I achieve a "stressed SAC" by calculating the weighted average rate for a given gas, usually in two runs. (It's rare the timing lines up with the switch schedule, so one of the gases will be split across 2 rates.)
For instance, for a 10 minute stressed SAC of 1.8 cuft/min. Say from initial BO to the first switch is under 10 mins, so it's obviously at the 1.8 cuft/min rate. If the first deco gas lasts longer than the remaining stressed time, use the average. Say there's 9 minutes on the first deco gas, but the switch to that gas is 6 mins after the initial BO. That means 4 mins of stressed SAC (to reach the end of the 10 min period), which is 44% (=4/9) of the total time for that gas. The other 56% is at the reduced SAC of 0.9 cuft/min. The average rate is therefore 0.44*1.8 + 0.56*0.9 = 1.3 cuft/min. Use that effective rate in the planner for the deco SAC and get that first deco volume. Then re-run at the 0.9 rate to get the volumes for the remaining deco gases.
It would be great if this were built-in, but it should only take you 2 runs to get your volumes.
For instance, for a 10 minute stressed SAC of 1.8 cuft/min. Say from initial BO to the first switch is under 10 mins, so it's obviously at the 1.8 cuft/min rate. If the first deco gas lasts longer than the remaining stressed time, use the average. Say there's 9 minutes on the first deco gas, but the switch to that gas is 6 mins after the initial BO. That means 4 mins of stressed SAC (to reach the end of the 10 min period), which is 44% (=4/9) of the total time for that gas. The other 56% is at the reduced SAC of 0.9 cuft/min. The average rate is therefore 0.44*1.8 + 0.56*0.9 = 1.3 cuft/min. Use that effective rate in the planner for the deco SAC and get that first deco volume. Then re-run at the 0.9 rate to get the volumes for the remaining deco gases.
It would be great if this were built-in, but it should only take you 2 runs to get your volumes.
