1. 11th International Symposium on Fire Safety Science
February 9 – 14, University of Canterbury, Christchurch, New Zealand
Fire behaviors of Protective Coatings used for Hydrogen Composite Cylinders
D.-Q. DAO1,2, T. ROGAUME2, J. LUCHE2, F. RICHARD2, L.-B. VALENCIA3, S. RUBAN3
1Duy Tan University, Danang, Vietnam
2Département Fluides, Thermiques, Combustion, Institut Pprime, France
3Air Liquide, Centre de Recherche Claude-Delorme, France
Good morning everybody,
I am very glad to present to you the results of our experimental study concerning the fire safety for hydrogen composite cylinders.
In this presentation, I will concentrate on the protective performance of an intumescent paint and an ablative elastomer used as fire protective coatings.
Institut P’ • UPR CNRS 3346
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F86962 FUTUROSCOPE CHASSENEUIL Cedex
titre présentation
04/05/2018

2. Epoxy resin/carbon fiber composite cylinder
Context
The high-pressure (70 MPa/10.1 kpsi) fully wrapped epoxy resin/carbon fiber composite cylinder is currently the preferred option for fuel cell electric vehicle
Epoxy resin/carbon fiber composite cylinder
Light weight
Excellent mechanical performance
High capacity of H2 storage
Good chemical and electrical resistance
Cost
Gravimetric capacity
Volumetric capacity
H2 vehicle refilling station
Coming back to hydrogen application, the high pressure composite /'kɔmpəzit/ cylinder is currently considered as the preferred option for fuel cell electric vehicle. And it is also studied for on-site large capacity storages.
Their characteristics are light weight, excellent mechanical performance, high capacity H2 storage and good chemical and electrical resistance.
H2 fuel bus
D. Quang Dao et al. IAFSS 11th International Symposium, Paper 149, Feb 9 – 14, 2014
04/05/2018

3. Context TYPE IV cylinders
Epoxy resin/carbon fiber composite wall (few cm)
Polar boss (interface seal)
High molecular weight polymer liner (few mm)
TYPE IV cylinders
Foam dome (impact protection)
Protection layer (damage resistance)
Fire safety strategy: preventing the cylinder from bursting
However, the composite cylinders constitute /'kɔnstitju:t/ of the highly flammable /'flæməbl/ materials like fiber reinforced /,ri:in'fɔ:s/ composite, and polymer /'pɔlimə(r)/ liner.
When exposed to accidental fires, these materials may induce a high failure risk of cylinders like bursting.
So the generally accepted safety strategy consists in adding a release device and sometimes even a fire protective coatings.
Releasing hydrogen through a thermal pressure relief device and/or using a Fire protective Coating
D. Quang Dao et al. IAFSS 11th International Symposium, Paper 149, Feb 9 – 14, 2014
04/05/2018

4. Objective
To optimize the design of the fire protection of the cylinder
by improving the understanding of the thermal behavior of the epoxy resin/carbon fiber composites
by using the fire protective coatings
To examine the influence of a fire protective coating :
An intumescent paint,
An ablative elastomer,
on the Reaction-to-fire properties (time-to-ignition, mass loss, thermal response parameter, specific mass loss rate, temperature at coating/composite interface) of Carbon Fiber reinforced Epoxy resin composite.
This study is a part of longer and broader /broutʃ/ research program studying the fire behaviours of different materials such as composite laminate, thermoplastic liners and fire protective coatings used in high pressure hydrogen composite cylinders.
And ones of the main objectives are :
+ To optimize the design of the fire protection of the cylinders by a better understanding the thermal behaviors of epoxy resin /'rezin/ - carbon fiber composite, and by using fire protective coatings.
+ To examine the influence of a fire protective coating by an intumescent paint and an ablative elastomer.
D. Quang Dao et al. IAFSS 11th International Symposium, Paper 149, Feb 9 – 14, 2014
04/05/2018

