1. Volkmar Schröder BAM, D-12200 Berlin Folie 1 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Explosion Characteristics of Hydrogen-Air and Hydrogen-Oxygen Mixtures at elevated Pressures Volkmar Schröder and Kai Holtappels (BAM, Department II "Chemical Safety Engineering") 1Introduction 2Hydrogen explosion limits measured with different standard test methods 3Temperature influence on the explosion limits 4Pressure influence on the explosion limits of hydrogen-air mixtures 5Pressure influence on the explosion limits of hydrogen-oxygen mixtures 6Explosion pressure and rate of pressure rise 7Abstract and conclusions Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions

2. Volkmar Schröder BAM, D-12200 Berlin Folie 2 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 The main building of the Federal Institute of Materials Research and Testing (BAM) in Berlin Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions

3. Volkmar Schröder BAM, D-12200 Berlin Folie 3 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Outdoor test site in Horstwalde, south of Berlin Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions

4. Volkmar Schröder BAM, D-12200 Berlin Folie 4 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 The departments of BAM (Staff: About 1500 employees) Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions

5. Volkmar Schröder BAM, D-12200 Berlin Folie 5 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Motivation  Contamination of hydrogen is an essential problem for high pressure water electrolyzers.  The exact knowledge of explosion limits is necessary.  Databases contains explosion limits which are however mainly measured according to standard procedures at atmospheric conditions.  A new European standard for the determination of explosion limits (EN 1839:2003) have compared with older standards ASTM E 681-01 and DIN 51649.  Within the framework of the European research project SAFEKINEX and other projects explosion limits (EL), explosion pressures (pex) and rates of pressure rises ((dp/dt)ex) of hydrogen-air and hydrogen-oxygen mixtures were measured at elevated conditions.  The temperature and pressure dependence have been investigated. Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions

6. Volkmar Schröder BAM, D-12200 Berlin Folie 6 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions DIN 51649-1 - Open vessel - Glass cylinder (D=60 mm, L=300 mm) - Mixture preparation: Partial pressure and purging of the glass tube - Ignition source: High voltage spark - Criterion: Flame detachment (visually) ASTM E 681-01 - Open vessel - Glass flask, 5 dm 3 - Mixture preparation: Partial pressure - Ignition source: High voltage spark - Criterion: Flame detachment (visually)

7. Volkmar Schröder BAM, D-12200 Berlin Folie 7 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 EN 1839 (B), Bomb Method - Closed spherical vessel - Volume 14 dm 3 - Mixture preparation: partial pressure - Ignition source: fusing (exploding) wire - Criterion: pressure rise of  5% Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions EN 1839 (T), Tube Method - Open vessel - Glass cylinder (D=80 mm, L=300 mm) - Mixture preparation: Partial pressure and purging of the glass tube - Ignition source: High voltage spark - Criterion: Flame detachment (visually)

8. Volkmar Schröder BAM, D-12200 Berlin Folie 8 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions Explosion limits of hydrogen according to different standard test methods DIN 51649EN 1839 (T)EN 1839 (B)ASTM E 681 LEL (H 2 -Air)3.83.64.23.75 UEL (H 2 -Air)75.876.677.075.1 LEL (H 2 -40%N 2 -Air)3.6 4.43.65 UEL (H 2 -40%N 2 -Air)38.238.438.237.3  The standard test methods shows differences. The open vessel methods (ASTM, DIN, EN 1839 (B)) yield comparable LELs.  The closed vessel method (EN 1839 (B)) yields the highest lower explosion limit. The pressure threshold criterion seems to be less sensitive than the visual criterion.  Possibly upper explosion limits are influenced by the vessel sizes. EN 1839 (B) has the largest vessel size (14 dm 3 ).

9. Volkmar Schröder BAM, D-12200 Berlin Folie 9 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions Temperature influence on the explosion limits

10. Volkmar Schröder BAM, D-12200 Berlin Folie 10 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions Temperature influence on the explosion limits Table 2. Influence of the temperature on the explosion limits of hydrogen-air mixtures, measured at atmospheric pressure according to DIN 51649-1 Temperature in °C Lower explosion limit in mol% H 2 Upper explosion limit in mol% H 2 203.975.2 1003.477.6 2002.981.3 3002.183.9 4001.587.6 where LEL(T0) = 4.1 mol% and K L = 0.00157 K -1 where UEL(T0) = 74.5 mol% and KU = 0.00044 K -1

