Fire Hazards of Vehicles Powered by Alternative Fuels Including Hydrogen, CNG, and Electricity

1. DC Section of SAE October 23, 2008 Fire Hazards of Vehicles Powered by AlternativeFuels Including Hydrogen, CNG, and Electricity Peter B. Sunderland Assistant Professor, Dept. of Fire Protection Engineering University of Maryland, College Park

2. NIST grant under the technical management of J. Yang. FPRF grant under the technical management of K.A. Almand. R.L. Axelbaum (Washington Univ.), B.H. Chao (UHI), J.A. Milke (UMD) Students: M.S. Butler, K.M. Levy, C.W. Moran, N.R. Morton. Acknowledgments

3. Motivation • Gasoline presents many fire risks, but 100+ years of experience is helpful. • Diesel is the safest vehicle fuel in terms of fire. • U.S. vehicles have 266,000 fires annually, resulting in 350 deaths, 1230 injuries, and $1B damages (Ahrens, 2005). • Fires occur in only 2.6% of fatal crashes and in only 0.1% of all crashes (Plotkin, 2000). • In U.S. there are 30,000 fire departments and 1M firefighters, 75% of whom are volunteers.

4. EPAct • The Energy Policy Act (1992, 2005) seeks enhanced energy security and improved air quality. • EPAct defines alternative fuels as: • - Alcohols (e.g., methanol and ethanol) • - Natural gas • - Petroleum gas • - Coal-derived liquid fuels • - Hydrogen • - Electricity • - Biodiesel • - P-series • EPAct requires 75% of each federal fleet’s urban light duty vehicle acquisitions to be AFVs.

5. Vehicle Fire Statistics • USFA’s National Fire Incident Reporting System (NFIRS) • Fire cause and origin • Voluntary, but 42 states participate • DOT’s Fatal Accident Reporting System (FARS) • Fatal accidents only • Fire cause and origin not reported • Fuel type not reported • NFPA annual fire department survey • NFPA overviews (Ahrens, 2005)

6. Ethanol, Methanol, Biodiesel, Flex-fuel Hazards • Similar hardware as traditional fuel vehicles • Materials compatibility issues • Requires alcohol fire suppression precautions • Identification problems (can be both flex-fuel and hybrid) • Alcohols conduct electricity • Dim flames • Toxic runoff

7. Hybrids http://reviews.cnet.com Ford Escape Hybrid, 2005 7 of 35

8. Electric Vehicles Toyota RAV4 EV Emergency Response Guide, 1997

9. Hybrid and Electric Vehicle Hazards • Flammable fuels (hybrids) • Toxicity of plume and runoff • High voltage/current • Possible GFI failure • Extrication complications • Engine activation complications

10. CNG and Propane Toyota Camry CNG Emergency Response Guide, 1999 Orion VII CNG Bus Components

11. CNG and Propane Hazards • High pressure gas • Catastrophic tank failure • BLEVE (if liquefied) • Overhead fuel storage • Gas accumulation • Pressure relief device issues

13. CNG and Hydrogen vehicle containers require PRDs, primarily to protect against impinging fires. Modern composite tanks are good thermal insulators that weaken at high temperatures. Fuel pressure may not increase significantly during an impinging fire. A container may not be filled with fuel at the time of the fire. PRDs can be activated by pressure, temperature, or a combination. Most hydrogen, CNG, and propane containers are protected by temperature activated PRDs. PRD Activation

14. Mirada Bayonet PRD Rolander et al. (2003)

15. Summary of Vehicle PRD Codes

16. One container each at 98% and 24% of service pressure. Horizontal placement above a linear fire, such as a diesel pool, 1.65 m long. Average temperature 25 mm below the container of at least 430 C. PRD shielded with “a box made from thin steel plate.” To pass test, in 20 minutes containers must either vent down to 100 psig (6.9 bar) or not rupture. Many have recommended an improved bonfire test. FMVSS 304 Bonfire Test

17. Two CNG bus fires resulted in safe venting by the PRDs. A CNG Ford Crown Victoria in a fire experienced a container rupture in 2003. A CNG Honda Civic ruptured in 2007 (below). CNG Vehicle PRD Case Studies Seattle FD (2007).