5. Carbon fiber/Epoxy resin composite
Elementary analysis
Element
Pure epoxy resin
Composite 59 vol% CF C
70.6 %
84.6 % O
17.1 %
5.4 % H
8.5 %
2.9 % N
3.2 %
Residue
< 0.1 %
<0.1% Cl
0.1 %
390 ppm S
< 10 ppm
<10 ppm
Water -
0.3 %
Total
< 99.6 %
< 98.7 %
The epoxy resin/carbon fiber composites are pre-impregnated bands of commercial references
Thermal properties
The commercial epoxy /i'pɒksi/ composites used in this study are in pre-preg form, it means that the carbon fibre was pre-impregnated in the epoxy resin. This consists in the unidirectional ply /plai/ laminated composite.
The results of elementary analysis of pure epoxy resin and composite reinforced with 59 vol% CF are presented on the 1st table. We can see that the epoxy resin and the composite contained essentially four major elements C, O, H and N. And the presence of N-element is related to use of a reversible /ri'və:səbl/ amine /'æmain/ hardener /'hɑ:dnə/.
The second table displays the thermal properties of the epoxy/carbon composite such as: density, heat capacity, thermal diffusivity and thermal conductivity.
D. Quang Dao et al. IAFSS 11th International Symposium, Paper 149, Feb 9 – 14, 2014
04/05/2018

6. Fire protective coatings
1.0 mm – thickness – intumescent paint coating
(Anticorrosion protection alkyd-paint/
Solvent-phase intumescent paint/
Solvent-phase satin paint)
7.6 mm – thickness – ablative elastomer coating
(Elements: C, O, H, Si, B, Na, Ca, Fe, Pt
Adhesive: 0.5 mm-thickness elastomer)
Sample dimension
Length: 100 ± 0.5 mm, Width : 100 ± 0.5 mm
Sample mass
Two commercial coatings were used: an intumescent [,intju:'mesnt] paint and an ablative elastomer.
+The intumescent coating was respectively implemented by three different layers: an anticorrosion protection alkyd-paint serving as an adhesion /əd'hi:ʒn/ layer, a solvent-phase intumescent paint providing the thermal stability performance, and a solvent-phase satin paint for finishing the intumescent system.
+The ablative ['æblətiv] elastomer [i'læstəmə(r)] contained the chemical elements: C, O, H, Si, B, Na, Ca, Fe and Pt. The bonding of the ablator layer on the composite surface was performed by a 0.5 mm – thickness elastomer adhesive /əd'hi:siv/. The thickness ['θiknis] of the intumescent paint and ablative elastomer are respectively of 1 and 7.6 mm.
Finally, in order to measure the temperature at protective coating and composite layers, an thermocouple of 1mm-diameter was used. It was located at the sample centre, and mounted from the bottom to the top surface.
Samples
Initial mass
Composite
148.7±1.8 g
Intumescent layer
5.2±0.2 g
Ablative material
36.6±0.2 g
Thermocouple setup for temperature measurements
D. Quang Dao et al. IAFSS 11th International Symposium, Paper 149, Feb 9 – 14, 2014
04/05/2018

7. Cone Calorimeter experiments
Configurations:
Heat fluxes up to 75 kW.m-2
Piloted ignition
Air atmosphere
ISO 5660 test procedure
Measurements & calculus :
Mass loss
Mass loss rate (MLR)
Piloted ignition time (tig)
Temperature at coating/composite interface
Combustion gaseous species
The thermal decomposition tests were investigated in the ISO 5660 standard Cone Calorimeter under open air atmosphere ['ætməsfiə] and well-ventilated conditions. The cone heater can provide heat fluxes up to 75 kW/m2.
Several parameters characterizing the thermal degradation of the materials such as mass loss, mass loss rate, piloted ignition time, temperature at coating/composite interface and the burnt gases species were systematically measured and calculated.
D. Quang Dao et al. IAFSS 11th International Symposium, Paper 149, Feb 9 – 14, 2014
04/05/2018

8. Virgin composite – Decomposition phases
(1) Resin thermal cracking
(3) Combustion of the monomer solvent + Degradation of remained epoxy resin
As a result, the thermal decomposition and combustion of epoxy resin/carbon fibre takes place in four phases:
the thermal cracking of epoxy resin to form the low molecular weight gaseous species that leads to the flaming ignition, and char forming,
the acceleration of epoxy resin degradation jointly with the formation of monomer solvent. That is displayed by the first peak in the figure,
the combustion of the monomer solvent and degradation of remained epoxy resin that is represented by the second higher peak,
the oxidation of carbon ['kɑ:bən] char and carbon fibre decomposition.
40 kW/m2
(2) Acceleration of Resin decomposition + monomer solvent production
(4) Char oxidation + Carbon fiber decomposition
Decomposition phases
D. Quang Dao et al. IAFSS 11th International Symposium, Paper 149, Feb 9 – 14, 2014
04/05/2018

