INFLUENCE OF HYPERBARIC BREATHING GASES ON DEEP DIVERS

Transcription

1 Technical Sciences 113 INFLUENCE OF HYPERBARIC BREATHING GASES ON DEEP DIVERS Tamara STANCIU * tamarastanciu@navyro Cecilia ADUMITRESI ** cadumitresi@yahoocom * Diving Center, Constanţa, Romania ** Ovidius University, Constanţa, Romania ABSTRACT The ability of a diver to ass the dee diving course is tested through trials that evaluate the tolerance of a diver to hyerbaric resiratory gases Three of these tests take lace in the hyerbaric chamber in order to highlight the effect of oxygen and inert gases over the diver, during ressurization These are: the Oxygen test, the Narcosis test and HPNS (High Pressure Nervous Syndrome) If the first two tests are frequently executed, HPNS was resumed and imroved at Hyerbaric Comlex of Diving Center Hyothermia is another stress factor in the hyerbaric environment that has been studied and was identified by a series of dives at different deths of immersion in wet simulator of Diving Center The exerimental results were consistent with calculated temerature losses reviously established by mathematical model KEYWORDS: Oxygen, Nitrogen, Helium, HPNS (High Pressure Nervous Sy ndrome), Hy oth ermia 1 Introduction Diving activity below 60 m, resumes the use of the synthetic breathing mixtures The most imortant gas for the life is oxygen Very active, it is easily combined with other inert gases, used as diluents These are: nitrogen, helium or argon Every gas from the breathing mixture is influenced by its artial ressure : g rg am (1) where r g is the volumetric articiation of gas from the mixture; is the ressure of breathing mixture am g The influence of these gases at high ressures is different from individual to individual, therefore the Normative about organization and labour s rotection in diving activity imosed secific tests for each from mixture s comonents [1] 2 The Comonent Gas Effects of Breathing Mixtures under Pressure 21 Hyerbaric Oxygen The limits required by oxygen in diving, were exerimentally determined and are resented in a diagram (Figure no 1) [2] On the x axis there can be seen the the diving deth and the ressure, on the y REVISTA ACADEMIEI FORŢELOR TERESTRE NR 1 (77)/2015

2 114 Technical Sciences axis there can be seen the oxygen concentration (% O 2 ) and the inert gas concentration (% inert gas) into mixture Curve I reresents the lower limit curve of the security zone, with the artial ressure of oxygen ox 017 bar; above of this curve, is the hyoxia and anoxia area Curve II reresents the higher limit curve of the security zone, over this curve exists the hyeroxia zone, with the artial ressure of oxygen ox 2 bar The dashed curve is the normoxia curve, corresonding to a artial ressure of oxygen ox 0 21bar, which is the artial ressure of oxygen for the normobaric air Fig no 1 Security Limits Imosed by Oxygen Partial Pressure The exosure time (latency time) of human body to hyoxia and hyeroxia is very imortant The reaction time during the hyeroxia, varies from individual to individual or it differs even in the same individual, deending on the effort, temerature, fatigue Oxygen toxicity dose can be quantified as a Unit Pulmonary Toxicity Dose (UPDT), which is determined by Lemaire formula: 2 UPDT ( ox) t (2) where t(hours) is the exosure time to hyerbaric oxygen ox is the ressure of oxygen In conclusion, longer time divin g lanning must take into account two asects: The oxygen artial ressure to the storage deth (saturation secific term: the stationary rofounder into dry hyerbaric chamber) must be stationary to 03 04bar; The oxygen artial ressure must be greater than 05 bar, to decomression, but must not exceed the Unit Pulmonary Toxicity Dose The oxygen test for divers is resented in the Normative about organization and labour s rotection in diving activity [1, ca 45] The divers are ressured into the dry hyerbaric chamber to 18m ( ox 2 8bar ) and insire ure oxygen from the mask during 25 minutes If the ulse is over 100, the diver doesn t ass the test 22 Hyerbaric Nitrogen The atmosheric air contains 21 % oxygen and 79 % nitrogen, which is the natural diluent of oxygen The nitrogen high artial ressure induces a narcotic effect to the diver Excet for helium and REVISTA ACADEMIEI FORŢELOR TERESTRE NR 1 (77)/2015

