Oxygen-Enriched Air Larry “Harris” Taylor, Ph.D. Diving Safety Coordinator, U of Michigan © Larry P. Taylor, Ph.D. All Rights Reserved LPT Your Instructor U of MI Diving Safety Coordinator AAUS sanctioned Diving Safety Officer Internationally rated 3 - star instructor (CMAS) National Master Scuba Instructor (President’s Council) > 100 Diving Certifications > 100 Diving Publications > 1,200,000 visitors to “Diving Myths & Realities” web site Library: one of the best resources in North America Scuba Diver since 1977 Scuba Instructor since 1980 DAN Instructor since 1991 EANx Instructor since 1992 Ph.D. Biochemistry LPT Lecture is a Democracy! You control speed with your questions LPT There are no “stupid questions” ! The only “Dumb Question” is the one that is unanswered ‘cause it was not asked The “Dumbest Question” is the unasked question that could’ve solved a problem LPT Socratic Method: Asking & Answering Questions Still one of the best learning tools LPT The Water-work is Dictatorship! Do as instructed or leave the water LPT Knowledgeable, Physically Fit Divers GospelAccording to “Harris” Have More Fun! LPT Terminology LPT Terms Used to Describe Recreational Gas Mixes The following generic terms are used to describe mixtures of nitrogen and oxygen God’s Air (atmospheric air) Norm Air (atmospheric air) Normoxic Air (atmospheric air) Denitrogenated Air (DNA) Enriched Air Nitrox (EAN) EANx (where x is the percentage of oxygen in the mix) Nitrox Oxygen Enriched Air (OEA) Oxy-Air Safe Air There are two standard mixes: NOAA I: 32% Oxygen (EAN32) NOAA II: 36% Oxygen (EAN36) Nitrox term original use: NOAA habitat mix Less oxygen than air Air I II Emphasizes N2 major component Consistent with “heli-ox” LPT EANx Myths LPT Nitrox Is Safe or Nitrox is Safer Than Air Safe (according to Webster) means without risk Nothing in diving (life) is without risk EANx has significant decompression advantages But, has concerns: O2 toxicity (shallower onset than air) Time / depth limits for both N2 and O2 Proper mix determination, mixing, and analysis Additional equipment requirements Additional expense LPT Nitrox Is For Deeper Diving EANx has very stringent depth limits (mandated by oxygen concentration) Most useful in 50 – 110 fsw range (many deaths on EANx have been deeper than 60 fsw) LPT Nitrox Eliminates DCS Risk Nothing eliminates DCS risk in diving There are techniques to reduce risks, but risk never equals zero Benefits Never Infinite Risks Never Zero Risk / Benefit is an individual decision LPT Nitrox Makes DCS Treatment Impossible Divers using Air or EANx have same treatment protocols Advanced divers track oxygen exposure (OTU’s) Recreational EANx dives do not get close to standard OTU limits Even if OTU limit exceeded, medical treatment would be done LPT Nitrox Eliminates Narcosis Narcosis related to total gases on board Your body chemistry on the day you dive No documented study to validate this myth LPT Using Nitrox is Difficult There are procedures for tracking both N2 and O2 (similar to basic air diving tables) Diving is basically: inhale, exhale, repeat LPT EANx Advantages LPT Longer No-Deco-Required Diving Depth No-stop deco times (minutes) USN Air NN32 NN36 (fsw) (msw) 21% 32% 36% 50 15 100 200 310 60 18 60 100 100 70 22 50 60 60 80 25 40 50 60 90 28 30 40 50 100 31 25 30 40 110 34 20 25 30 120 37 15 25 130 40 10 20 LPT Longer No-Deco-Required Diving This is termed the “Decompression Advantage” of EANx LPT Longer Repetitive Dives Air Example Dive # 1: 90 fsw / 20 min: F One hour SIT: F > E Dive # 2: 80 fsw 17 min allowed Same Dive Using 36% O2 Dive # 1: 90 fsw / 20 min: E One hour SIT: E > D Dive # 2: 80 fsw 36 min allowed Using EANx provided 19 minutes more no-stop dive time Bottom Line: EANx allows more bottom time LPT Shorter Surface Interval Two different teams dive 30 min to 80 fsw Team 1 breathed air; Team 2 breathed EAN36 Team 1 emerges with a letter group of H Team 2 emerges with a letter group of F For a 2nd dive to 80 fsw for 30 minutes Team 2 must wait 0:53 to enter as E Team 1 must wait 6:33 to enter as A Bottom Line: EANx allows more bottom time More on-site time = more cost effective diving LPT “Safer” Table Use Use EANx on dive (within pO2 limits) Use Air table of choice will have less nitrogen on board Common Practice in the Recreational Community Lowered DCS Risk More Expensive Fills This is termed the “Physiological Advantage” of EANx LPT Divers Feel Less Fatigued After Dive The “Feel Good” Gas Appears to be a supported claim As long as there is no workload Most likely will never be rigorously studied Explained by lowered “decompression stress” O2 moved into cell used for metabolism N2 accumulates in cell N2 moves out on ascent Less N2 Less mechanical “abrasion” from gas movement LPT Air Diving