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Mathematical Modeling of the Processes Occurring in Gas Mixtures Used in Hyperbaric Facilities
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 85 (2016) 2 – 8
Sustainable Solutions for Energy and Environment, EENVIRO - YRC 2015, 18-20 November 2015, Bucharest, Romania
Mathematical modeling of the processes occurring in gas mixtures used in hyperbaric facilities Elena Felicia Alboiua, Mircea Degeratua, Nicolae Ioan Alboiua* a
Technical University of Civil Engineering, Lacul Tei Bvd., no. 122 – 124, RO 020396, sector 2, Bucharest
Abstract Diving is one of the domains in which humans are facing a totally different environment from that in which they live normally. Depending on the purpose of the underwater mission and the diving depth to be reached, some special installations and breathable gas mixtures are used to sustain life in such an environment. Diving chambers are hyperbaric facilities used for forming, training, testing and in unfortunate circumstances rescuing divers. The paper deals with the mathematical modeling of the phenomenon taking place in a hyperbaric facility during the compression and decompression phases of a saturation diving. For this purpose the authors of the present paper have conceived a mathematical model with which, the values of the main quantities forming a breathable gas mixtures delivered to the divers are established for each diving depth during the entire mission. ©2015 The Authors. Published by Elsevier Ltd. © 2016 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee EENVIRO 2015. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee EENVIRO 2015 Keywords: Hyperbaric processes; diving chamber; saturation diving, breathable gas mixtures
1. Background and aims One of the domains using hyperbaric facilities is the diving area. The hyperbaric processes are those developed at pressure values higher as the normal one (atmospheric pressure). Regardless if professional divers are operating in scientific, industrial or military field they are periodically trained and tested in high pressure conditions. For accomplishing safely any mission, the deep diving procedures impose the necessity of using hyperbaric equipment like the diving (hyperbaric) chambers (figure 1).
* Corresponding author. Tel.: +4-021-243-3660; fax: +4-021-243-3660. E-mail address: [email protected]
1876-6102 © 2016 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee EENVIRO 2015 doi:10.1016/j.egypro.2015.12.268
Elena Felicia Alboiu et al. / Energy Procedia 85 (2016) 2 – 8
For professional diving missions air, which is used mostly for recreational scuba diving, is replaced with other breathing mixtures made from two (binary mixtures) or three (ternary mixtures) gases. One of the gases is oxygen and the others are inert gases. The role of the inert gases in the mixture is to counteract the neurotoxic effect of oxygen breathed at high pressure values.
Fig. 1. The diving chamber and the associated control panel owned by the Dive Center of Constanța
The major problems using gas mixtures for deep diving are related to the purity of the compound, the ratios between the components, the effect of oxygen breathed at high pressures and as a consequence, the decompression procedure. Thus, breathing mixtures are made in diverse ratios of the constituent gases. Their amount is in close relationship with the diving depth and thus, with the partial pressure of the gases. The common inert gases used for deep diving are nitrogen and helium. Their role is to dilute oxygen and together to form a binary breathing mixture called NITROX (NITRogen - OXigen) respectively HELIOX (HELIum OXigen) or all three together a ternary mixture named TRIMIX. The amount of each gas that from the mixture is close related to the characteristic quantities of each of the gases and the diving depth.
a)
b)
Fig. 2 Hyperbaric laboratory equipment. (a) pressurization/decompression command panel of a diving chamber system; (b) air treatment plant.
A major role in operating any hyperbaric facility plays the diving technology which is linked to the mission particularities. Manufacturing of breathing mixtures is a very complex process which must be done very carefully and following a series of precise rules. The processes related to the compression and decompression phases for a unitary saturation diving are achieved by a rigorous monitoring of the procedures concerning the breathing gas mixtures composition present in the hyperbaric chamber and the compression and decompression phases at different moments. The authors of the present paper have conceived a mathematical model in order to simulate the compression and decompression procedures of any saturation diving mission. Thus, based on this mathematical model the phenomena taking place in a hyperbaric facility (diving chamber) during a deep diving mission can be theoretically simulated.