3 Technical Sciences 115 robably neon, all gases that can be breathed have a narcotic effect Nitrogen narcosis is a reversible alteration in consciousness that occurs while diving at deth it may decrease the effectiveness of the diver until death The two hases are excitation and inhibition Nitrogen narcosis aears to low artial ressure, n bar (deth greater than 40m for normobaric air)for other diluent gases, narcosis aears at larger deths An imortant disturbance factor is the diver s sensibility to nitrogen, disturbance which is tested according to the Normative about organization and labor s rotection in diving activity The narcosis test consists in a memory and a mathematical test, which are effectuated first to surface and than after a raid ressuring (6 minutes) to 72m dee [1, ca 46] If the errors made under ressure are 30 % greater than to the surface, the candidate is inat for dive deeer than 40m 23 Hyerbaric Helium Diving activity below 40-60m, when the atmosheric air induces nitrogen narcosis, resumes the use of the another inert gases for the breathing mixtures, excet the nitrogen The most roerly is helium The mixture of helium with oxygen forms a synthetic breathing gas, Heliox, which has an indistinguishable narcotic effect At diving below 150m, at high comressing seed, there have been noted symtoms of disturbances of the central nervous system (dizziness, nausea, vomiting, ostural tremor, fatigue and somnolence, decrements in intellectual and sychomotor erformance, increasing and decreasing of wave activity of the brain, as measured by an electroencehalogram) These symtoms are known as HPNS (High Pressure Nervous Syndrome) These symtoms start at different deth ressures for various subjects, deending on the hysical resistance It was necessary to establish scales of fitness, to erform a dee diving course After Fructus [3], the symtoms are divided in two categories: Clinical symtoms: tremor, dissymmetry, muscle convulsions, somnolence EEG symtoms: EEG modifications, increase of Theta waves activity, deression of Alha and Beta waves activity, sleeing erturbations In general, tremor aears at diving bellow 150 m, at high comressing seed and it is characteristic at the extremities (fingers) and increases with deth The tremor observed in dee diving with Heliox, was named helium tremor, but it also aeared during dee dives with hydrogen Peter Bennet describes in his book behavioral disorders that occur in raid ressurization at 183 m and have decreased the math skils tests at the 18 % and 25 % dexterity [4] The study of this henomenon has been made by Diving Center too, on hyerbaric comlex, serviced by its team of qualified technicians The test was made in a dry chamber, with two teams of 3 divers (without the tender diver), during the dee diving course [5, 6] The hydrostatic ressure and Heliox effects on the divers were verified by HPNS (High Pressure Nervous Syndrome) testing, in accordance with the rules from Normative about organization and labour s rotection in diving activity [1, ca 47] Before comressing, the followin g information was recorded from the divers: electroencehalograhy, in suine osition, without luminous stimulus; ostural tremor Realization of Electroencehalograhy rocedure The equiment used for recording is a technology of a medical nature, rovided by Naval Medicine Center (EEG aaratus) REVISTA ACADEMIEI FORŢELOR TERESTRE NR 1 (77)/2015

4 116 Technical Sciences and the neurologist made the electroencehalogram for first team, at surface, in the following conditions: oen eyes; close eyes; at hyerventilation; after hyerventilation; in suine osition; without luminous stimulus The silver electrodes were fixed on the scal and it was recorded the electrical otential of the sontaneous activity of the cortical neurons The electric signals were transmitted to the central rocessor which rocessed them with the rogrammer Neuron Sectrum Realization of ostural tremor rocedure After EEG test, the three subjects were tested at ostural tremor For ostural tremor, the recordings were made using electronic equiment by registration of the subject s fingers oscillations and by transmission of electric signals to comuter Equiment is made from accelerometer sensor (Figure no 2), fixed on the median finger of the diver, which transmits the electric oscillations of a comuter The oscillations are recorded and then measure the frequency and amlitude The MMA7361L accelerometer is an electro mechanic transducer of vibration measurement low ower, small size Fig no 2 Conection Diagram of the MMA7361L Accelerometer The transducer for ostural tremor was fixed on the median finger of the right hand, tensed on horizontal and were recorded the signals into a comuter, during 20 seconds, 20 seconds ause and 20 seconds with the hand susended near the body For each subject two such recordings were made After finish of the surface recorders, the subjects were comressed at deth 180 m, with v 10m / min, in the dry chamber of the Hyerbaric Laboratory, with Heliox 95/5 over the existing atmosheric gas To avoid the hyeroxia henomenon due to the existing air at atmosheric ressure (nitrogen oxygen 79/21), into dry hyerbaric chamber, the evolution of the artial ressures was determined, deending on entire breathing gas ressure (Figure no 3) REVISTA ACADEMIEI FORŢELOR TERESTRE NR 1 (77)/2015

