In Section Four you learned the basics for diving with dive tables and dive computers, but there are some additional procedures that you need to know about. These involve procedures for enhanced safety, for accidentally exceeding your no-stop limit, and for diving at altitude or ascending to altitude after diving.

Safety Stop 
Although as a recreational diver you plan only no decompression dives that allow you to ascend directly and continuously to the surface, most of the time you'll want to make a safety stop for added conservatism. A safety up provides extra time for your body to eliminate nitrogen, and it gives you a moment to stabilize and control your ascent tie before continuing to the surface.
 


To make a safety stop, you stop your ascent the 3 to 6 metre/10 to 20 foot range usually at 5 metres/15 feet for three minutes or longer. It's easiest to do this holding into or on an ascending slope, but you can also hover in midwater where appropriate.

You plan your dive so you can make a safety stop and still reach the surface with 20-40 bar/300-500 psi or more air remaining in your cylinder.

You may make a safety stop at the end of any dive, and in fact, you should consider it a standard practice on virtually all your dives. However, consider a safety stop required if:

  • Your dive has been to 30 metres/100 feet or deeper.
  • Your pressure group at the end of the dive is within three pressure groups of the no decompression limit on the RDP.
  • You reach any limit on the Recreational Dive planner or your dive computer. With a dive computer, this would be if your computer shows zero NDL time remaining at any point in the dive.

When using the RDP, in these circumstances the safety stop is considered required.
You may wonder whether you need to account I for safety stop time when using the RDP. You don't need to add safety stop to your bottom time when using the Recreational Dive Planner. A computer will process safety stop time automatically.

Keep in mind that, although you should make safety stops a regular procedure for all your dives, it's optional under circumstances such as very low air (due to unforeseen circumstances during the dive), assisting another diver, or rising bad weather make it more important to get to the surface immediately.

Emergency Decompression
You plan your dive as a no decompression dive but emergency decompression stop to allow your body to eliminate nitrogen; without this stop, you face an unacceptable of DCS when you surface.

You exceed a no decompression limit or an adjusted no decompression limit by more than five minutes, 5 metre/15 foot stop for no less than 15 minutes is strongly urged, air supply permitting, you must remain out of the water at least 24 hours before diving again, due to the excess nitrogen in your body.

When making a emergency as close to 5 metres/15 feet as possible. If you don't have enough air for the emergency decompression stop, stay as long as you can, saving enough air to surface and exit safely. Discontinue diving for no less than 24 hours. Breathe pure oxygen if available and monitor yourself for decompression sickness symptoms.

Using a dive computer: If you exceed your computer's no decompression limits, it will go into decompression mode, which guides you through the emergency decompression top. Computers differ in how they function in decompression mode. So consult the manufacturer's literature for the specifics for your computer. Many will show emergency decompression stops at 3 metres/10 feet instead of 5 metres/15 feet: stopping at 5 metres/15 feet until the computer says you can surface will still work, though, because the computer calculates the stop based on your actual depth. It may take a bit 1 on; than the time indicated for a stop at 3 metres/10 feet.

It's not recommended that you make a repetitive after a dive requiring emergency decompression. Emergency decompression stops differ from safety stops in that an emergency decompression stop must be made or there is an excessive risk of decompression sickness, and that is an emergency procedure.

Altitude Diving. Thinking back to Section One, you recall that as you ascend in air, pressure decreases. Dive tables and most computers give you their no decompression limits based on a dive ending at sea level: if you're under less pressure at altitude, nitrogen comes out of solution more following a given dive, making decompression sickness more likely.

You can use the Recreational Dive Planner for diving to altitudes as high as 300 metres/1000 feet. Above 300 metres/1000 feet, you need special conversion tables and procedures to account for the decreased atmospheric pressure or you can run an unacceptable risk of DCI.
 


The procedures for diving at altitude with a dive computer vary with the computer. Some automatically compensate for altitude, where as with others You'll need to tell the computer your altitude. There are a few older models that you can't use at altitude.

You also need to think about lowered atmospheric pressure if you plan to fly after diving. While this concern is similar to altitude diving, it's not identical. When you dive at altitude, you dive and return to reduced atmospheric pressure. When you fly after diving, you dive and return to normal atmospheric pressure, then expose yourself to further pressure reduction.

The dive medical community offers the following general recommendations for flying after diving. whether you're using the RDP. another table or a dive computer:

For Dives within the No-Decompression Limits. 

  • Single Dives - A minimum pre interval of' 12 hours is suggested.
  • Repetitive Dives and/or Multiday Dives A minimum preflight surface interval of 18 hours in suggested For Dives Requiring Decompression Stop.
  • A minimum preflight surface interval of 18 hours in suggested.

Flying after diving recommendations change over time. These are current at the time of printing. Always check with your instructor to stay apprised of the most current ones.

For Dives Requiring Decompression Stops
As with dive tables and computers, no flaying diving after diving recommendation can guarantee that decompression sickness will never occur. These guidelines represent the best estimate presently known for a conservative. safe surface interval for the vast majority of divers. There always may be an occasional diver whose physiological makeup or special dive circum tances result in decompression sickness despite following the recommendations.

You're responsible for your own dive safety and behavior. Flying after diving recommendations change as we learn more about how pressure changes affect the body: stay current and follow the most current recommendations.

There are currently no recommendations for driving to altitude after diving, so the most prudent practice is to be conservative. The longer you wait before you go, the lower your risk. You may check with a local dive center, resort or instructor to see if divers in the area follow a particular recommended or protocol.

If you get cold or exercise a lot during a dive, you may end your dive with more excess nitrogen in your body than calculated by your dive table or computer. When using the RDP for planning a dive in cold water or under conditions that may be more strenuous than usualy, plan our dive as though the depth were 4 metres/10 feet deeper than it actually is.

How you handle this with a dive computer depends on the computer. A few sophisticated models track the water temperature and your breathing rate and automatically readjust to more conservative no stop times when necessary. For others, you can set the computer to be more conservative by using the altitude setting and setting it to an altitude higher than, you actually are, or by connecting the dive computer to a personal computer (requires special hardware and software). However. you have to make these setting before the dive. If you can t set your computer to be more conservative

1.When using the RDP. you need to use special dive procedures above what altitude?
2 The minimum recommended surface interval for flying after diving is
3.Using the RDP. under cold and strenuous conditions you plan your dive as though:

a. It were at altitude.
b. It were 4 m/10 ft deeper than actual.
c. It were 4 m/10 ft shallower than actual.
d. None of the above.