3
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Elena Felicia Alboiu et al. / Energy Procedia 85 (2016) 2 – 8
2. Proposed mathematical model used for saturation diving simulation The mathematical model conceived by the authors of the paper can be used for any kind of gaseous breathing mixture preparation and regardless of the diving depth. However to demonstrate the effectiveness of the model the present paper deals only with HELIOX breathing mixtures used for a deep diving mission. To determine the values of the characteristic quantities the established mathematical relationships have considered the succession of the processes occurring in the diving chamber during the compression and decompression phases and the specific equations related to gas mixtures. To determine the mass of the HELIOX mixture, which is pressure dependent, relationship 1 is used. M mix
V p air RHeOx p HeOx Rair T Rair RHeOx
(1)
The total mass of oxygen is composed from the oxygen present initially (at normal pressure) in the diving chamber and the oxygen of the HELIOX mixture used for the compression process. The mass of oxygen is the product of the density, pressure and volume. The total mass of oxygen is: t M Ox
U Ox p1VOx U Ox pVOx
(2)
But VOx is the product of the oxygen present in the air and also in the HELIOX mixture and the total mixture volume: VOx
rOxV
(3)
Thus relationship (2) can be written in a final shape as: t M Ox
U OxV ( p1rOx1 prOx2 )
(4)
which is used to compute the mass participation of oxygen. From all tree gases the mass of nitrogen (Ni) present in the air is the only one which remains constant.
M Ni
U Ni rNiVp
(5)
In relationship (5) U is the density of the gas; rNi the volume participation; V is the volume and p the pressure. The mass of helium ( He ) present in the HELIOX mixture is computed in the same way using the following relationship:
M He
U HerHeVp
(6)
3. Mathematical simulation of a diving mission using the proposed computing method and the obtained results To establish the effectiveness of the mathematical model conceived by the authors of the present paper, a 180 m saturation diving mission was considered, and one of the obtained results were compared with those of a similar real diving. The analyzed scenario assumes initially that the hyperbaric chamber is filled with air (79%Ni and 21%Ox) at normal pressure. Then the pressurization process with HELIOX mixture 95/5 (95% He and 5% Ox) is made up to 180 m (19 bar – absolute scale). During the process the partial pressure, mass participations and volume
5
Elena Felicia Alboiu et al. / Energy Procedia 85 (2016) 2 – 8
participation variations of the gases were considered. Thus, the general relationships used to compute the physical quantities of interest were established. Using the relationships presented in chapter 2, the masses of each component of the air (Ox and Ni) and also of the mixture (He and Ox) were computed. The general valid relationship used for the mixture mass computing is (1) written in this case as: M mix
air V Rair p RHeOx pOx RHeOx T Rair
(7)
As shown in relationship (7) the gas constants of air and HELIOX mixture and also the pressure of each component and the volume and the temperature of the mixture were considered. The characteristic constants were previous computed for different pressure values according to the diving depth. In order to compute nitrogen and helium relationship (5) and (6) were used. When computing the total masses of oxygen both oxygen quantities present in the air and in the HELIOX mixture should be summed. This must be done taking into account that the oxygen mass in the air remains constant unlike the oxygen mass from the HELIOX mixture that is depth (pressure) dependent. M Ox
air U Ox rOxaer V pOx U Ox rOxHeOx V p
(8)
To compute the volume participation of each constituent (Ox, Ni, He), general valid relationships (9), (10) and (11) were obtained.
air ROx V Rair p RHeOx pOx p RHeOx Rair
rOx
mOx
rHe
mHe
rNi
mNi
(9)
air RHe V Rair p RHeOx pOx p RHeOx Rair
air RNi V Rair p RHeOx p Ni p RHeOx Rair
(10)
(11)
Depending on the total pressure of the mixture and also on the mass of oxygen from both air and HELIOX the following relationship used for computing the partial pressure of oxygen was established: pOx = (5,5171 + 1,3136·10-5·p)·3806,2165
(12)
In a same way the relationships used for computing of the nitrogen (Ni) and helium (He) partial pressures were obtained: pNi = 1,1494·10-5·p·15,8·(4350,0245:p)
(13)
pHe = 0,1642·10-5·19·p·30450,025
(14)
Some of the computed results for the compression phase of the considered diving mission are plotted in figure 3 and figure 4.
