AAUS Test Review & Diving Physics By Carlie Williams SCUBAnauts International Tarpon Springs Chapter
What is AAUS? • The American Academy of Underwater Sciences • Organized in 1977 to establish standards and operating procedures for scientific diving. • AAUS is an organization of organizations that participate in scientific diving. • Research institutions • Universities • Consulting companies • Comprised of ~4000 individuals in the USA. • Most are career scientific divers • 25% women
AAUS Requirements • SCUBA Certification • Swimming Evaluation • Skin Diving Evaluation • Medical Exam • Written Exam • CPR, 1st Aid, O2 training • 12 Training Dives Maintenance of Certification • 1 logged dive every 6 months • 12 logged dives per year • Current CPR, 1st Aid and O2 • Up-to-date medical records Each AAUS organizational member (ex. SNI) is required to certify it’s scientific divers to the AAUS Level.
“As an organizational member of AAUS, all SNI divers must comply with AAUS standards for scientific diver qualifications.” –SCUBAnautInternational, Inc. Standard Operating Procedures
Pressure & Diving What is pressure? Force per unit area applied to an object. Is there pressure acting upon our bodies right now? How much? Where is it coming from? At sea level, the mass of the atmosphere exerts 14.7 pounds per square inch (psi) or 1 ata of pressure on us all the time. What happens when we go underwater? The mass of the water above us will increase the pressure exerted on our bodies and the gases we breathe.
For every 33 ft (10 meters) increase in seawater depth, pressure increases by 1 ata. • Absolute Pressure: Total pressure exerted on diver and gases. • At Sea level: 1 ata • At 33 ft: 2 ata (1 ata@ SL + 1 ata @ 33ft) • At 99 ft: ??? • Gauge Pressure: Ignores the 1 ata at sea level and is only a function of depth. • At 33 ft: 1 ata • At 20 meters: ???
Absolute Pressure Gauge Pressure 1ata 0 ata 33 ft 66 ft 99 ft 30 m 20 m 10 m 1ata 2 ata 2 ata 3 ata 3 ata 4 ata Sea Level
Diving & Pressure Examples 1. What is the absolute pressure in atmospheres (ata) at 60 feet? • How to solve i. We know 1 ata = 33 feet ii. Absolute Pressure = [Depth in feet ÷ 33] + 1 ata Absolute Pressure = [60 ÷ 33] + 1 = [1.82] + 1 Absolute Pressure = 2.82 ata
Seawater vs. Freshwater 1 ata = 14.7 psi (pounds per square inch) In seawater: 1 ata of pressure = 33 ft depth in seawater 1 ft3 of seawater = 64 lbs In Freshwater: 1 ata of pressure = 34 ft depth 1 ft3 of freshwater = 62.4 lbs
Important Gas Laws Boyle’s Law Henry’s Law Dalton’s Law
Boyle’s Law 3 3 Volume and pressure of gases are inversely proportional. P1V1 = P2V2 As pressure increases, gas volume decreases Real-life scenario: A diver at 66 feet below sea level is under _____ times the amount of pressure then at the surface. This means that his/her regulator must provide ____ times the amount of gas to the diver’s lungs.
Boyle’s Law examples: 2. A sealed balloon filled with air has a volume of 6 cubic inches at sea level. What is the volume of the balloon at 66 ft seawater? • How to solve • Use Boyle’s Law Equation P1V1 = P2V2 P1 = 1 ata P2 = 3 ata V1 = 6 inches3 V2 = ??? (1 ata) x (6 inches3) = (3 ata) x (V2) 6 = 3V2 V2 = 2 inches3
Boyle’s Law (cont) • A diver at 33 feet seawater breathes in 180 inches3 of air from his/her regulator. By how much would that air expand in the diver’s lungs if they did not exhale? • How to solve • Use Boyle’s Law Equation P1V1 = P2V2 P1 = 2 ata P2 = 1 ata V1 = 180 inches3 V2 = ??? (2 ata) x (180 inches3) = (1 ata) x (V2) 360 = 1V2 V2 = 360 inches3 The air in the diver’s lungs would double in volume if they did not exhale as they ascended.
