Maximum tissue pressure allowed in the compartment when the diver surfaces.

The faster the compartment (shorter halftime), the higher the M-value (the more nitrogen it is allowed to have when surfacing); the slower the compartment, the lower the M-value.

You need to know the altitude when diving because most decompression models are based on surfacing sea level.

CONTROLLING COMPARTMENT = the compartment that reaches the M-value first

The faster the compartment, the shorter halftime.
The slower the compartment, the lower the M-value
The higher the M-value, the more nitrogen it is allowed to have upon surfacing.
M-values are from A to Z in the RDP

The US Navy tables were developed primarily for military decompression diving. They were used for recreational diving because:

• They were widely available.
• Many early recreational divers were former military divers.
• Before the rise of dive computers.

US NAVY	HALDANE MODEL
6 compartment model	5 compartment model
120 minute halftime	75 minute halftime the longest compartment
surface interval credit for the next dive	no provisions for repetitive dive

In 1987 PADI Divemaster Dr. Raymond E. Rogers designed a table adequate for recreational diving.

You can’t interchange Pressure Groups between the RDP and the US Navy tables because they’re based on two different models.

The RDP was originally introduced in two forms (table & wheel). The eRDP (electronic RDP) is the newest and third format available.

RDP	US NAVY
No decompression (recreative) dives	Stage of decompression use
14 compartment model	6 compartment model
60 minutes surface credit	120 minutes surface credit
Halftimes with faster gas washout (6 hours)	Halftimes slower gas washout (12 hours)
Designed for multiple dives a day with shorter surface interval	Designed for military use (limited dives a day with a longer surface interval)
Represent a wide part of the population	Taste only in military young male subjects.
More appropriate M-values (Doopler detected bubbles)	M-values based on DCS / no DCS

Computers essentially write custom dive tables for exact dives

• Eliminates unnecessary rounding
• Longer dive times

SPENCER LIMITS 60 MINUTES WASHOUT
RDP-like No Deco limits, 60 minutes surface interval credit

SPENCER LIMITS EE WASHOUT
EE (= Experimental Exponential)
RDP-like No Deco limits, compartments washout are underwater rate.

BUHLMAN LIMITS EE WASHOUT
Shorter than RDP limits, compartments washout are underwater rate

Cold/strenuous dives – plan as if 4m deeper than actual

Each successive dive is to the same or shallower depth

Limit the depth according to your training and experience

With multiple repetitive dives:

• W or X – 1 hour surface interval on all subsequent dives
• Y or Z – 3 hour surface interval on all subsequent dives

Repetitive Dive limit – 30 m

Maximum Recreational Depth limit – 40 m
If you accidentally go deeper?

• Emergency decompression stop for 8 minutes at 5m
• Do not dive again for at least 6 hours

Safety Stops

• Recommended: after every dive
• Required after:
  • Any dive to or deeper than 30m;
  • Any dive made within 3 pressure groups of NDL;
  • Any dive reaches any limit on the RDP

Emergency Decompressions

• 8 min at 5m when limit is exceeded by 5 min or less
• 15 min at 5m (or as long as air supply permits) when limit is exceeded by more than 5 min

Omitted Decompression

• Do not reenter the water
• Do not dive for at least 24 hours
• Monitor for signs or symptoms of DCS
• Breathe oxygen and seek medical assistance if signs/symptoms occur

Altitude Considerations – Special procedure must be implemented when using the RDP at altitudes greater than 300m

Flying After Diving

• Minimum surface interval of 12 hours
• Divers who plan to make daily, multiple dives for several days or make dives that require decompression stops should take a special precaution — 18 hours before flight.

Procedure if your computer fails

• Slowly ascend to 5m and make a safety stop — extended if necessary
• If your dive profile is within no stop limits, you may be able to resume diving using the RDP
• If not, stay out of the water according to manufacturer recommendation