1. Japan Automobile Research Institute
ID 146
The possibility of an accidental scenario for marine transportation of fuel cell vehicle -Hydrogen releases from TPRD by radiant heat from lower deck-
Yohsuke tamura
Japan Automobile Research Institute
Kenji Sato
Toho University
Thank you very much for the introduction.
My name is TAMURA, from Japan Automobile Research Institute.
I will present about　the possibility of an accidental scenario for marine transportation of fuel cell vehicle.

2. Situation of activated TPRD
Hydrogen gas
TPRD
Hydrogen　tank
Hydrogen　tank
Flame
Ignition
I would like to talk about an event by thermal pressure relief device activation.
The hydrogen gas CFRP tank is fitted with the TPRD.
TPRD’s are the safety devices intended to avoid rupture of the tank by releasing the filling gas in the event of a fire.
The hydrogen releases are immediately burned by the flames existing around TPRD.
The hydrogen releases are immediately burned by the flames existing around TPRD.

3. Marine transportation for FCV
Next, Let’s think about marine transportation for FCV.
A pure car carrier or a ferry boat have some deck of steel structure.
A pure car carrier or a ferry boat having decks of steel structure.

4. An accident scenario of fire from lower deck
HFCV
Hydrogen cylinder
Deck floor heated by the fire
TPRD
Lower deck
Upper deck
This figure shows that an accident scenario of fire from lower deck.
In this scenario, a fire accident breaks out in a lower deck,
and heats up the FCVs parked on the upper deck.
The tanks installed on the underbody portion of the HFCV.

5. An accident scenario of fire from lower deck
Fire by parts of the vehicle
Deck floor heated by the fire
If the parts of vehicle were ignited by radiant heat in case of a fire accident on the lower deck before TPRD activation,

6. An accident scenario of fire from lower deck
Hydrogen flame
The hydrogen releases are immediately burned by the flames existing around TPRD.
Therefore, it will be no explosion.
No explosion!

7. An accident scenario of fire from lower deck
HFCV
Hydrogen cylinder
TPRD
Lower deck
Upper deck
Deck floor heated by the fire
However, if TPRD is activated by the radiant heat without the presence of flames in upper deck,
Assuming that TPRD is activated by the radiant heat without the presence of flames in upper deck, hydrogen gas will be released by TPRD to form combustible air-fuel mixtures which may cause explosion.

8. An accident scenario of fire from lower deck
TPRD from hydrogen gas
When hydrogen gas is released by TPRD, combustible air-hydrogen mixtures may cause explosion.
Assuming that TPRD is activated by the radiant heat without the presence of flames in upper deck, hydrogen gas will be released by TPRD to form combustible air-fuel mixtures which may cause explosion.

9. Contents To investigate the possibility of this accident scenario,
An experimental study of the relationship between radiant heat and TPRD activation time.
When the temperature of the deck is self-ignition temperature of the plastic parts of the vehicle, radiant heat flux q of TPRD is calculated. Then q and qc are compared.
In the absence of flame, it was examined whether or TPRD is activated by radiant heat from the floor.
o investigate the potential of this accident scenario,
we have conducted as the following.
One is an experimental study of the relationship between radiant heat and TPRD activation time.
Second,
When the temperature of the deck is self-ignition temperature of the plastic parts of the vehicle,
Radiant heat flus q of TPRD is calculated.
Then q and qc are compared.
Finally, In the absence of flame, it was examined whether or TPRD is activated by radiant heat from the floor.

10. Performance test for TPRD by radiant heat
Thermocouple
Fuse metal type #B #C
TPRD　name
Normal working pressure [MPa]
Type
Nominal activated temperature #A
35MPa
Fuse metal
104oC #B
110oC #C
70MPa #D
Glass bulb
Glass bulb type #D
Thermocouple
Now, I will talk about performance test for TPRD radiant heat.
This study was designed to experimentally determine relations between radiant heat and TPRD activation time.
All the four sample TPRDs are types used in automotive compressed hydrogen tanks.
Types A, B and C each incorporate in its stainless steel body a fuse metal that melts at its nominal activating temperature.
Type D incorporates a glass bulb which contains a fluid and is ruptured at its nominal activating temperature by the thermal expansion of the fluid.
A large portion of the glass bulb is embedded in TPRD’s stainless steel body to protect from external impacts.
Activated temperature of TPRD are about 110 degree.  
This mark shows point of the surface temperature of the TPRD metal body.
This was measured by a K-type thermocouple.
Glass bulb