6
Elena Felicia Alboiu et al. / Energy Procedia 85 (2016) 2 – 8
PARTIAL PRESSURE VARIATION - HELIOX 5/95 mixture over air -
Partial pressure p [bar]
18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Oxygen Helium Nitrogen
0
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 Depth H [m]
Fig. 3. The correlation of the partial pressure of the gases of interest with the diving depth VOLUME PARTICIPATION VARIATION - HELIOX 5/95 mixture over air 1 0.9
Volume participation [-]
0.8 0.7 0.6 Oxygen 0.5
Nitrogen
0.4
Helium
0.3 0.2 0.1 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 Depth [m]
Fig. 3. The correlation of the volume participation of the gases of interest with the diving depth
Applying the proposed mathematical model for a diving chamber from which the air was extracted first, the obtained results during the decompression process for the main characteristic quantities of the gases which form the breathing mixture HELIOX were compared with those measured in a hyperbaric facility during the decompression phase of a similar saturation diving mission. One of the theoretically results obtained by applying the described mathematical model versus the measured values of the quantities of interest are presented graphically in figure 5 and figure 6.
Elena Felicia Alboiu et al. / Energy Procedia 85 (2016) 2 – 8
PARTIAL PRESSURE VARIATION - Decompression process20 18
Partial pressure [bar]
16 14
Ox (computed)
12
He (computed)
10
He (measured)
8 Ox (measured)
6 4 2 0 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10
0
Depth [m]
Fig. 5. Comparison between the mathematical model results and the measured values during the decompression phase of the real diving mission. Partial pressure variation
VOLUME PARTICIPATION VARIATION - Decompression process 1.00 0.90 Ox (computed)
Volume participation [-]
0.80 0.70
He (computed)
0.60 0.50
He (measured)
0.40 Ox (measured)
0.30 0.20 0.10 0.00 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 Depth [m]
0
Fig. 6. Comparison between the mathematical model results and the measured values during the decompression phase of the real diving mission. Volume participation variation
Analysing the two graphs plotted in figure 5 and figure 6, the similarity of the data obtained by applying the proposed mathematical model and those measured in the hyperbaric facility is obvious. 4. Concluding remarks By comparing the two data sets namely the computed one, obtained by using the mathematical model, and the measured data, the effectiveness of the proposed computing procedure is demonstrated. Essentially the mathematical model can be applied for diverse breathing mixtures preparation and any saturation diving mission. Applying the presented mathematical model during the preparation phase of any saturation diving mission will be an effective predictive tool for the diving team which will provide, beside the experience gained over years, more confidence regarding their decisions related to the adopted diving schedule. In the future the proposed mathematical model can serve for the automation of hyperbaric installations.
7
8
Elena Felicia Alboiu et al. / Energy Procedia 85 (2016) 2 – 8
References [1] Bruce R., Wienke and Timothy R., O’Leary, Mixed Gas Decompression Theory with Algorithms and Statistics RGBM Technical Series 6 NAUI Technical Diving Operations Tampa, Florida 33619. [2] Degeratu M., Petru A., Georgescu Şt. Aparate de respirat sub apa, Editura MatrixRomBucuresti 2010. [3] Degeratu, M., Petru, A., Ioniţă.,S. Manualul scafandrului. Ed. Per Omnes Artes, Bucureşti, 1999. [4] Petru A. Hidraulica proceselor hiperbare Teză de doctorat Universitatea tehnică de construcţii Bucureşti 1993. [5] Stanciu T., Diaconu M., Degeratu M. Monitorization and Evaluation of HPNS (High Pressure Nervous Syndrome) ANNALS OF THE ORADEA UNIVERSITY Fascicle of Management and Technological Engineering ISSUE #1, pg. 375 JULY 2013. [6] Şandru E., Bianchi A.M., Mihăilă C., Caluianu V., Antonescu N. Termotehnică şi aparate termice; Editura Didactică şi Pedagogică, Bucureşti 1982. [7] The National Oceanic and Atmospheric Administration (NOAA), NOAA Diving Manual U.S. Department of Commerce and Best Publishing Company 2011. [8] *** U.S. Navy Diving Manual; SUPERSEDES SS521-AG-PRO-010, REVISION 5, August 2005 [9] http://www-personal.umich.edu/~lpt/mixhistory.htm - Diving With Gas Mixes Other Than Air by Larry "Harris" Taylor, Ph:D. [10] http://www.seasubsea.com/airquality/Air Quality Requirement for Nitrox Blending.
