Pressure

1. Pressure Pressure-Volume Relationship Boyle’s Law

2. Objectives • Compare and contrast Atmospheric Pressure, Hydrostatic Pressure and Ambient Pressure. • Correctly complete a chart showing the relationship between pressure and volume. • Correctly calculate air consumption rates for various depths. • Define squeeze. • Identify the commons sites of squeeze in a diver. • Describe various methods for preventing squeeze.

3. Pressure • Force per unit area • Pounds per square inch (PSI

4. Atmoshperic Pressure Pressure exerted by the atmosphere above you • 1 atmoshpere (atm) = 14.7 psi • Column of air 1 inch square 100 miles high

5. Hydrostatic Pressure • Pressure generated by the column of water above you • 33 feet of seawater (FSW) = 1 atmosphere • 34 feet of freshwater (FFW) = 1 atmoshpere

6. Ambient Pressure • Ambient pressure is the pressure surrounding you. • This is the pressure that affects you while you are diving. Ambient Pressure = Atmospheric Pressure + Hydrostatic Pressure

7. 0 1 1 1 33 2 2 1/2 66 3 3 1/3 99 4 4 1/4 132 5 5 1/5 FSW Patm Density Vol ft3

8. 0 1 1 1 33 2 2 1/2 66 3 3 1/3 99 4 4 1/4 132 5 5 1/5 FSW Patm Density Vol ft3

9. 0 1 1 33 2 1/2 66 3 1/3 99 4 1/4 132 5 1/5 25 psi/min 120min 50 psi/min 60 min 75 psi/min 40min 100 psi/min 30 min 125 psi/min 24 min FSW Patm Vol ft3

10. Squeeze Objectives • Define squeeze and state the cause. • List 4 air spaces of a diver that are subject to squeeze, and describe the golden rule for squeeze prevention. • Name and describe one technique for equalizing pressure in the middle ear. • Identify the general category of injuries that are most common in scuba diving. • Identify the cause for reverse block, at what point during a dive reverse block might occur, and explain one technique for dealing with a reverse block. • Describe one incorrect method for dealing with a reverse block.

11. Definition • Pain due to pressure imbalance between diver air spaces and ambient pressure Cause • Diver fails to anticipate and properly equalize pressure imbalance which results from change in depth

12. Golden Rule: • Equalize before you feel any discomfort. • If you experience any pain or discomfort, • reverse direction until the pain is relieved, • Equalize • resume the ascent or descent as appropriate. • Descents should be performed • feet first through the first 10-15 feet • slowly to allow time to equalize.

13. Common Sites of Squeeze

14. Ear Squeeze Indications Discomfort or Pain in ear Remedy Ascend until pain or discomfort is relieved Prevention Equalize early and often Before experiencing discomfort or pain Valsalva technique

15. Mask Squeeze Indications Mask sucking in against your face Remedy Exhale into your mask Mask must cover your nose Prevention Exhale into your mask Mask must cover your nose

16. Sinus Squeeze Indication Pain in sinus Blood in your mask Remedy End the dive Prevention Dive when healthy Medications?

17. Hood Squeeze Indications Unable to equalize ears Feel hood push into your ear Remedy Pull hood away from your head to allow water to enter Prevention Allow water into your hood before descent

18. Tooth Squeeze Indications Pain in jaw Remedy End dive Prevention Automatic if healthy May be confused with sinus squeeze

19. Reverse Block Indications Pain on ascent Remedy Re-descend if time and air allow Ascend slowly Wiggle jaw Prevention Automatic if healthy

20. Summary Boyle identified the relationship between pressure and volume Affects Buoyancy Air consumption Squeeze anticipate and equalize early and often