9. Virgin composite – Specific Mass Loss Rate
Specific Mass Loss Rate (g/m2.s)
20 kW/m2
CHF=14 kW/m2
The figure ['figə] above presents ['preznt] the evolutions of specific mass loss rate of the pure composite exposed to different external heat fluxes up to 75 kW/m2.
The critical heat flux for this material is about 14 kW/m2. And we can see that at the heat fluxes lower than 20 kW/m2, the thermal decomposition occurs in only one phase because of the first char layer forming from the cracking of epoxy resin. Upon that, the thermal decomposition takes place in two distinguished phases as discussed before.
And it can be seen that the more heat flux is important, the more rapidly the thermal decomposition occurs.
Time (s)
Heat flux   SMLR peak amplitudes   SMLR widths 
D. Quang Dao et al. IAFSS 11th International Symposium, Paper 149, Feb 9 – 14, 2014
04/05/2018

10. Virgin composite – Other thermal properties
Characteristic parameters of the composite thermal degradation
Thermal parameters
This work
Epoxy resin (1,2)
Epoxy resin / glass fiber (1)
Piloted ignition temperature Tig, K
575
650 – 800 -
Critical heat flux CHF, kW/m2 14
13 – 20
10 – 15
Thermal response parameter TRP, kW s0.5/m2
370
457
388 – 540
Thermal inertia P, kW2 s/m4 K2
2.25
0.38
Heat of gasification L, kJ/g 16
2.4
The table above resumes [ri'zju:m] the characteristic parameters of the thermal degradation of 59 vol% carbon fiber composite. The results obtained are also compared to the ones in literature.
In general, it’s found that the presence of carbon fibre causes a worse thermal resistance of material in fire with lower ignition temperature, lower critical heat flux, and thermal response parameter, but a higher value of thermal inertia and gasification heat.
Refs:
(1) Tewarson, A., The SFPE Handbook of Fire Protection Engineering (4th ed.), National Fire Protection Association, 2008, p. 3 – 109.
(2) Scudamore, M.J., Briggs, P.J., Prager, F.H., Fire and Materials, 1991, 15: 65 – 84.
D. Quang Dao et al. IAFSS 11th International Symposium, Paper 149, Feb 9 – 14, 2014
04/05/2018

11. Coating/Composite samples – Mass Loss Intumescent paint/composite
Ablator/composite
Mass loss (wt%)
Mass loss (wt%)
The two figures displays the evolution of mass loss level (wt%) of the coating/composite samples at different heat fluxes from 30 to 75 kW/m2. Below 30 kW/m2, no flaming ignition of the protected composite was detected, although the thermal decomposition of the protective coatings.
Generally, three decomposition phases can be observed. The first step consists in the thermal decomposition of protective coatings with a mass loss of about 2% and 6%. After this step, a thermal shield of char layer was formed at the exposed surface of composite layer.
The second step is related to the thermal decomposition of principal composite under the protection of the char layer. By comparing to the decomposition of the virgin composite, we see that the presence of a coating layer increases the decomposition time as well as reduces the mass loss levels.
And the last step consists in the oxidation of epoxy resin residue /'rezidju:/.
Time (s)
Time (s)
+ Below 30 kW/m2  No flaming ignition is detected
+ Adding a coating layer  Degradation time   Mass loss 
D. Quang Dao et al. IAFSS 11th International Symposium, Paper 149, Feb 9 – 14, 2014
04/05/2018

12. Coating/Composite samples – Ignition time
Ablator/Comp.
Piloted Ignition Time (s)
Intumescent/Comp.
Virgin Composite
The piloted ignition time of the composite at four irradiant levels from 30 to 75 kW/m2 under the thermal protection of the 2 coatings is displayed in this figure.
We can see that the two coatings used are all effective [i'fektiv] with a sharply increasing of piloted ignition time. The presence of insulating layers ensures /in'ʃuə/ that the protected composite is not ignited in the first 400 seconds.
And in general, the ablative elastomer presents a higher fire protective performance than the one of the intumescent paint.
Incident Heat Flux (kW/m2)
Adding a coating layer  Ignition time 
 Ablative elastomer >> Intumescent paint
D. Quang Dao et al. IAFSS 11th International Symposium, Paper 149, Feb 9 – 14, 2014
04/05/2018

