cloud covered a town or city, its
almost inevitable ignition would
cause widespread destruction.”
Although elaborate safety
precautions have been proposed to
minimize the chance of a large
LNGspill, such an accident could
still take place. Spills might result
from storage tank ruptures, ship
collisions, or leaks on land orat
sea. They could occur during
transfers from ships to storage
tanks or during pipeline transfer on
land. Because of the large chemical
potential energy associated with
the fuel in liquefied form andi its
ability to form a large cloud of
vaporrapidly, anyspill is potentially
dangerous. Thus,it is vital to ex-
plore the possible consequences of
such spills and how to minimize
adverse effects.
When we began our research,
existing models disagreed by over
an order of magnitude on how far
the vapor cloud from a particular
large spill would travel downwind.
There was also very little previous
work on scaling relationships that
would allow us to extrapolate from
the results of small experiments to
full-scale effects. There was no existing facility at which we could
safely carry out large experimental
LNG spills under the conditions
necessary to validate our numerical
models.
Since mid-1978 we have participated in a series of spill experiments at the Naval Weapons
Center, China Lake, Califormia,
primarily to evaluate instruments
for the larger spill experiments we
plan, but also to gather data that
can be used to improve our predictive ability. The first four of these
tests involved spills of 5 m° of LNG
each and produced vapor clouds
that were warmer, extended
farther, and contained regions
more enriched in the heavier (and
more detonable} hydrocarbons
than expected. We are now
engaged in series of 40-m? spill
experiments at China Lake {using
the instruments and data-gathering
techniques derived from the
previous experiments) to further
improve our models and refine our
techniques for even larger experiments.
We began our experimental
program with 5-m° spills because
an existing facility at China Lake
was amenable to such tests and
because spills of this size were adequate to evaluate the performance
of gas sensors in the field. We
realized that these tests would not
be large enough to permit observation of all important phenomena
associated with the dispersion of
large clouds of natural gas, but
there was the possibility that such
experiments would teach us
something new about the process.
Experimental array and
instrumentation
Figure 1 shows the instrument
array used in our 5-m° spill experiments. The array consisted of eight
primary stations distributed down-
wind from the spill point, each one
28
equipped with a variety of grab
samplers, gas sensors, and ther-
mocouples (points 1 through 8).
The primary stations were supplemented at points 9, 10, and 11
by anemometers and at point 12 by
a Jet Propulsion Laboratory (JPL)
gas sensor. There was also a
LIDAR (laser radar} systern fielded
by Computer Genetics Corporation and a 12-point square array of
Mine Safety Appliances (MSA) gas
sensors (not shownin the figure).
Cables connected each instrument
station to power sources and the
data-acquisition trailer. The main
function of the grab samplers. gas
sensors, and thermocouples was to
measure the concentration of the
LNG vapor in various ways at
various locations.
The grab samplers consisted of
evacuated bottles that were opened
at prescribed intervals to collect a
sample of gas for later analysis by
mass spectrometer to verify the
performance of our gas sensors.
The Shell gas sensors(stations 1
and 2), developed and loaned to
us by Shell Research Ltd., of
England, measured heat loss from
a heated filament exposed to the
gas stream. The TSI sensors (siations 3 and 6), manufactured by
Thermo-Systems, Inc., of St. Paul,
Minnesota, operated by forcing the
gas through a sonic nozzle and
measuring, with a thin-film
anemometer, the flow velocity
(which depends strongly on gas
composition}. The infrared gas
analyzer (station 4), custom-built
for us by Anarad, Inc., was capable
of distinguishing methane, ethane,
and propane. It gave us ourfirst
quantitative evidence of differential
boiloff of the different hydrocarbons froin the liquid pool.