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Air Consumption

Air Consumption. Learning Objectives:. Correctly calculate the surface air consumption rate in either psi/min. or ft 3 /min. given: depth, time at depth, and amount of air used. Correctly calculate the air consumption rate for any depth, given the consumption rate for any other depth.

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Air Consumption

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  1. Air Consumption

  2. Learning Objectives: • Correctly calculate the surface air consumption rate in either psi/min. or ft3/min. given: depth, time at depth, and amount of air used. • Correctly calculate the air consumption rate for any depth, given the consumption rate for any other depth. • Correctly calculate air consumption when the size of the cylinder used is changed.

  3. Main Points • Calculating gas consumption rates at the surface and at depth. • Converting surface consumption rates (SCR) to depth consumption rates (DCR). • Converting depth consumption rates (DCR) to surface consumption rates (SCR). • Converting gas consumption rates from psi/minute to cu. ft./minute • Converting gas consumption rates from cu. ft./minutes to psi/minute

  4. Calculating Gas Consumption Rate at Depth (DCR) Calculate gas consumption rate at depth using the following formula • Gas used/ time Example: A diver at 66' in the ocean breathes 750 psi in 10 minutes. What is the divers air consumption rate at depth (DCR)? Answer: 750 psi / 10 minutes = 75 psi per minute @ 66' S.W.

  5. Converting DCR to Surface Gas Consumption Rate (SCR) Convert a DCR to SCR using the following Formula: DCR / Pressure atm Remember the formula for converting depth to pressure is Seawater Patm = (depth + 33) / 33 Freshwater Patm = (depth + 34) / 34

  6. Example 1 If a diver has a DCR of 75 psi/minute at a depth of 66 fsw, what is that diver’s SCR? Answer: DCR / Patm 75 psi per minute /[(66 + 33)/33)] 75 psi per minute / 3 atm 25 psi per minute @ The Surface

  7. Converting SCR to DCR When converting a SCR to a DCR use the following formula: DCR = SCR x Pressure

  8. Example A diver has a known SAC of 25 psi per minute @ the surface. What is that diver's DCR @ 78 fsw? Answer: DCR = 25 psi per min. x [(78+33)/33] DCR = 25 psi per min. x 111 / 33 DCR = 25 psi per min. x 3.4 DCR = 85 psi per min. @ 78 fsw.

  9. Converting consumption Rates from psi/minute to cu ft/minute Example: A diver has a known SCR of 25 psi/minute using an Al. 80. What is the diver's SCR in cubic feet per minute? Answer: Determine ft3 / psi 80 ft3 / 3000 psi = .027 ft3 / psi SCR psi/min x ft3 / psi (25 psi/minute) x (.027 ft3 / psi ) = .675 ft3 / minute

  10. Check your answer • 3000 psi / 25 psi min = 120 minutes • 80 ft3 / .675 ft3/minute = 118.5 minutes

  11. Converting from psi/min to cu ft/min and from SCR to DCR A diver, using an Al. 80 filled to 3000 psi. has a known SCR of 20 psi/minute. In ft3/min, What is the diver’s breathing rate, @ 57 fsw?

  12. Converting from psi/min to cu ft/min and from SCR to DCR continued Step 1 Convert the SCR from psi/min to ft3 /min 80 ft3/3000 psi = .027 ft3/psi .027 ft3/psi x 20 psi/min = .54 ft3 / min Step 2 Convert SCR to DCR .54 ft3/min. x[( 57 + 33)/33] .54 ft3/min. x 2.7 DCR = 1.46 ft3/min. @ 57 feet SW

  13. Converting from ft3/minute to psi/minute When converting from ft3/min to psi/min first determine how many psi/ft3 Formula Psi when full / ft3 when full 3000 psi/63 = 47.62 psi/ft3

  14. Converting from ft3/minute to psi/minute A diver using an AL 63 filled to 3000psi has a known SCR of .55 ft3/min. Using the same cylinder, what is the diver’s SCR in psi/min. Answer: Determine psi/ft3 3000 psi / 63ft3 = 47.62 psi/ft3 Multiply known SCR x psi/cu ft SCR = .55 ft3/min x 47.6 psi/ft3 = 26.18 psi/min

  15. Converting from ft3 /min to psi / minConverting DCR to SCR A diver using an AL 63 filled to 3000psi has a known DCR of.8 ft3/min at 27ffw. Using the same cylinder, what is the diver’s SCR in psi/min.

  16. Step 1 Convert from ft3 / min to psi / min 3000 psi / 63 ft3 = 47.62 psi / ft3 .8 ft3 / min x 47.62 psi / ft3 = 38.1 psi / min @ 27ffw Step 2 Convert DCR to SCR 38.1 psi / min / (27ffw + 34ffw)/34ffw 38.1 psi / min / 1.79 atm = 21.28 psi / min SCR

  17. Converting air consumption rates and tank sizes • Convert Consumption Rate to to ft3/min • Determine ft3/psi for new cylinder • Determine psi/min for new tank size Example A diver has a known SCR of 25 psi/min using AL 80. What is the SCR using an Al 63? Answer 80 ft3 / 3000 psi = .027 ft3 /psi x 25 psi/minute = .675 ft3/min Psi/FT3 for AL 63 = 3000 psi/63 ft3 = 47.6 psi/ft3 47.6 psi / ft3 x .675 ft3 / minute = 32 psi/minute

  18. Have We Covered • Calculating gas consumption rates at the surface and at depth. • Converting surface consumption rates (SCR) to depth consumption rates (DCR). • Converting depth consumption rates (DCR) to surface consumption rates (SCR). • Converting gas consumption rates from psi/minute to cu. ft./minute • Converting gas consumption rates from cu. ft./minutes to psi/minute

  19. Can You • Correctly calculate the surface air consumption rate in either psi/min. or ft3/min. given: depth, time at depth, and amount of air used? • Correctly calculate the air consumption rate for any depth, given the consumption rate for any other depth? • Correctly calculate air consumption when the size of the cylinder used is changed?

  20. Last Thoughts • Most divers have a good intuitive understanding/guesstimate of how much bottom time they can get based on cylinder size, depth and exertion level. • As you get into advanced diving activities it is important to have a more accurate understanding of your gas consumption rates and gas supply requirements. • Knowing our gas consumption rates in cu. ft./minute allows you to select the appropriate size cylinder for the task.

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