11. Volkmar Schröder BAM, D-12200 Berlin Folie 11 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions Influence of the initial pressure on the explosion limits of hydrogen-air mixtures, measured at room temperature

12. Volkmar Schröder BAM, D-12200 Berlin Folie 12 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions Influence of the initial pressure on the explosion limits of hydrogen-oxygen mixtures, measured at room temperature and 80 °C

13. Volkmar Schröder BAM, D-12200 Berlin Folie 13 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions Explosion pressure and rate of pressure rise p ex Explosion pressure, peak value of the time dependent pressure, measured in a closed vessel upon deflagration of an explosive gas mixture. p max Maximum explosion pressure, maximum value of the explosion pressure determined by varying the fuel concentration. F= p ex /p 0 Pressure rising factor, explosion pressure divided by the initial pressure. (dp/dt) ex Rate of pressure rise, highest value of the rate of pressure rise during a deflagration of a certain gas mixture. (dp/dt) max Maximum rate of pressure rise, maximum value of (dp/dt) ex determined by varying the fuel concentration. K G (dp/dt) ex related to a 1 m 3 vessel, characteristic value calculated according to the cubic law with the rate of pressure rise K G = (dp/dt) ex * V 1/3

14. Volkmar Schröder BAM, D-12200 Berlin Folie 14 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions Explosion pressures of hydrogen-air mixtures at 20 °C and different initial pressures

15. Volkmar Schröder BAM, D-12200 Berlin Folie 15 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions Rates of explosion pressure rises (K G values) of hydrogen-air mixtures at 20 °C and different initial pressures

16. Volkmar Schröder BAM, D-12200 Berlin Folie 16 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions Explosion pressures (pressure rising factors) of hydrogen-air mixtures at 10 bars and initial temperatures of up to 250 °C

17. Volkmar Schröder BAM, D-12200 Berlin Folie 17 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions Explosion pressures (pressure rising factors) of hydrogen-air and hydrogen- oxygen mixtures at 1 bar(a) and room temperature

18. Volkmar Schröder BAM, D-12200 Berlin Folie 18 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions Test No.amount of H 2 in mol% F (p ex /p 0 ) K G in bar m s -1 LEL = 4.6 mol% H 2 H000052a10.03.539.3 H900052a9.02.694.1 H800052a8.02.513.3 H700052a7.01.761.7 H600052a6.01.400.8 H550052a5.51.340.5 H500052a5.01.110.2 H480052a4.81.050.1 H460052a4.61.010.1 Explosion indices for H 2 /O 2 gas mixtures at 20 °C and at an initial pressure of 5 bar (6-dm 3 -vessel)

19. Volkmar Schröder BAM, D-12200 Berlin Folie 19 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions Abstract and conclusions  Explosion limits are not the type of independent physicochemical material characteristics. EL are influenced by the test apparatus. For proper use it is necessary to know their transferability to practical conditions (closed vessel, flame propagation through pipes etc.). Consequently the new European standard EN 1839 recommends two determination methods and the corresponding explosion limits have to be indicated clearly.  The explosion range of hydrogen becomes wider with increasing temperature. The quantitative influence can be described by a linear approximation.  Contrary to most of the other flammable gases the LEL of hydrogen increases with increasing initial pressure. The pressure dependence of the UEL shows a remarkable anomaly. After decreasing up to an initial pressure of about 20 bars, the UEL increases again.  Since hydrogen has a very high diffusion coefficient, especially hydrogen impurities in the oxygen gas are to be expected during the technical operation of electrolyzers. The pressure rising factors and K G values of such mixtures increase very slowly when the lower explosion limit is exceeded at only a few mol%. For these mixtures pressure resistant vessels and pressure relief devices (rupture disks, safety valves) can be used effectively.

20. Volkmar Schröder BAM, D-12200 Berlin Folie 20 International Conference on Hydrogen Safety, Pisa, September 8-10, 2005 Contents: Title 1. Introduction - Motivation 2. Standard Test Methods - Test Methods - Results 3. Temperature Influence 4. Pressure Influence - H2/air 5. Pressure Influence - H2/O2, 6. Explosion pressure, rate of pressure rise 7. Abstract and conclusions ACKNOWLEDGEMENTS The authors wish to thank for the financial support by the Research Center Jülich, Germany, and the European Commission within the Fifth Framework Programme on Energy, Environment and Sustainable Development, project SAFEKINEX.