ScienceDirect Energy Procedia 85 (2016) 2 – 8
Sustainable Solutions for Energy and Environment, EENVIRO - YRC 2015, 18-20 November 2015, Bucharest, Romania
Mathematical modeling of the processes occurring in gas mixtures used in hyperbaric facilities Elena Felicia Alboiua, Mircea Degeratua, Nicolae Ioan Alboiua* a
Technical University of Civil Engineering, Lacul Tei Bvd., no. 122 – 124, RO 020396, sector 2, Bucharest
Abstract Diving is one of the domains in which humans are facing a totally different environment from that in which they live normally. Depending on the purpose of the underwater mission and the diving depth to be reached, some special installations and breathable gas mixtures are used to sustain life in such an environment. Diving chambers are hyperbaric facilities used for forming, training, testing and in unfortunate circumstances rescuing divers. The paper deals with the mathematical modeling of the phenomenon taking place in a hyperbaric facility during the compression and decompression phases of a saturation diving. For this purpose the authors of the present paper have conceived a mathematical model with which, the values of the main quantities forming a breathable gas mixtures delivered to the divers are established for each diving depth during the entire mission. ©2015 The Authors. Published by Elsevier Ltd. © 2016 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee EENVIRO 2015. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee EENVIRO 2015 Keywords: Hyperbaric processes; diving chamber; saturation diving, breathable gas mixtures
1. Background and aims One of the domains using hyperbaric facilities is the diving area. The hyperbaric processes are those developed at pressure values higher as the normal one (atmospheric pressure). Regardless if professional divers are operating in scientific, industrial or military field they are periodically trained and tested in high pressure conditions. For accomplishing safely any mission, the deep diving procedures impose the necessity of using hyperbaric equipment like the diving (hyperbaric) chambers (figure 1).
* Corresponding author. Tel.: +4-021-243-3660; fax: +4-021-243-3660. E-mail address: [email protected]
1876-6102 © 2016 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee EENVIRO 2015 doi:10.1016/j.egypro.2015.12.268
Elena Felicia Alboiu et al. / Energy Procedia 85 (2016) 2 – 8
For professional diving missions air, which is used mostly for recreational scuba diving, is replaced with other breathing mixtures made from two (binary mixtures) or three (ternary mixtures) gases. One of the gases is oxygen and the others are inert gases. The role of the inert gases in the mixture is to counteract the neurotoxic effect of oxygen breathed at high pressure values.
Fig. 1. The diving chamber and the associated control panel owned by the Dive Center of Constanța
The major problems using gas mixtures for deep diving are related to the purity of the compound, the ratios between the components, the effect of oxygen breathed at high pressures and as a consequence, the decompression procedure. Thus, breathing mixtures are made in diverse ratios of the constituent gases. Their amount is in close relationship with the diving depth and thus, with the partial pressure of the gases. The common inert gases used for deep diving are nitrogen and helium. Their role is to dilute oxygen and together to form a binary breathing mixture called NITROX (NITRogen - OXigen) respectively HELIOX (HELIum OXigen) or all three together a ternary mixture named TRIMIX. The amount of each gas that from the mixture is close related to the characteristic quantities of each of the gases and the diving depth.
a)
b)
Fig. 2 Hyperbaric laboratory equipment. (a) pressurization/decompression command panel of a diving chamber system; (b) air treatment plant.
A major role in operating any hyperbaric facility plays the diving technology which is linked to the mission particularities. Manufacturing of breathing mixtures is a very complex process which must be done very carefully and following a series of precise rules. The processes related to the compression and decompression phases for a unitary saturation diving are achieved by a rigorous monitoring of the procedures concerning the breathing gas mixtures composition present in the hyperbaric chamber and the compression and decompression phases at different moments. The authors of the present paper have conceived a mathematical model in order to simulate the compression and decompression procedures of any saturation diving mission. Thus, based on this mathematical model the phenomena taking place in a hyperbaric facility (diving chamber) during a deep diving mission can be theoretically simulated.
