Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
25 Cards in this Set
- Front
- Back
|
What are the four parts of the Haldane Decompression Model?
|
(1) Compartments absorb gas at varying rates;
(2) At depth N2 pressure is higher than in air due to increased partial pressures, so is absorbed by body; (3) Eventually the tissue will saturate; (4) On ascent, body's N2 pressure is greater than ambient partial pressure so will begin to offgas. |
|
|
What is a halftime in diving?
|
The length of time it takes to reach halfway between current pressure and saturation.
For example, a 20 minute compartment has a halftime of 10 minutes. It will reach half-saturation after 10 minutes, and in a second halftime will reach 3/4 saturation (1/2 + 1/4). |
|
|
When is saturation reached at depth in the Haldane model?
|
Six halftimes. For example, a 10 minute compartment saturates in 60 minutes.
|
|
|
What is the condition called after six halftimes have elapsed at depth?
|
Saturation.
|
|
|
What is tissue pressure?
|
The theoretical depth a tissue has absorbed to.
For example, a 5 minute compartment at 60 feet after 10 minutes will have absorbed 2 halftimes (30 for the first, 15 for the second), for a tissue pressure of 45 feet. |
|
|
What is a pressure gradient?
|
The difference between tissue pressure and gas partial pressure. Zero at saturation.
|
|
|
What is an M-Value?
|
The maximum tissue pressure (expressed in depth, fsw) a compartment may have so as not to exceed a maximum pressure gradient during no-decompression diving.
Fast compartments have higher M-values. During a dive, when any compartment hits its M-value, the dive ends. |
|
|
What determines the maximum time at a particular depth?
|
When a compartment hits its M-value, called the controlling compartment.
Example: if a fast (5-minute) compartment has an M-value of 60 fsw, then the maximum no-stop dive time at 120 feet is 5 minutes (one halftime, ½ * 120 = 60). But at 50 feet, even at saturation (6 * 5 = 30 minutes) the M-value cannot be reached - saturation is 50 fsw. So a slower compartment must control that dive. |
|
|
If a compartment is a 20 minute compartment, what is it's tissue pressure after 60 minutes at 40 feet?
|
35 feet.
60 minutes is 3 halftimes. The first halftime is 20 feet, the second is 10 feet more, the third adds 5 feet. |
|
|
What are three models of surface interval credit?
|
EE - Exponential/Exponential - offgassed at compartment rate, e.g., a 5-minute compartment is clean in 6 8 5 = 30 minutes
US Navy - 120 minute washout for all compartments - 6 * 120 = 12 hours for clean PADI RDP - 60 minute washout for all compartments - 6 * 60 = 6 hours for clean |
|
|
What are Spencer Limits?
|
New RDP M-values developed by Dr. Rogers in 1987.
|
|
|
What are Bühlmann Limits? What are their relationship to Spencer Limits?
|
Even lower M-values than Spencer Limits.
|
|
|
How did Paul Bert contribute to the development of decompression theory?
|
He determined that dissolved N causes DCS
|
|
|
How did John Scott Haldane contribute to the development of decompression theory?
|
He created the Haldane model, and the Haldane decompression tables (1908)
|
|
|
How did the US Navy update Haldane's tables?
|
Updated compartment model
Used 120 minute halftimes Tested tables on divers |
|
|
How did Dr. Raymond Rogers contribute to the development of decompression theory?
|
Used doppler ultrasound flow meters to lower M-values,
Changed to 60-minute surface interval credit Used 14 compartments ranging from 5 to 480 minutes |
|
|
How do you alter RDP use in cold water or in strenuous conditions?
|
Add 10' to depth calculations
|
|
|
What are the suggested depth limits?
|
Scuba Divers - 40 feet
OW Divers - 60 feet Experienced/Deep Divers - 100 feet Max 130' for all divers |
|
|
What do you do if you exceed a table limit by less than 5 minutes?
|
Immediately ascend slowly to 15 feet
Mandatory 8 minutes safety stop Don't dive for 6 hours |
|
|
What happens if you hit pressure group W or X?
|
Minimum surface interval of 1 hour
|
|
|
What happens if you hit pressure group Y or Z?
|
Minimum surface interval of 3 hours
|
|
|
When are safety stops mandatory?
|
Diving to 100' or more
Within 3 PG of No Decompression Limits When you hit any NDL (depth, time) |
|
|
What are the rules for flying after diving?
|
One dive - no flying for 12 hours
Multiple dives - 18 hours Decompression diving - 24 hours suggested |
|
|
What is the flying after diving rule for a single dive day?
|
No flying for 12 hours
|
|
|
What is the flying after diving rule for a multiple dive day?
|
No flying for 18 hours
|
