scuba

Question
What is the minimum surface interval required between a dive to 60 feet for 40 minutes followed by a dive to 50 feet for 60 minutes?  

Answer
The answer depends a lot on what dive table you are using.  The PADI and SSI and Navy tables are all slightly different.

So I will give you a generic method to figure it out.

Using Table 1, determine the pressure group of your dive to 60 feet for 40 minutes first.  Let's say you get a group 'G'.

Using Table 3, look across the row for 50 feet.  You need to find the entry for an Adjusted No-Decompression Limit that is closest to 60 minutes (but not less than 60).  For the table I looked at, it was 64 minutes.  Look upwards in that column to see what pressure group that is.  In my case it was 'A'.

Go to Table 2 and determine what minimum surface interval would be required to go from the 1st dive pressure group (in this example 'G'), to the desired pressure group you just determined (in this example, 'A').  For the tables I used, that would have been 7 hours 36 minutes.  

Tht would be a long time indeed.  Note that it is also unlikely you would actually have enough air to do a 60 minute dive at 50 feet.  If you shortened the 2nd dive to 41 minutes, you would only have to be a 'D' diver before starting the second dive.  The SI to go from G to D would only be 2 hours.

Hope this helps...JS