3
4
Elena Felicia Alboiu et al. / Energy Procedia 85 (2016) 2 – 8
2. Proposed mathematical model used for saturation diving simulation The mathematical model conceived by the authors of the paper can be used for any kind of gaseous breathing mixture preparation and regardless of the diving depth. However to demonstrate the effectiveness of the model the present paper deals only with HELIOX breathing mixtures used for a deep diving mission. To determine the values of the characteristic quantities the established mathematical relationships have considered the succession of the processes occurring in the diving chamber during the compression and decompression phases and the specific equations related to gas mixtures. To determine the mass of the HELIOX mixture, which is pressure dependent, relationship 1 is used. M mix
V p air RHeOx p HeOx Rair T Rair RHeOx
(1)
The total mass of oxygen is composed from the oxygen present initially (at normal pressure) in the diving chamber and the oxygen of the HELIOX mixture used for the compression process. The mass of oxygen is the product of the density, pressure and volume. The total mass of oxygen is: t M Ox
U Ox p1VOx U Ox pVOx
(2)
But VOx is the product of the oxygen present in the air and also in the HELIOX mixture and the total mixture volume: VOx
rOxV
(3)
Thus relationship (2) can be written in a final shape as: t M Ox
U OxV ( p1rOx1 prOx2 )
(4)
which is used to compute the mass participation of oxygen. From all tree gases the mass of nitrogen (Ni) present in the air is the only one which remains constant.
M Ni
U Ni rNiVp
(5)
In relationship (5) U is the density of the gas; rNi the volume participation; V is the volume and p the pressure. The mass of helium ( He ) present in the HELIOX mixture is computed in the same way using the following relationship:
M He
U HerHeVp
(6)
3. Mathematical simulation of a diving mission using the proposed computing method and the obtained results To establish the effectiveness of the mathematical model conceived by the authors of the present paper, a 180 m saturation diving mission was considered, and one of the obtained results were compared with those of a similar real diving. The analyzed scenario assumes initially that the hyperbaric chamber is filled with air (79%Ni and 21%Ox) at normal pressure. Then the pressurization process with HELIOX mixture 95/5 (95% He and 5% Ox) is made up to 180 m (19 bar – absolute scale). During the process the partial pressure, mass participations and volume
5
Elena Felicia Alboiu et al. / Energy Procedia 85 (2016) 2 – 8
participation variations of the gases were considered. Thus, the general relationships used to compute the physical quantities of interest were established. Using the relationships presented in chapter 2, the masses of each component of the air (Ox and Ni) and also of the mixture (He and Ox) were computed. The general valid relationship used for the mixture mass computing is (1) written in this case as: M mix
air V Rair p RHeOx pOx RHeOx T Rair
(7)
As shown in relationship (7) the gas constants of air and HELIOX mixture and also the pressure of each component and the volume and the temperature of the mixture were considered. The characteristic constants were previous computed for different pressure values according to the diving depth. In order to compute nitrogen and helium relationship (5) and (6) were used. When computing the total masses of oxygen both oxygen quantities present in the air and in the HELIOX mixture should be summed. This must be done taking into account that the oxygen mass in the air remains constant unlike the oxygen mass from the HELIOX mixture that is depth (pressure) dependent. M Ox
air U Ox rOxaer V pOx U Ox rOxHeOx V p
(8)
To compute the volume participation of each constituent (Ox, Ni, He), general valid relationships (9), (10) and (11) were obtained.
air ROx V Rair p RHeOx pOx p RHeOx Rair
rOx
mOx
rHe
mHe
rNi
mNi
(9)
air RHe V Rair p RHeOx pOx p RHeOx Rair
air RNi V Rair p RHeOx p Ni p RHeOx Rair
(10)
(11)
Depending on the total pressure of the mixture and also on the mass of oxygen from both air and HELIOX the following relationship used for computing the partial pressure of oxygen was established: pOx = (5,5171 + 1,3136·10-5·p)·3806,2165
(12)
In a same way the relationships used for computing of the nitrogen (Ni) and helium (He) partial pressures were obtained: pNi = 1,1494·10-5·p·15,8·(4350,0245:p)
(13)
pHe = 0,1642·10-5·19·p·30450,025
(14)
Some of the computed results for the compression phase of the considered diving mission are plotted in figure 3 and figure 4.