Boyle’s Law & Diving Safety • During Descents: • “Squeezes” • Ear • Sinus • Tooth • Mask • During Ascents: • Over Expansion Injuries • Air Embolism • Lung Ruptures • Why do diver’s need to be aware of Boyle’s Law? • Barotrama • “Baro” means pressure • “Trama” means injury
Henry’s Law The amount of gas dissolved in a given volume of a liquid is proportional to the partial pressures of the gas in equilibrium with the liquid. As absolute pressure increases, partial pressures of gases also increase. The volume of air we breathe underwater is the same, but the gas is more dense. We breathe more molecules of the gas as we go deeper.
Dalton’s Law • The total pressure of a gaseous mixture is equal to the sum of each individual component. • PTotal = P1 + P2 + P3 + … • What gases make up air? • 78% Nitrogen, 21% Oxygen, 1% Other • We already know how to calculate the absolute (total) pressure of a gaseous mixture (ex. Air, Nitrox) at any depth (using Boyle’s Law). • With Dalton’s Law we can calculate the partial pressures of each gas.
Dalton’s Law Examples • 4. What is the partial pressure of oxygen in air at sea level in psi (pounds per square inch)? • How to solve • i. What is the absolute pressure of air at sea level? • 1 ata • ii. What % of air is made up of Oxygen? • 21% -or- 0.21 in decimal form Partial Pressure of a gas = (% gas in decimal form) x (absolute pressure) • iii. Partial Pressure of O2 = (0.21) x (absolute pressure) PO2 = 0.21 x 1 ata PO2= 0.21 ata
Dalton’s Law (cont) • 5. What is the partial pressure of oxygen in air at 99 ft in psi (pounds per square inch)? • How to solve • i. What is the absolute pressure of air at 99 ft? • 4 ata • ii. Air = 21% Oxygen (0.21 in decimal form) Partial Pressure of a gas = (% gas in decimal form) x (absolute pressure) • iii. Partial Pressure of O2 = (0.21) x (absolute pressure) PO2 = 0.21 x 4 ata PO2= 0.84 ata
Air Consumption • Effected by level of activity, temperature, stress and water depth. • How does water depth effect air consumption? • As you go deeper, gases will decrease in volume (Boyle’s Law) so there is less available. However, volume of air in each breath you take does not change. This means you use more more air at greater depths.
Calculating your Air Consumption Diver 1 breathes 600 psi in 5 minutes at 33 feet seawater. Diver 2 breathes 1200 psi in 7 minutes at 45 feet seawater. Which diver has a better air consumption rate? We know that as depth and absolute pressure increases, air consumption rates should also increase. Solution: Calculate the Surface Air Consumption (SAC) Rate. The SAC rate what the air consumption rate would be if the diver was at the surface.
Surface Air Consumption (SAC) Rate • 6. Diver 1 breathes 600 psi in 5 minutes at 33 feet seawater. • How to solve i. Calculate diver’s air consumption at depth (DAC) 600 psi/5 minutes = 120 psi/minute ii. Calculate absolute pressure of diver’s gases 33 ft seawater = 2 ata iii. Calculate SAC SAC = DAC ÷ absolute pressure SAC = 120 ÷ 2 SAC = 60 psi/minute
Surface Air Consumption (SAC) Rate • 7. Diver 2 breathes 1200 psi in 7 minutes at 60 feet seawater. • How to solve i. Calculate diver’s air consumption at depth (DAC) 1200 psi/7 minutes = 171 psi/minute ii. Calculate absolute pressure of diver’s gases 66 ft= 3 ata iii. Calculate SAC SAC = DAC ÷ absolute pressure SAC = 171 ÷ 3 SAC = 57 psi/minute
Surface Air Consumption (SAC) Rate • 8. Diver 3 has a SAC of 30 psi/minute. What would their DAC rate be at 33 ft seawater? • How to solve i. Calculate absolute pressure of diver’s gases 33 ft = 2 ata ii. Calculate diver’s air consumption at depth (DAC) DAC = SAC x absolute pressure DAC = (30 psi/minute) x 2 ata DAC = 60 psi/minute
Other Topics to Review: • Physical Parameters of Seawater: • How do sound and light waves behave in water? Air? • Dive Equipment: • What does each piece of equipment do? • Regulators: • 1stStage, 2nd Stage, Primary, Alternate, etc. • Many different types of regulators and cylinder valves • How to properly clean, service/inspect and store • SCUBA tanks • Personal Equipment
The AAUS test will be administered at the February Dry Meeting (February 9th, 2012). You will need to schedule a time to take the test before you dive if you will not be at the February meeting. You will pass this test! …if you… - Review your open-water book - Know how to solve the practice problems - Study the “Other Topics” listed