Navy Dive Table Lecture

History of Dive Tables Theory Definition of Half Time Half Times Vary Between Tissues Supersaturation Evolution of Recreational Dive Tables Use of Dive Tables Examples Navy Dive Tables

From Scuba Diving Explained by Lawrence Martin

http://www.mtsinai.org/pulmonary/books/scuba/index.html

History of Dive Tables

Decompression sickness became prevalent in mining and bridge building industry.

Elevator story, fast ascension resulting in bent bridge builders.

Paul Bert (French) late 1800's encouraged slow decompression to prevent symptoms of caisson disease. No quantitative results given

John Scott Haldan 1906-1908 performed experiments on 85 goats.

• Symptoms began to occur when decompression of ambient pressure was greater than one half. 4 atm -> 2 atm.
• Symptoms showed that the goats felt uneasy in one or more of its legs, they would hold the leg in the air not placing any weight on it.

Theory

Haldane believed absorption and elimination of nitrogen was an exponential process.

Definition of Half Time

Half Time = the amount of time it takes for a tissue to absorb/release half the partial pressure difference.

Since N₂ make 80% of the air, pN₂ @ sea level is 0.80 x 1 atm = 0.80 atm.

Partial pressure from 1 atm to 4 atm is

4 x 0.80 atm - 0.80 atm = 2.40 atm.

Half Time would be the amount of time to reach

0.80 atm + 1/2(2.40 atm) = 2.00 atm.

Partial Pressure for 20 minute Half Time, from 1 atm(surface) to 4 atm (99 ft)

# of Half Times	Total Duration [min]	% of N2 Saturation	pN2 in tissue [atm]
0	0	0	0.80
1	20	50	2.00
2	40	75	2.60
3	60	87.5	2.90
4	80	93.75	3.05
5	100	96.875	3.125
6	120	98.5	3.164
¥	¥	100	3.20

Partial Pressure for 20 minute Half Time, from 4 atm (99 ft) to 2 atm(33 ft)

# of Half Times	Total Duration [min]	% of N2 Saturation	pN2 in tissue [atm]
0	0	0	3.20
1	20	50	2.40
2	40	75	2.00
3	60	87.5	1.80

Half Times Vary Between Tissues

• Fat tissues are slow at absorbing/eliminating N₂ (HT in hours)
• Nerve tissues, like the brain are fast (HT in minutes)
• Blood in the lungs are the fastest transferring N₂ almost instantly (fraction of a second)

Supersaturation

As the diver ascends, tissues are supersaturated with N₂. N₂ is released from the tissues into the blood.

Around 2x pN₂ difference, N₂ is not able to dissolve in the blood, bubbles form.

Very small bubbles may be OK, as they increase in size they can block blood vessels causing pain and damage.

Evolution of Recreational Dive Tables

Haldane's tables were adopted first by the British Navy,

1915 - U.S. Navy adopts Haldane's tables.

1930 - U.S. Navy modified the tables after running additional tests on sailors.

1980 - The tables were standardized for recreational scuba diving

Modifications were required:

It was found that a safe ratio of decompression pressure was not 2:1 but 1.5:1.

Therefore limits were placed on diving below 33 ft.

No dive table is 100% safe.

Navy tables were design with some inherent risk, no risk would make deep diving unavailable, and navy has use of hyperbaric chambers.

NAUI tables are derived from the Navy tables with additional safety factors.

Breathing rates, body exertion, which are affected by, stress, temperature, age, weight, and many other factors make the tables less consistent.

Use of Dive Tables

Navy Dive tables are based on a square wave

ABT = Actual Bottom Time

SIT = Surface Interval Time

RNT = Residual Nitrogen Time

EBT = Equivalent Bottom Time

MBT = Maximum Bottom Time

Single dives can use the maximum decompression limits

Depth [ft]	No-Decompression Limits [min]
35	310
40	200
50	100
60	60
70	50
80	40
90	30
100	25
110	20
120	15
130	10

Repetitive Dive (multiple dives within a 12 hour period) uses Repetitive Group Designation

Dive tables are good for both fresh and salt water.

Not good at higher altitudes

Should wait 24 hours before flying

Should always give a 5 minute safety margin

If in cold water or exerting heavy work add 10 ft. to depth

Examples

Items in parenthesis are derived from dive tables using the previous given information.

(1) No Decompression Limit For 60'	(2) 5 hour dive at SSL

(3) Huntsville Triple Dive

(4) Plan Deeper Dives First

(5) Original Dive times would produce a decompression dive

(6) Decompression Dive

Navy Dive Tables