11. Test method To predict TPRD’s activation time under radiant heat
This figure show that diagrams of the test method.
The TPRD was pressurized by helium gas to more than 2 MPa.
Radiant heat was applied to the TPRD from a cone-shaped heater.
The TPRD set on the fiberglass to insulate from the installation stand.
Four intensities of radiant heat was applied: 15, 30, 50 and 75 kW/m2.
The maximum heating duration was set at 1 hour.
The time required from heat application to TPRD activation was measured.

12. TPRD Body Temperature when TPRD activated
I will talk about result of performance test of TPRD.
This figure shows that TPRD stainless body surface temperature when TPRD activated.
Bule is 30KW/m2, Yellow is 50KW/m2, Red is 70Kw/m2.
Fuse metal type TPRD's that is A,B,C body temperature is higher than TPRD's activation temperature.
However, Glass bulb type D body temperature is lower than TPRD activation temperature.
Fuse metal type TPRD’s (A,B,C) body temp. > TPRD’s activation temp.
Glass bulb type TPRD(D) body temp < TPRD activation temp.

13. TPRD Body Temperature when TPRD activated
TPRD A,B,C (Fuse metal type)
The heat must be transmitted from the body surface to the embedded fuse metal through the TPRD body having a certain heat capacity.
TPRD D (Glass bulb type)
The radiant heat reached the glass bulb directly from an aperture in the TPRD body.
Glass bulb type #D
That reason is as follow.
In the case of TPRD A,B,C, the heat must be transmitted from the body surface to the embedded fuse metal through the TPRD body having a certain heat capacity.
however, in the case of TPRD D, The radiant heat reached the glass bulb directly from an aperture in the TPRD body.

14. Relationship with TPRD activation time ＆ radiant flux
Next, I will explain that that relationship with TPRD activation time and radiant flux.
Vertical axis is TPRD activation time tac.
Horizontal axis is radiant flux qac.
Lines of the TPRD A,B,C are almost on the same line.

15. Relationships with 1/TPRD activation time ＆ radiant flux
Critical radiant flux qc
This figure shows the relationship between radiant flux and the reciprocal of activation time.
This line is the average activation time of the three fuse metal type TPRDs A,B,C.
As you can see, there was a linear relationship between the reciprocal of activation time and radiant flux.
Furthermore, the performances of the three fuse metal type TPRDs were plotted virtually on the same straight line.
The intersection point of this line and the horizontal axis indicated the maximum radiant heat at which TPRD remained inactive.
This point is called the critical radiation qc.

16. Relationships with TPRD activation time ＆ radiant flux
Regression formulae
Critical radiant flux qc
[kW/m2] #A
(Fuse metal)
4.77 #B
5.17 #C
4.88 #D
(Glass bulb)
24.8
This table shows the regression formula, critical radiant flux qc.
The value of critical radiant flux proved to be approximately 5 kW/m2 for the fuse metal type TPRDs, and approximately 25 kW/m2 for the glass bulb type TPRD.
The lower of the two critical radiant flux values was employed in the rest of the present study in view of greater safety for FCV marine transportation.

17. Discussion - Radiant Heat Model
 Radiation shape factor
Next, Let’s calculate radiant heat flux q of TPRD ,when the temperature of the deck is self ignition temperature of the pｌastic parts of vehicle.
First, the amount of heat flux received by TPRD from lower deck when the tire reached its spontaneous ignition temperature was calculated by the radiant heat model.
The TPRD was assumed to receive only the radiant heat from lower deck as its heat input.
The lower-deck dimensions were set at 105m x 68m on the basis of the actual floor sizes of pure car carrier ships.
The TPRD position was set at 0.09m from floor.
Although the actual TPRDs installed on FCVs are guarded with an undercover for protection against aerodynamic force and splash stones from the ground.
Therefore this case assumed the worst case of a missing undercover.
As the result, radiation shape factor is 1.