13. Coating/Composite samples – Specific Mass Loss Rate
Virgin composite
40 kW/m2
30 kW/m2
SMLR (g/m2.s)
SMLR (g/m2.s)
These figures show the evolutions of specific mass loss rate of virgin composite and the 2 coating/composite systems exposed to different incident heat fluxes from 30 to 75 kW/m2.
The first peak represents the rapid thermal decomposition of the coatings. The second one consists in the thermal degradation of the protected composite that are significantly shifted to the right hand side of the picture.
These results show that the adding of the coating layer delays dramatically the thermal decomposition of composite. And once again, the ablator shows a better protective performance than the intumescent paint, especially in the high irradiant levels.
Intumescent/Composite
Ablator/Comp.
60 kW/m2
75 kW/m2
SMLR (g/m2.s)
SMLR (g/m2.s)
04/05/2018

14. Coating/Composite samples – Interface temperature
Using a protective coating  Temperature at interface 
At first 1200 s: Ablator >> Intumescent paint Both coatings are well adhered to the composite
After 1200 s: Ablator << Intumescent paint Ablator  broken / flaked Intumescent  adhered
Comp.
Intumescent
Temperature (K)
40 kW/m2
In order to evaluate the fire protective performance of each coating along the test, the temperature at the interface of coating layer and composite one was measured at different external irradiant levels. And the figure above shows the results obtained at 40 kW/m2.
All the insulating coatings show positive /'pɔzətiv/ improvement of heat shields. A maximum decreasing of the temperature up to about 200K is recorded along the test.
Moreover, at the beginning, the ablator shows a more effective performance than the one of intumescent paint. While at the end, an inverse phenomenon is observed.
This observation can be explained by the fact that at first 1200 s, both coatings are well adhered /əd'hiə/ to the composite. After that, the ablator are broken and flaked from the composite layer, while the intumescent paint is still remained. For that reason the ablative elastomer loss its protective performance.
Ablator
1200 s
Time (s)
D. Quang Dao et al. IAFSS 11th International Symposium, Paper 149, Feb 9 – 14, 2014
04/05/2018

15. Coating/Composite Burnt-samples
Intumescent/Composite
Ablator/Composite
Before thermal exposure
After thermal exposure
And these are some pictures that show the two coating/composite systems before and after the thermal exposure /iks'pouʤə/ at the heat flux of 75 kW/m2.
We can see clearly that the char layer of the intumescent paint is still adhered to the composite laminate, while the one of the ablative elastomer is broken and detached /di'tætʃ/ from the composite layer.
External heat flux = 75 kW.m-2
D. Quang Dao et al. IAFSS 11th International Symposium, Paper 149, Feb 9 – 14, 2014
04/05/2018

16. Concluding Remarks
The presence of carbon fibre  a worse thermal resistance of epoxy/carbon composite.
Both the Coatings ensure a good protective performance in a minimum of the first 400 s of thermal exposure.
The ablative elastomer  a better protective performance than the intumescent paint at low temperatures.
The charring ablator  broken/flaked from the composite layer at high temperature  Loss of thermal protective performance  Thermal damage of the composite.
The intumescent paint  well bonded to the composite surface  ensures its desired thermal protection
+ For conclusions, the thermal decomposition tests in ISO cone calorimeter have been investigated in this study. We see that the presence of carbon fiber in the composite /'kɔmpəzit/ tents to a worse /wə:s/ thermal resistance.
+ Both of two insulating coatings, that are exanimated as fire protective coating for hydrogen composite cylinders, ensure /in'ʃuə/ a good protective performance in a minimum of the first 300s of thermal exposure /iks'pouʤə/.
+ The ablative elastomer shows a better protective performance than the intumescent paint at low temperature. However, at higher temperature the charring ablator is broken and flaked from the composite. And this induces a loss of the thermal protective performance, and so the thermal damage of the composite.
+ While the intumescent paint are well bonded to the composite surface and so ensures its desired thermal protection.
D. Quang Dao et al. IAFSS 11th International Symposium, Paper 149, Feb 9 – 14, 2014
04/05/2018

17. Thank you for your attention
Contact: Duy Quang DAO
Thank you for your attention.
04/05/2018