5 Technical Sciences 117 Fig no 3 Partial Pressures Evolution of the Gases from the Hyerbaric Chamber, during the Pressuring between m, with Heliox (95/5) over the Atmosheric Pressure (Nitrogen-oxygen 79/21) The oxygen s artial ressure finally reaches 1100 mbar absolute, where the divers can t be exosed over 3 hours according to NOOA (National Oceanic and Atmosheric Administration) and actually, less 3 hours after U S Navy The Nitrogen artial ressure remains constant Ni = 790 mbar After 10 minutes ause, the tests were resumed at 180 m deth, in the same conditions (Figure no 4, Figure no 5) Fig no 4 EEG Registrations under Pressure (180 m) into the Hyerbaric Chamber Fig no 5 Postural Tremor Registrations under Pressure (180 m) into the Hyerbaric Chamber REVISTA ACADEMIEI FORŢELOR TERESTRE NR 1 (77)/2015

6 118 Technical Sciences In order to establish the diving roficiency scale at EEG the following is considered for each subject: Alha waves average amlitude from 180 m deth, comarative with the surface value slow Delta waves average amlitude from 180 m deth, comarative with the surface value Dominant frequency of the tremor was 8-10 Hz After comression, there weren t found modifications of the tremor frequency After the registration, the ostural tremor s amlitude was quantitatively calculated in millimeters and qualitatively in ercent, deending on the value obtained at atmosheric ressure Considering the results of measurements obtained now and in the ast years and the reaction of the tested divers, it settles the roficiency scale for dee divers: 1) The increase of 1-10 Hz EEG waves over 35 %; 2) The increase of ostural tremor s amlitude over 150 %; 3) The increase of mathematic calculus errors over 50 % These reresent unsuitability criteria at dee diving (bellow 150 m), at large comressing seeds ( v 8m / min ) 3 Thermal Effects of Hyerbaric Breathing Gases By solving the differential equation that governs the transfer of heat in wet hyerbaric simulator (the two ways of heat loss are through conduction and convection-skin and resiratory systemheating and humidification of the gaseous mixture), we get the solution of the body temerature T [K] [7]: T T 1 ( ) c V ( ) R Qm l x V ( ) ( ) ( ) ( ) mc Q m l b T ( ) 0 W e 1 1 ( ) cv R R( ) x( ) V cv T W (3) where c breathing mixtures secific heat, at constant ressure [ J / kgk ], m - body mass [kg] ; c b body core secific heat, c b 3470[ J / kgk ]; m 2 heat flux, [ W / m ] ; c Q Q metabolic heat flux lost at 2 skin level, [ W / m ] ; r heat flux lost at 2 resiratory system level, [ W / m ] ; T-body temerature, [K]; t-time, [s], l latent secific heat of vaorization [ J / kg ], Q breathing mixtures density, 3 kg / m ; x () absolute humidity of breathing mixture [ kg / kg] ; V resiratory volume flow rate, 3 [ m / s] The equation was verified in a series of dives at different deths of immersion, conducted in the wet simulator of the Diving Center in Constanţa: Air unit dives at 61 m and 31 m deth of immersion; Saturation dives with Heliox 95/5 at 61 m and 31 m storage deths Most hysical sizes involved, deend on the ressure and the characteristics of gases from the breathing mixture The total heat losses of a diver were about 2-3 times higher than when using Heliox as breathing gas than in air, for subjects with the same hysical characteristics (Figure no 6) It was found abrut loss of body heat divers to greater deths, and in articular to saturation Helium causes roblems because the coefficient of thermal REVISTA ACADEMIEI FORŢELOR TERESTRE NR 1 (77)/2015

