Technology Status of Hydrogen Road Vehicles

! Take cryogenic precautions.
! Detect, control, and extinguish fires.
! Identify and assess hazards.
Linney (1996) is a study of quantified risk assessment techniques in optimizing the safety features of on-board
hydrogen systems. One important conclusion is that, in many real hydrogen leak scenarios, high release
velocities and normal ambient winds overshadow the buoyancy/diffusivity advantages.
A1.3 Recent Safety Analysis and Integral Safety Testing for H 2 Vehicles
For illustration, three projects will be reviewed from which we can extract relevant safety information:
! MAN full-size city bus fueled with LH 2, and now ready for public demonstration
! BMW integral testing in severe accidents with LH 2 tanks
! Urban LH 2 refueling station.
(On-board GH 2 and metal hydride storage is discussed in section A1.3.4.)
A1.3.1 Safety Analysis for MAN LH 2 City Bus
This bus is identified as item 3 in Table 1, which compares the characteristics and performance, if available,
of ongoing demonstrations of H 2 vehicles.
The LH 2 bus is a modified MAN 6-cylinder, 12-liter, natural gas engine, able to develop 140 kW maximum
on H 2 with 8:1 compression ratio; external mixture formation with sequential multi-port injection. When full
the three LH 2 cylinders, accommodated under the bus, contain about 40 kg of fuel, have a total weight of about
300 kg and a volume of 630 liters; they suffer 6% boil-off per day. Ninety-two passengers can be carried in
urban service with a range of 250 km.
MAN engineers have carried out a fairly detailed risk assessment for this bus, in the form of a Hazops study
(a hazards and operation analysis), in which engineering judgment substitutes, to some extent, the detailed
statistics needed for a full-blown probabilistic risk assessment. The Hazops study was carried out in
collaboration with the regulatory authority of Bavaria on the accident scenarios and the countermeasures
needed to guarantee safety.
This approach, based on engineering judgment of possible accident initiators and their development in the
system, was then extended to a worst-case scenario in which logic and engineering judgment are put aside,
and an accident scenario is maximized to identify extreme countermeasures. This scenario is intended to
answer the severest critics of the system’s safety.
The worst case imagined was the rupture of a single tank filled with LH 2.
A1.3.2 BMW Simulations of Severe Accidents with LH 2 Tanks
In the absence of probabilistic risk assessments, or of the more simplified Hazops studies, an approach often
taken to accident analysis is to identify a series of worst-case scenarios, in which the originating cause of an
accident and its logical progression are ignored, and attention is focused on its ultimate consequences.
The tools used can be analytical, if enough differential data are available; more often with a new technology,
an experimental approach is adopted whereby the ultimate event is simulated and the consequences observed
on the component or system. Thus BMW has taken LH 2 tanks of the suppliers Linde and Messer Griesheim,
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