjustments for calibrations, waste on ascents, O2 that came from Dil, yada... yada...]

If the EAC user does not wish to track O2 consumption (and therefore CO2 production) then they can choose to fall back on the 3 hour time duration previously recommended if they wish to remain within mfg specifications for duration.

Note this discussion applies only to the EAC EP cartridge as used in the O2ptima.


-- Mark