Dive Physics 2 Flashcards
Descent Time
-Total elapsed time from when the divers LEAVE the SURFACE to the time when they REACH the BOTTOM
Max rate of Descent
- 75 feet per minute max
- Round to next nearest whole minute (ex. 53 fsw = 43 seconds = 1 minute)
Bottom Time
(BT)
- Total elapsed time from when the divers LEAVE the SURFACE to the time they LEAVE the BOTTOM
- Round to the nearest whole minute
Total Decompression Time
(TDT)
-Total elapsed time from the time the diver LEAVES the BOTTOM to the time they ARRIVE on SURFACE
Max Ascent Rate
- 30 fpm
- 1 ft / 2 seconds
- Time needed to “off-gas”
Decompression Table
- Structured set of decompression schedules or limits
- Organized in order of increasing bottom times and depths
Decompression Schedules
- Specific decompression procedure for a combination of DEPTH and BOTTOM TIME
- Indicated as feet/minutes
Decompression Stop
- Specified depth a diver must remain at for a specified time
- Eliminates inert gasses from the body
- “Lets the fizz out”
Deepest Depth
-Deepest reading on depth gauge during a dive
Max Depth
- Deepest depth attained after correcting depth gauge for error
- Max depth is used on decompression table
Scuba Max Depth
- Max depth and deepest depth are the same
- Gauges in scuba are considered error free
Surface-Supplied Max Depth
- Surface Supplied uses “pnneumofathometer” not dive gauge
- max depth is = deepest reading on pneumo gauge + pneumo correction factor
- Gauges on surface supplied not considered error free
Unlimited / No decompression Limits
(No D)
-Max amount of time that can be spent at a given depth such that safe ascent can be made directly to surface with no stops
Types of Decompression Tables
1) Unlimited / No D Limits
- All scuba dives should be here
2) Residual Nitrogen Timetables
- Used for “repet” dives
- RNT
3) Air Decompression Table
Unlimited / No D Table
-Identifies that on dives in 20 fsw and shallower, unlimited bottom time can be achieved
Selection of Decompression Schedule
- Select schedule at the EXACT or NEXT LONGER bottom time of the dive
- Deviations from established decompression procedures are not permitted except in an emergency and with the guidance and recommendation of a Undersea Medical Officer (UMO) and with the CO’s or OIC’s approval
Should you use AIR or AIR/O2 option?
- All SCUBA dives are AIR dives
- Only Surface supplied dives can deliver 100% O2
- 100% O2 allows divers to off gas quicker due to lack of N2
Table and Schedule Format; For No D Dive
EX. 43 fsw, BT :40
T/S_45/:46, No D, F
Table and Schedule Format for Decompression Dive
EX. LS 0900, Depth 85’, BT :34
T/S_90/:35, AIR D, :04 STOP @ 20’, J
LS
Left Surface
RB
Reached Bottom
LB
Left Bottom
R
Reached Stop
L
Left a Stop
RS
Reached Surface
TBT
Total Bottom Time
TDT
Total Decompression Time
TTD
Total Time of Dive
Variations in Rate of Ascent
- Do not ascend faster than your SMALLEST BUBBLES
- If ascending faster than 30 fpm, Stop the ascent and allow watches to catch up
- Disregard delays of 1 minute or less
Delays Deeper than 50’
- Round delay up to nearest whole minute and add to the BOTTOM TIME
- Use new decompression schedule, based off new bottom time
Delay Shallower than 50’
No D Dive
-Delay is accounted for in the ASCENT TIME
Decompression Dive
-Delay is rounded up to the next whole minute and added to the 1st decompression stop
Repetitive Diving Terms
Repetitive Dive (repet) -Any dive conducted while N2 is still present in the body from a previous dive Repetitive Group Designator -Ex. "K" "I" "J" -closer to "Z" more N2 in body
Surface Interval
-Time a diver has been on surface following a dive
-Begins as soon as diver surfaces
-Ends as soon as descent for next dive begins
RS - LS = Surface Interval
Residual Nitrogen
- N2 that is still in divers tissues after surfacing from a dive
Residual Nitrogen Time
(RNT)
- Time (minutes) added to the bottom time of repet dive to compensate for nitrogen still in solution in divers body
Equivalent Single Dive Time
(ESDT)
- Time in minutes for which a repet dive is selected
- RNT + BT = ESDT
If surface interval is less than 10 minutes what is the procedure?
Add bottom times together and use the decompression table for the deeper of the two dive depths
RNT Exception Rule
- Occurs when surface interval (SI) between dives is short
- Recalculate the RNT requirement by summing the 2 bottom times and using the deepest depth
- Compare to the RNT table/schedule and choose the one with the lesser decompression obligation
- AKA “Alternative Method”
Diving at Altitude
Due to reduced atmospheric pressure dives at altitude require MORE decompression than identical dives at sea level
Sea Level Equivalent Depth
(SLED)
-Gives corrected sea level equivalent depths and equivalent depth stops for dives 10-190 fsw and for altitudes 1000-10000 ft
NAVSEA 00C
Big bosses
Call if there are any questions not covered
“specific guidance”
Altitude Correction Requirements
0-300 ft = No correction
300 - 1000 ft = Correct dives deeper than 145
1000 - 10000 ft = Correct all dives
>10000 = Call NAVSEA 00C
Flying after Diving
- Ascent to altitude after diving increases risk of DCS
- More “fizz” is released due to lowered atmospheric pressure
- Determine SI needed by taking the “highest” repet dive group designator achieved in past 24 hours
- Commercial flights = 8000 ft
- If flying below the altitude where a dive was conducted no SI is required
