Depth and Time Limits for Scuba Divers

1
Depth and Time Limitsfor Scuba Divers

• Objectives
• To learn that there are Depth and Time Limits for
  Scuba Diving
• To Understand Why the Limits Exist
• To Learn to Safely Stay within the Limits
• To Learn to Recognize the Effects of Exceeding
  the Limits
• To Learn the Procedures for Assisting a Diver
  that has Exceeded the Limits

2
Partial Pressures

• Daltons Law- the total pressure of a gas mixture
  equals the sum of the partial pressures that make
  up that gas mixture.
• In air at sea level (one Atmosphere) 78 of the
  pressure is due to N2, 21 is due to O2
• As depth increases, the pressure also increases,
  but the relative partial pressures stay the same

3
Nitrogen Narcosis

• N2 is ordinarily an inert (inactive) gas
• Under pressure N2 has an intoxicating effect
• For most divers, the effects will be noticed at
  depths slightly greater than 100 feet
• Some divers will feel the effects as shallow as
  40 feet

4
Nitrogen Narcosis-Martinis Law

• For most divers, descending 50 feet is like
  having a dry Martini.
• Most people can handle 1 or 2
• At 100 feet it is like having 2 Martinis
• At 150 feet it is like having 3
• At 200 feet it is like having 4
• At 250 feet the diver becomes a menace to himself
  and anyone near

5
Oxygen Toxicity

• Scuba divers never breath pure O2 below 20 feet
• O2 toxicity occurs when the partial pressure is lt
  1.6 ATA
• This occurs with pure O2 at 20 feet or with
  regular air at 250 feet
• Divers that suffer from O2 toxicity usually drown

6
Decompression Sickness-the Bends Causes

• Henrys Law-gas will dissolve in a liquid in
  direct proportion to the pressure on the gas
• As you know, nitrogen makes up 78 of the air you
  breathe
• As one dives deeper, there is more pressure,
  gases, especially N2, dissolve in the blood in
  greater quantities than normal

7
Decompression Sickness-Causes

• There are limits to how much gas can be dissolved
  at any given pressure
• Saturation occurs when this limit is reached
• As pressure increases, the saturation limit
  increases
• As long as the pressure remains constant, there
  is no problem

8
Decompression Sickness-Causes

• When pressure is reduced, as in ascent, the
  saturation limit is also reduced
• Not as much N2 can be dissolved
• As pressure decreases, the N2 begins to come out
  of solution as bubbles
• The bubbles then accumulate forming bigger
  bubbles and collect in the joints, in blood
  vessels and around nerves

9
Decompression Sickness-Symptoms-what you feel

• Skin itch.
• Joint or limb pain.
• Unusual fatigue.
• Numbness, tingling.
• Abnormal sensations.
• Chest or abdominal pain.
• Deafness or ringing in the ears.
• Bladder or bowel incontinence.
• Headache, dizziness or nausea.

10
Decompression Sickness-Signs-what someone else
sees

• Skin rash.
• Weakness.
• Paralysis.
• Staggering.
• Personality change.
• Unequal pupil size.
• Slurred speech.
• Coughing or shortness of breath.
• Collapse or unconsciousness.

11
Decompression Sickness-Factors that affect

• Most important factors are depth and time.
• Rapid ascent .
• Repetitive diving and improper use of dive tables
  or computers.
• Diving deeper than 80 feet.
• Lack of sleep.
• General fatigue.
• Use of alcohol and hangover.
• Dehydration.
• Illnesses affecting the circulatory or
  respiratory systems.

12
Decompression Sickness-Treatment

• Requires recompression as soon as possible.
• Stabilization and prompt medical treatment for
  life threatening injuries.
• Early recompression therapy is most effective.
• Immediate Oxygen first aid is vital
• Helps remove N2 from tissues.
• Increases O2 to tissues.
• No in-water recompression.
• Results in additional N2 uptake.
• Symptoms worsen.
• Communication problems.
• Cold and insufficient air problems.

13
Decompression Sickness-Prevention

• Use dive tables and dive computers
  conservatively.
• Never exceed the no-decompression limits.
• Dive tables should be consulted for repetitive
  dives and must be kept within no-decompression
  limits.
• Best means of prevention.
• Plan your dive,
• Dive your plan.

14
Decompression SicknessReview

• Daltons Law of Partial Pressures.
• Nitrogen Narcosis.
• Martinis Law.
• Oxygen toxicity.
• Decompression Sickness.
• Henrys Law.
• Causes
• Symptoms.
• Signs
• Treatment.
• Prevention