7 Technical Sciences 119 conductivity k 352[ cal cmsk ] and secific heat at constant volume c v 0745[cal/g K] are high comared to nitrogen that are used in air, resectively k 58[ cal cmsk ] and c v 0177[cal/g K], this values lead to a dangerous cooling of the divers Fig no 6 Heat Flow Resiratory Gas Humidification Lost, Two Divers with Similar Physical Characteristics, Breathing Air and Heliox 95/5, at the Same Deth Hyothermia is deendent on: deth: the mathematical relationshi of heat loss is observed ressure deendence of several factors (deth); k thermal conductivity coefficient of diluents gas; c v mass secific heat at constant volume, of diluents gas Dee diving, which breathing is a synthetic mixture, Heliox 5/95 in this case, are influenced by all three factors listed above Comfort temerature hyerbaric environment must be maintained at a higher level than the atmosheric ressure to avoid hyothermia 4 Conclusions When working underwater, at a nigger deth, it is recommended the usage of Heliox, saturation or unit diving The exosure time during a saturation dive is high enough that all body tissues to be saturated with inert gas from the breathing mixture; inert gas is absorbed into the blood and the body tissues, with over 120 minutes semi saturation eriod, during long-term exosure The ressure of the dissolved gas in the tissue is equal to that of the gas in the lungs and the diver can stay in this stage for a long eriod of time, without any neurological and sychomotor roblems (HPNS) After the saturation oint has been reached during the decomression, the additional exosure will not increase Dee diving oerations are thus more effective In order to avoid the thermal stress induced by abrut cooling of breathing mixtures, using helium as the diluents gas, it is recommended to estimate the temerature of thermal comfort (equation 3) into diving chamber To maintain this temerature, during simulated dives, it is recommended to use heated sealed suits, during the real diving, into the natural environment REVISTA ACADEMIEI FORŢELOR TERESTRE NR 1 (77)/2015

8 120 Technical Sciences Testing dee divers, accordin g Normative about organization and labor s rotection in diving activity is treated very seriously by SCAFS (Deartment of Research and Training Advisory Divers) of the Center, to maintain security secialist staff REFERENCES 1 Normative about Organization and Labour s Protection in Diving Activity, (Military Navy, 1996) 2 Mircea Degeratu, Aron Petru, Ştefan Georgescu and Sergiu Ioniţă, Hyerbaric Technologies for Bounce and Saturation Dive, Ca V: Exosure to Pressure and Decomressing of Divers, (Bucharest: MATRIX ROM, 2008) 3 X Fructus and RL, Sciarli, Security and Health of Diving (La longée santé et securité), (Paris: Editions Maritimes et d Outre-Mer, 1980) 4 Bennett and Elliott s, Physiology and medicine of diving, 5th Edition, (Edinburgh: Saunders, 2003), Mihai Diaconu, Tamara Stanciu and Mircea Degeratu, Monitorization and Evaluation of HPNS, Annals of Management and Technological Engineering, (Oradea, June 2013) 6 Mihai Diaconu, Tamara Stanciu and Mircea Degeratu, The Procedure by Evaluation of Divers for the Dee Diving, (Bucharest: Academia Oamenilor de Ştiinţă din România Sesiunea Ştiinţifică de Primăvară, Secţiunea de Ştiinţe Tehnice, May 9, 2014) 7 Anca Constantin and Tamara Stanciu, Transient Heat Transfer in Subsea Hyerbaric Environment, 13 th International Multidiscilinary Scientific GeoConference SGEM, Marine and Ocean Ecosystems, (Albena, Bulgaria, June 16-22, 2013): 871 REVISTA ACADEMIEI FORŢELOR TERESTRE NR 1 (77)/2015