1. Data for the evaluation of hydrogen RIsks onboard VEhicles : outcomes from the French project DRIVE ---- Gentilhomme O., Proust C., Jamois D., Tkatschenko I., Cariteau B., Studer E., Masset F., Joncquet G., Amielh M. et Anselmet F.
International Conference on Hydrogen Safety September 12-14, 2011

2. Sources of motivation
Hydrogen widely used in many industrial applications with good safety records
But current safety procedures and technologies will provide only limited guidance for transport industry:
H2 used in “decentralized” infrastructure (= car)
H2 used in relatively small amount (= several kg per user)
H2 used by a large population with no special training regarding the handling of such flammable gas
To gain full public acceptance, important to identify all risks and to succeed in controlling them

3. Sources of motivation
Hydrogen widely used in many industrial applications with good safety records
But current safety procedures and technologies will provide only limited guidance for transport industry:
H2 used in “decentralized” infrastructure (= car)
H2 used in relatively small amount (= several kg per user)
H2 used by a large population with no special training regarding the handling of such flammable gas
To gain full public acceptance, important to identify all risks and to succeed in controlling them
… but, despite all these vehicles, only limited data on safety aspects !!!

4. Overall presentation of DRIVE
DRIVE : Data for the evaluation of hydrogen RIsks onboard VEhicles
Duration :
Partners : CEA, IRPHE (CNRS centre), PSA Peugeot Citroën and INERIS
Total budget : 2000 kEuros (partly financed by the French national research agency)

5. Main objective of DRIVE
To produce experimental data on the whole reaction chain leading to a hydrogen hazard onboard vehicle,
Leakage
H2 build up and ATEX formation
Ignition
Hydrogen jet flame
Explosion

6. Leak quantification
“The range and frequencies of occurrence of leakage rates that will occur with hydrogen vehicles are unknown to us, despite our literature search” [BARLEY et al., ICHS in San Sebastian, 2007]
Observation confirmed by the initial work of DRIVE
Propose to classify the leakage in three types :
Probability
Gravity

7. Leak quantification
“The range and frequencies of occurrence of leakage rates that will occur with hydrogen vehicles are unknown to us, despite our literature search” [BARLEY et al., ICHS in San Sebastian, 2007]
Observation confirmed by the initial work of DRIVE
Propose to classify the leakage in three types :
Definitely an area where further data are required
Probability
Gravity

8. Leak quantification
Test rig to measure the leakage from key components of the H2 vehicle after they were submitted to various situations (ageing, bad fitting, damage…)
Rig capable to measure leakage as low as L/min H2

9. Leak quantification

10. Leak quantification
Most of the leakage arose due to insufficient tightness – pay attention to the maintenance !

11. ATEX formation
Hydrogen leakage taking place within a vehicle parked in a domestic garage or underground parking = one of the most dreadful scenario !
Important to understand all the mechanisms leading to the build-up of a potential ATEX
Yet most of the previous studies were focused on the gas distribution within the garage (BARLEY et al., 2007, VENETSANOS et al., 2010, ADAMS et al., 2011…) but rarely on the vehicle itself (MAEDA et al., 2007).

12. ATEX formation
Tests carried out within a private garage ( 5,8 × 3,0 × 2,4 m) with a real car parked inside
Leakage (diffuse source or jet) simulated with helium at various locations : under the bonnet, under the chassis and near the storage area
Leak flow rates varying between 0,05 and 600NL/min  it covers both the chronic and accidental leakages
Concentration monitored by means of catharometers

13. ATEX formation
Saturated concentration (% v/v) measured in the engine compartment vs the leakage flow rate (NL/min)

14. ATEX formation
X  Q2/3
Variation of the saturated concentration resulting from a diffuse leak follows the displacement regime identified by LINDEN [1999]
Saturated concentration (% v/v) measured in the engine compartment vs the leakage flow rate (NL/min)

15. ATEX formation
Insufficient tightness can lead to a concentration under the bonnet on the order of 10 % v/v (in the flammable range of H2)
Saturated concentration (% v/v) measured in the engine compartment vs the leakage flow rate (NL/min)

16. Explosion under the bonnet
Tests performed in two steps :
In a rig
In the real vehicle

17. Explosion in the rig
Example of results : homogenous concentration of 12,7 % v/v

18. Explosion in the rig
Example of results : homogenous concentration of 12,7 % v/v

19. Explosion in the rig
Example of results : homogenous concentration of 12,7 % v/v

20. Explosion in the rig
Example of results : homogenous concentration of 12,7 % v/v

21. Explosion in the rig
Example of results : homogenous concentration of 12,7 % v/v

22. Explosion in the rig
Example of results : homogenous concentration of 12,7 % v/v
Bear in mind the possible formation of a secondary explosion (outside the engine compartment)

23. Explosion under the bonnet
Comparison of the results between rig / real vehicle
P1 : pressure measured inside the engine compartment
P3 : pressure measured outside the engine compartment
Overpressures in the real vehicle slightly higher that those in the rig (filling ratio under the bonnet not exactly the same)
Pressure effects negligible when averaged H2 concentration < 10 % v/v.

24. Jet fires from the vehicle
Description of the testing facility

25. Jet fires from the vehicle
Visible flame length as a function of the release flow rate
Flame width  1/6 of its length
Measured temperature within the flame as high as 1500°C (a person fully or substantially engulfed by the flame will suffer fatality)
Lethal and irreversible effects due to thermal radiation will be limited to 1 – 2 m from the flame surface

26. Jet fires from the vehicle
Visible flame length as a function of the release flow rate
Flame width  1/6 of its length
Measured temperature within the flame as high as 1500°C (a person fully or substantially engulfed by the flame will suffer fatality)
Lethal and irreversible effects due to thermal radiation will be limited to 1 – 2 m from the flame surface
Safety distances on the order of 10 m all around the H2 vehicle !

27. Jet fires from the vehicle
How to reduce the safety distances associated with the PRD functioning ?
 By impacting the PRD release on the road ?
Taken from [HOUF et al, 2008]

28. Jet fires from the vehicle
How to reduce the safety distances associated with the PRD functioning ?
 By impacting the PRD release on the road ?
Probably not enough !
Taken from [HOUF et al, 2008]

29. Conclusions
DRIVE = one of the rare projects focused on the safety use of H2 onboard vehicle
3 types of leakages :
Permeation leakage : permanent but release flow rate so low that passive safety means should be sufficient (design of engine compartment, detection…)
Accidental leakage : massive leakage but very rare. Active safety means (calibrated orifice, excess flow valve…) will be required
Chronic leakage : arises due to the ageing of the vehicle or bad maintenance. More problematic since it features a high probability of occurrence and a release flow rate as high as NL/min
Pressure effects due to an explosion under the bonnet will not be significant if maximum H2 concentration limited to 10 % v/v. Concentration not exceeded if release flow rate less than 10 NL/min. But bear in mind the possible formation of secondary explosion !!!

30. Thanks for your attention !!!