DA Aquamaster once bubbled...
The "new" PADI table uses a 6 hour out and the underlying assumption that you completly off gas in 6 hours - a very dubious assumption. The Navy/old PADI table assumed a 12 hour out, so in effect you have more "fineness" in the new PADI tables and groups but only because the table is operating in a much more restricted range in terms of offgassing. The last thing I would call it is safer particlarly on multiple dives over multiple days. The "new" RDP is also one of the most liberal of the current crop of dive tables around.
The apparent "liberalness" of the PADI RDP is because it recognizes that the 60 minute halftime compartment is the slowest controlling compartment in normal recreational diving.
The PADI RDP tracks only the 60 minute compartment. 6 hour SI will reduce that compartment to only 1.6% loading above normal sea level loading. For all reasonable people, that is fully offgassed. This is particularly true since you will only reach Y or Z pressure groups (92% or 95% of DSAT 60 minute M value I believe, where 24.8fsw absolute is 0%) by shallow dives that exceed 120 minutes in length.
All dives deeper than 40' hit NDL based on faster compartments, but then the N2 decay during SI is calculated using a 60 minute HT, resulting in extra conservatism.
I have not reverse engineered the Navy tables since they don't seem to be consistent. They do however seem to be primarily based on the 120 minute compartment, which is not the limiting compartment for normal rec diving.
Slower compartments only become the limiting compartments for very, very long shallow dives. Those dives are controlled on the PADI RDP by the fine print on the back, with restrictions on repetitive dives if you enter W, X, Y, or Z pressure groups. Those restrictions keep your average depth (including SI) no more than 23' and thereby keep from loading up the slowest compartments beyond limits.
The M values upon what the DSAT/PADI table are based are more conservative than the Navy (Workman 1965) in each and every compartment. The DSAT values are similar to the ZHL16 values -- a little more liberal for 5 or 10 minutes (5, 8, 12.5 for ZHL16) compartments; more conservative for most.