6
Elena Felicia Alboiu et al. / Energy Procedia 85 (2016) 2 – 8
PARTIAL PRESSURE VARIATION - HELIOX 5/95 mixture over air -
Partial pressure p [bar]
18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Oxygen Helium Nitrogen
0
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 Depth H [m]
Fig. 3. The correlation of the partial pressure of the gases of interest with the diving depth VOLUME PARTICIPATION VARIATION - HELIOX 5/95 mixture over air 1 0.9
Volume participation [-]
0.8 0.7 0.6 Oxygen 0.5
Nitrogen
0.4
Helium
0.3 0.2 0.1 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 Depth [m]
Fig. 3. The correlation of the volume participation of the gases of interest with the diving depth
Applying the proposed mathematical model for a diving chamber from which the air was extracted first, the obtained results during the decompression process for the main characteristic quantities of the gases which form the breathing mixture HELIOX were compared with those measured in a hyperbaric facility during the decompression phase of a similar saturation diving mission. One of the theoretically results obtained by applying the described mathematical model versus the measured values of the quantities of interest are presented graphically in figure 5 and figure 6.
Elena Felicia Alboiu et al. / Energy Procedia 85 (2016) 2 – 8
PARTIAL PRESSURE VARIATION - Decompression process20 18
Partial pressure [bar]
16 14
Ox (computed)
12
He (computed)
10
He (measured)
8 Ox (measured)
6 4 2 0 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10
0
Depth [m]
Fig. 5. Comparison between the mathematical model results and the measured values during the decompression phase of the real diving mission. Partial pressure variation
VOLUME PARTICIPATION VARIATION - Decompression process 1.00 0.90 Ox (computed)
Volume participation [-]
0.80 0.70
He (computed)
0.60 0.50
He (measured)
0.40 Ox (measured)
0.30 0.20 0.10 0.00 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 Depth [m]
0
Fig. 6. Comparison between the mathematical model results and the measured values during the decompression phase of the real diving mission. Volume participation variation
Analysing the two graphs plotted in figure 5 and figure 6, the similarity of the data obtained by applying the proposed mathematical model and those measured in the hyperbaric facility is obvious. 4. Concluding remarks By comparing the two data sets namely the computed one, obtained by using the mathematical model, and the measured data, the effectiveness of the proposed computing procedure is demonstrated. Essentially the mathematical model can be applied for diverse breathing mixtures preparation and any saturation diving mission. Applying the presented mathematical model during the preparation phase of any saturation diving mission will be an effective predictive tool for the diving team which will provide, beside the experience gained over years, more confidence regarding their decisions related to the adopted diving schedule. In the future the proposed mathematical model can serve for the automation of hyperbaric installations.
7
8
Elena Felicia Alboiu et al. / Energy Procedia 85 (2016) 2 – 8
References [1] Bruce R., Wienke and Timothy R., O’Leary, Mixed Gas Decompression Theory with Algorithms and Statistics RGBM Technical Series 6 NAUI Technical Diving Operations Tampa, Florida 33619. [2] Degeratu M., Petru A., Georgescu Şt. Aparate de respirat sub apa, Editura MatrixRomBucuresti 2010. [3] Degeratu, M., Petru, A., Ioniţă.,S. Manualul scafandrului. Ed. Per Omnes Artes, Bucureşti, 1999. [4] Petru A. Hidraulica proceselor hiperbare Teză de doctorat Universitatea tehnică de construcţii Bucureşti 1993. [5] Stanciu T., Diaconu M., Degeratu M. Monitorization and Evaluation of HPNS (High Pressure Nervous Syndrome) ANNALS OF THE ORADEA UNIVERSITY Fascicle of Management and Technological Engineering ISSUE #1, pg. 375 JULY 2013. [6] Şandru E., Bianchi A.M., Mihăilă C., Caluianu V., Antonescu N. Termotehnică şi aparate termice; Editura Didactică şi Pedagogică, Bucureşti 1982. [7] The National Oceanic and Atmospheric Administration (NOAA), NOAA Diving Manual U.S. Department of Commerce and Best Publishing Company 2011. [8] *** U.S. Navy Diving Manual; SUPERSEDES SS521-AG-PRO-010, REVISION 5, August 2005 [9] http://www-personal.umich.edu/~lpt/mixhistory.htm - Diving With Gas Mixes Other Than Air by Larry "Harris" Taylor, Ph:D. [10] http://www.seasubsea.com/airquality/Air Quality Requirement for Nitrox Blending.