1. PADI Section 4
Breathing Air at Depth

2. The Air you Breath
Air is a mix of 79% nitrogen, 21% oxygen and less than 1% of a dozen other gases.
Depth, pressure, volume, density relationships apply as if air was a single gas and to breathing gases other than air
Enriched air nitrox has the same gases as air but different proportions, 22% or more oxygen
PADI enriched air Diver course certifies you in nitrox use ,

3. Composition of Air

4. Gas Laws

5. The Air you Breath
We need oxygen to live, but it is toxic to us at high pressures
The higher the oxygen content the shallower the limit for using it
Nitrox allows us to dive longer at shallower depths with special Nitrox Tables
To avoid oxygen toxicity when diving with air do not exceed 130 ft maximum depth
The limit for using pure oxygen is 20 ft for decompression purposes
Recreational divers do not use pure Oxygen but Tec divers often do

6. Contaminated Air
Contaminated Air contains unintended impurities and is very rare in diving
Contaminates may be harmless at the surface but toxic at depth
Compressors for filling SCUBA cylinders use special filters and separators
Contaminated air may smell and taste bad but sometimes can be odorless and tasteless

7. Contaminated Air Possible Causes of contaminated air are:
Filling a cylinder at an improper source
Improper maintenance of filling system
Very high levels of contaminates in the source gas
A diver breathing contaminated air may have these symptoms- Headache, dizziness, Nausea, unconsciousness, cherry red lips/ nail beds

8. Contaminated Air
If you suspect a diver has breathed contaminated air have them breath fresh air, give emergency oxygen and perform CPR if necessary
Contact Emergency medical care and seek medical attention
Have your Diving cylinders filled at professional dive operations who have been inspected and certified as clean/ pure air

9. Decompression Sickness
Time underwater has limits as to how much nitrogen gas is in solution in your body
With greater depth and more time your body absorbs more nitrogen
While ascending and on the surface your body gets rid of excess nitrogen when exhaling over several hours
If nitrogen levels in your body are too high when you ascend nitrogen bubbles can form in your blood and tissues, also known as the “Bends”

10. Decompression Sickness
Nitrogen Bubbles forming in your tissues is a serious medical condition, symptoms include: Paralysis, numbness, tingling, joint and limb pain, shock, Difficulty breathing, weakness and fatigue, and in severe cases unconsciousness and death
Symptoms usually occur 15 minutes to 12 hours after a dive, but can occur during a dive or after 12 hours
Symptoms can be moderate or severe, treat all cases of suspected DCS with medical attention

11. Decompression Sickness
Secondary Factors which can affect how much nitrogen is absorbed and released by the body leading to decompression sickness include: Fatigue, cold, illness, dehydration, Injuries, Age, Poor fitness, Alcohol consumption and strenuous activity during a dive
On a very cold or strenuous Dive you breath at a higher rate and absorb more Nitrogen, count the dive as if it were 10 ft deeper for additional safety

12. Dive Tables and Dive Computers
Scientists created mathematical decompression models to estimate how much nitrogen a diver has in their body
Dive time and depth information is used to calculate the amount of nitrogen absorbed
A Dive computer constantly updates information as depth changes
There is no way of measuring directly how much nitrogen is in a divers body

13. Dive Tables and Dive computers
Because of variations in people Dive Tables and Dive computers cannot guarantee that decompression sickness will never occur
Dive within the limits and slowly ascend form every dive
NO Stop Diving is planning your dive so that at any time you can swim directly to the surface ( no decompression Dives)

15. Dive Computer

16. Dive Tables and Dive Computers
No Stop times are the black boxes found at the bottom of the primary dive table columns
Your no stop time gets significantly shorter as depth increases, you also use air faster at greater depth
Dive Tables can only calculate the deepest depth for your total bottom time
Dive computers can be used prior to the dive to scroll through and plan multilevel dives for a much longer bottom time

17. Dive Profile