Is Diving Safe? SCUBA is safe, like motorcycling or sky-diving If you understand the physics and physiology diving is safe
Gas Laws and Diving Essential Question: What conditions lead to perils facing divers including the bends and embolism?
Review! How much does air weigh at sea level? What is the weight of water at 33 feet (10 meters)? What is the pressure on a divers body at 33 feet underwater?
Around the Bends What are the bends? How is decompression sickness treated?
Bends and embolism The bends result when dissolved gases (mostly nitrogen) absorbed as air is breathed under pressure are released as gas back into the bloodstream. Embolism results when gases in the lung expand during ascent and rupture lung tissue, causing air bubbles to enter the bloodstream. These conditions can happen if a diver ascends too quickly.
Law Makers Boyle: volume and pressure Charles: temperature and volume
Cartesian Diver Activity 1.Fill medicine dropper for neutral buoyancy 2.Fill soda bottle to just below top 3.Place dropper in soda bottle 4.Tighten bottle cap 5.Squeeze bottle 6.Note observations Boyles Law – When a gas is at constant temperature, there is an inverse relationship between the volume and pressure of the gas. As the volume decreases, pressure increases and as the volume increases, pressure decreases.
Pressure Can Activity 1.Add small amount of water to soda can 2.Place can on hot plate 3.When water in can boils remove can 4.Quickly invert can and place in bowl of water 5.Note your observations Charles Law – When a gas is at constant pressure, there is a positive relationship between the volume of a given mass of the gas increases and its temperature. As the temperature increases its volume increases and vice versa.
The Gas Laws Essential Questions: – What are the principles of Boyles Law and Charles Law? – How is the ideal gas law used to calculate changes in volume, pressure and temperature when one or the other variables is held constant?
The Equations Boyles Law: PV = k Charles Law: V 1 /T 1 = V 2 /T 2 Ideal Gas Law: PV = nRT – n = number of moles of gas – R = gas constant ( L·atm/mol·K) – T = temperature in Kelvin
Boyles Law: What does it look like? Volume Pressure Volume Pressure
Charles Law: What does it look like? Temperature Volume
Should divers care about the gas laws? Essential question: How do the gas laws relate to safe diving practices?
Why should divers care about Boyles Law? Divers who know Boyles Law know if pressure decreases, volume increases. A diver breathes gases under pressure. If a diver ascends too quickly pressure goes down so gases dissolved in the bloodstream increase in volume. Remember what happens when you shake a soda can? Yup. Gases start to fizz in the divers bloodstream. Not good.
Why should divers care about Charles Law? Air in a scuba tank is pressurized to about 3000 psi. What happens if the tank is heated, for example in a car on a summers day? Yup. The tank could explode. Not good. If a diver is close to a bends or embolism situation and is hypothermic, what could happen if the diver is quickly warmed up?
Safe Diving! What can divers do to avoid the bends and embolism? What is a safety stop? What is a decompression stop?
Dive Tables What are dive tables?
Items for your concept map pressure temperature volume diving depth atmospheres scuba dissolved gases nitrogen the bends embolism ascent Boyles Law Charles Law hyperbaric chamber
Why are gas laws important to divers?
Graph of Dive Table Data Bottom time at 70 feet (21.3 m)
Misinterpreting Dive Computers Dive computers help divers avoid risky situations Algorithms use depth and time data to estimate the likelihood of decompression sickness What happens if a diver cannot use the dive computer properly?
How Does Volume Decrease With Depth? Assume a pressure increase of 1.0 atm for every 10 m of depth below the surface Use Boyles Law to calculate the volume of a gas at pressure every 10 m of depth to 100 m Chart your data on graph paper
Volume Decreases With Depth
Depth vs. Volume vs. Pressure
Example Problem If a diver runs out of air at 15 meters underwater, and immediately ascends to the surface, what are the risks of an embolism? Assumptions: – Constant temperature – Lung capacity = 6 liters – Pressure increases 1.0 atmosphere for every 10.0 m of depth below the surface.
Solution Let P1, V1 and T1 = pressure, volume, and temperature respectively of the air in the divers lungs when the last underwater breath is taken. Let P2, V2 and T2 = pressure, volume, and temperature respectively of the air in the divers lungs at the surface. Since temperature is constant, use Boyles Law to calculate the increase in volume of the air in the divers lungs: P1 x V1=P2 x V2 Rearranging, V2 = (P1 x V1)/P2 – P1 (pressure at depth) = 2.5 atmospheres, since = 15/10 x 1 = = 2.5 (Note that 1 is added for the 1 atmosphere of pressure at the surface.) – V1 (initial breath underwater) = 6 L – P2 (pressure at surface) = 1 atm Therefore, V2 = (2.5 x 6)/1 = 15 L The volume of air is 15 liters at the surface. Since lung capacity is 6 liters, embolism is inevitable.
Enriched Air (Nitrox) How might divers overcome the problem of absorbing nitrogen which then turns to bubbles if the ascent is too fast? Breathing pure oxygen under pressure carries a significant risk of oxygen toxicity. Divers use enriched air (nitrox) which has a higher percentage of oxygen than air, but with a lower risk of oxygen toxicity.
Enriched Air (Nitrox)
Essential Questions What conditions lead to perils facing divers including the bends, embolism and oxygen toxicity? How do the gas laws relate to safe diving practices? What are the principles of Boyles Law and Charles Law? How is the ideal gas law used to calculate changes in volume, pressure and temperature when one or the other variables is held constant?