18. Swain (2001) tests comparing hydrogen and gasoline vehicle fires (above). Hydrogen Vehicle PRD Test

19. Hydrogen Fuel Cell Toyota FCHV Emergency Response Guide, 2006

20. Hydrogen

21. Steel embrittlement. Lightest fuel, thus requiring the highest storage pressure. Highest volumetric leak propensity of any fuel. Permeation leaks. Smallest ignition energy of any fuel in air (28 J). Lowest autoignition temperature of any fuel ignited by a heated air jet (640 °C). Wide flammability limits in air (4 – 75% by volume). Highest laminar burning velocity of any fuel in air (2.91 m/s). Smallest quenching distance of any fuel premixed with air (0.51 mm). Highest heat of combustion (120 kJ/g). Dimmest flames of any fuel in air. Unique Fire Hazards of Hydrogen

22. A small leak develops in a H2 system, e.g., a H2 vehicle. The leak could arise from H2 embrittlement, H2 permeation, impact, equipment failure, or improper repair. The leak ignites from static discharge or heat. The leak burns undetected for a long period, damaging the containment system and providing an ignition source for a subsequent large release. Present Fire Scenario

23. Measure quenching and blowoff limits for H2, CH4 and C3H8 on small round burners. Measure quenching limits for leaky compression fittings. Examine material degradation arising from exposure to H2 and CH4 flames. Objectives

24. Quenching and blowoff limits Fuels: H2, CH4, and C3H8 Diameters: 8 m – 3.2 mm Leaky compression fittings Materials degradation Fuels: H2 and CH4 Materials: aluminum alloy 1100, galvanized steel, stainless steel, SiC Test times: up to 300 hours Experimental

25. Quenching Scaling Flame length: Lf / d = a Re = 4 mfuela / (  μ d ) Length at quenching: Lf = Lq / 2 Equating these: mfuel = π Lq μ / ( 8 a )

26. H2 Pinhole Quenching Limit • A H2 flame at its quenching limit is shown. • This flame is not visible to the eye and required 30 s camera exposures. • Stand-off height is about 0.25 mm. • Thermocouples were used to identify flaming conditions.

27. Quenching limits are nearly independent of d. H2 has the lowest quenching limit and the highest blowoff limit. CH4 and C3H8 have similar quenching and blowoff limits. Tube Burner Limits

28. Upstream pressure required for 5.6 g/s H2 isentropic choked flow is shown. For H2 at 690 bar, any hole larger than 0.4 m will support a stable flame.  Quenching Orifice Diameter

29. Weakest Flames • At left is H2 flowing downward into air (3.9 g/s, 0.46 W). • At right is H2 flowing downward into O2 (2.1 g/s, 0.25 W). • The tube inside and outside diameters are 0.15 and 0.30 mm. • The exposure time was 30 s. • The previous record was 0.5 –1 W, for H2 flame balls (Ronney et al. 1998).

30. Leak path for loose fittings. Leaky Fittings Tests • Flow rates were measured downstream of the leaks.

31. Quenching Limits 6.4 mm tube

32. Upstream Pressure Effects • Quenching limits for a 6 mm compression fitting are shown. • Limits are independent of pressure. • Limits are about 10X those of tube burners. • H2 limits are the lowest.

33. Materials Degradation

34. Al Degradation 10 mm Aluminum / H2 1 – hr exposure

35. Aluminum failed in H2 flame at 8 hours. Al Degradation

36. Corrosion after prolonged H2 flame exposure. 304 SS Degradation

37. SiC Degradation • SiC filaments failed at 12 minutes in the H2 flame, and at 356 minutes in the CH4 flame.

38. Control specimen Al Degradation Microscopy

39. Specimens following exposure to H2 flame Al Degradation Microscopy

40. Intumescent paints Steel wool or ceramic blankets Flame detectors: Cable heat detectors UV and IR detectors Possible Hydrogen Mitigation Strategies

41. Alternative fuels present unusual fire hazards. Hydrogen is probably the most unusual of all. These fuels may not be inherently more hazardous than gasoline and diesel, but further research is needed. Summary