is all about Nitrogen Management Oxygen Enriched Air Adds Oxygen Concerns When properly managed: Oxygen Enriched Air offers potential for extended bottom times When first introduced to recreational diving: Number of deaths in the 60 – 100 fsw range So many that diving oxygen enriched air was termed “death seeking behavior” Academics hoped recreational scuba would upgrade classes (we were wrong) This is a class in simultaneously managing nitrogen and oxygen while diving LPT Medical Matters LPT Gases in Air Oxygen: necessary for life We “burn fuel” C6H12O6 + 6 O2 6 CO2 + 6 H2O Too little oxygen (hypoxic) no life Too much oxygen (hyperoxic) toxic reactions Nitrogen: considered physiologically inert Involved in nitrogen narcosis & DCS (DCI) Dilutes oxygen in air; limits combustion Others Most not considered in this class … assumed part of nitrogen component LPT Air as a Breathing Mix Air: Relatively inexpensive Commonly available Most common underwater breathing mix But, N2 causes problems at deeper depths: Decompression Sickness Nitrogen Narcosis LPT Nitrogen Narcosis Narcosis: Pronounced “anesthetic effect” Observed when breathing N2 containing mixes at depth Deeper the depth, more intense the effect So-called Martini’s Law: (Not considered valid) Every ~50 fsw of depth = 1 dry martini on an empty stomach LPT Many Gases Have a Narcotic Potency Meyer-Overton Theory of Anesthesia Gases dissolve in nerve tissue myelin (lipid layer) Altered electrical conduction of nerves Oxygen metabolized, does not build up Diminishes at-depth narcotic potency Lipids NOT total picture GABA receptors involved Complex Problem Not all understood LPT Nitrogen Narcosis Signs & Symptoms Warm, clear water: euphoria (“Laughing Gas” as model) Tendency to giggle Tunnel vision (syncope) Idea fixation (repetitive behaviors) Shortened attention span Declining neuro-muscular coordination Numb lips Inability to concentrate Cold, limited visibility water: dread Sense of being stalked (“It” is out there … somewhere) Loss of confidence (sense of helplessness) Intense anxiety LPT Nitrogen Narcosis Symptoms exacerbated by: cold work load (CO2) anxiety fatigue drugs alcohol menses (?) Symptoms: Typically noticeable ~ 100 fsw, but onset as shallow as ~ 60 fsw Sense of well-being: masks CNS impairment May be not be noticed by affected diver Individually variable CNS impairment increases with time / depth Ascent relieves problems; typically, no residuals LPT Underwater “Narcosis Test” “OK” signal is “automatic reflex” Narcosis Test Often NOT reliable indicator (for cognitive processing) Show 1 to 4 fingers to diver Diver adds 1 to # fingers Shows added count LPT Nitrogen Narcosis: Classic Myth Narcosis is reason for 130 fsw sport diving depth limit Turns out, 130 fsw is US Navy limit to use vintage scuba on a salvage dive ‘cause At the time diving rules were established, Double hose regulators would not support hard working below 130 fsw LPT Carbon Dioxide (CO2) Carbon Dioxide Metabolic waste product Potent vasodilator Helps maintains blood pH Breathing “Trigger” Excess levels in blood most undesirable CO2 produced faster than eliminated CO2 Production: Resting: 300 mL/min Working: 2000 mL/min (unfit person has >> production) LPT Carbon Dioxide (CO2): Major Problem in Diving Sources of Carbon Dioxide: Contaminated Gas (very rare) Work load exceeding ventilation “Skip Breathing” Poor ventilation (equipment dead space) snorkel poor regulator full face mask LPT Cardinal Rule of Diving “Never Hold You Breath” But, you hold your breath every time you breathe with a regulator Breathing On Surface: Inhale … exhale … hold Breathing With Regulator: Inhale … hold … slow exhale … hold During the hold, you are: holding breath (embolism risk) building up CO2 Don’t consciously extend the “hold phase” (called “skip breathing”) LPT Hypercapnia (High CO2) A CO2 “Hit” Slight CO2 build-up Increased respiration (attempt to vent) Poor ventilation CO2 continues to increase High CO2 perceived as “regulator not working” Suspicion: many “out of air” emergencies are CO2 hits LPT CO2 Cascade Carbon dioxide exacerbates most dive maladies Increased O2 in EANx raises density Greater density increases work of breathing Israeli military studies: Breathing EANx increases CO2 retention LPT Hypercapnia (High CO2) Studies show oxygen-enriched air promotes CO2 retention Higher the O2 concentration, the greater the effect Greater density at depth requires more work to breathe Important to monitor breathing Suspect CO2 build-up Stop Breathe slowly (Imagine STOP sign) Until breathing returns to normal LPT Hypercapnia (High CO2) Main Diving Issues: Respiratory Starvation Headache Center of forehead LPT Carbon Monoxide (CO) CO binds to hemoglobin 250x > O2 Too much CO No O2 lethal From incomplete