The European Community requires a vehicle-level bonfire test for vehicles using
plastic fuel tanks for conventional fuels (ECE R-34, Annex 5). A similar test could
be applied to hydrogen-fueled vehicles. It would test a realistic vehicle with its
complete fuel and safety systems. An advantage of such a test is that the same test
could be applied independent of the hydrogen storage technology (compressed gas,
liquid, or hydride).
There are currently standards for bonfire testing of a bare Compressed Natural Gas
(CNG) tank and its Pressure Relief Device (PRD). This standard is FMVSS 304 in
the U.S. and ISO 15869-1 in Europe. Japan has a similar standard. It requires that a
bare tank and its associated PRD be subjected to a propane flame for 20 minutes. The
tank must either survive or safely vent its contents. No modern composite wound
tank is expected to survive for 20 minutes ? so this is not a tank test but really a PRD
test. The test procedure requires the PRD to be shielded from direct impingement of
the flames ? but the shield is not well specified. If it shields the PRD too well, the
PRD will not activate and the tank will burst. This paper describes the results of a
CNG and a hydrogen tank burst from such tests. The mechanical energy released is
enormous. It is simply unacceptable to allow the tank to burst ? the PRD and venting
system must work. Organizations in the U.S, Europe, and Japan are in the process of
modifying the CNG tank bonfire test for compressed hydrogen storage.
A bare tank with a single PRD is not a good simulation of a hydrogen fuel system
installed in an actual vehicle. There will usually be multiple tanks plumbed together
at either the tank pressure or at the intermediate pressure (after the pressure
regulator). There may be more than one PRD. The tank may be shielded (from
debris) or insulated to protect it from an underbody pool fire. Also the heat transfer
from the simulated pool fire (propane flame) will be very different when mounted in a
vehicle versus the bare tank test. A vehicle-level pool fire test will alleviate these
problems.
It is therefore recommended that the bare tank test be replaced by or augmented with
a vehicle-level bonfire test similar to ECE R-34, Annex 5.
1.