18. Discussion - Fire by tire
Heat flux q received by TPRD when the floor temp. was 400°C, the self-ignition temperature of tire rubber.
The emissivity ɛ ＝ 0.16~0.35 (TPRD’s body:stainless steel)
Stefan-Boltzmann constant σ =5.67  10-11[kW/m2K-4]
The critical radiant flux necessary for TPRD activation is 5 kW/m2.
TPRDs would not activate under the floor temperature condition equal to the self-ignition temperature of tire.
Cabin would be burnt down due to ignition of tire before TPRD activation.
Heat flux q received by TPRD when the floor temperature was 400°C, the self-ignition temperature of tire rubber.
As the TPRD body is made mostly of stainless steel, the emissivity ɛ of TPRD is 0.16~0.35, whereby 0.35 was selected for calculations.
The amount of heat flux received by TPRD is 4.07 kw/m2, when the floor temperature was 400°C, the spontaneous ignite on temperature of tire rubber.
The critical radiant flux necessary for TPRD activation is 5 kW/m2.
TPRDs would not activate under the floor temperature condition equal to the self-ignition temperature of tire.
Therefore, Cabin would be burnt down due to ignition of tire before TPRD activation.

19. Discussion - Fire by undercover
FCVs have a plastic undercover.
Undercover : Polypropylene ⇒ Softening temperature °C
Self-ignition temperature 498 °C
On the other hand, most of the commercialized FCVs have their hydrogen cylinders guarded by a plastic undercover for protection.
Accordingly the radiant flux from the lower deck would first heat the undercover before heating the TPRD.
With these plastic undercovers made primarily of polypropylene, their softening temperature is known to be 128°C and spontaneous ignition temperature 498°C.
When subjected to radiant heat from lower deck, therefore, the polypropylene undercover first softens and drops onto the floor before TPRD activation.
When subjected to radiant heat from lower deck, the polypropylene undercover first softens and drops onto the floor before TPRD activation.

20. Discussion - Fire by undercover
Deck floor temp. 500°C (the self-ignition temperature of PP)
Calculated by radiation model
The radiant heat q　received by TPRD ：7 kW/m2
Relationships with TPRD activation time ＆ radiant flux
Then, given a deck floor temperature of 500°C ,approximately the self-ignition temperature of polypropylene.
the radiant heat qac received by TPRD was calculated to be about 7 W/m2.
From the relationships with TPRD activation time and radiant flux, TPRD activation needs to be exposed to radiant heat for 90minutes.
Therefore the Polypropylene undercover fallen onto the floor would have undergone self-ignition before TPRD activation.
TPRD activation needs to be exposed to radiant heat for 90 min..
The PP undercover fallen onto the floor would have undergone self-ignition before TPRD activation.

21. Conclusions
This study was conducted to examine the accident scenario for FCV marine transportation during which fires may break out in the lower deck and induce TPRD activation in the FCVs parked on the upper deck.
The experiment on relationships between TPRD activation time and radiant heat from the lower deck found that it took at least 90 minutes for TPRD to activate under the condition of lower-deck temperature reaching the spontaneous ignition temperature of FCV tires and polypropylene parts; that even if polypropylene parts are melted and self-ignited under radiant heat, hydrogen releases would be burned immediately by the flames present in the vicinity. Accordingly it was concluded that the explosion of air-fuel mixtures assumed in the accident scenario cannot occur in the real world.
This study was conducted to examine the accident scenario for FCV marine transportation during which fires may break out in the lower deck and induce TPRD activation in the FCVs parked on the upper deck.
The experiment on relationships between TPRD activation time and radiant heat from the lower deck found that it took at least 90 minutes for TPRD to activate under the condition of lower-deck temperature reaching the spontaneous ignition temperature of FCV tires and polypropylene parts; that even if polypropylene parts are melted and self-ignited under radiant heat, hydrogen releases would be burned immediately by the flames present in the vicinity. Accordingly it was concluded that the explosion of air-fuel mixtures assumed in the accident scenario cannot occur in the real world.

22. Thank you for your attention.
ご清聴頂きまして有難うございました．
This paper introduces one of the achievements of the “technology development project for hydrogen production, transport and storage systems” commissioned by New Energy and Industrial Technology Development Organization (NEDO) in Japan.