The rescue service receives an alarm one cold December day concerning
an accident in which a tank lorry has been driven off the road into a river.
At the incident site it becomes apparent that the lorry has slid down the
bank into the river and now the greater part of the cab and front section of
the lorry are under water. The driver is sitting with his head above water,
showing no signs of life. The water appears to be deeper further out, which
is a reasonable assumption as the river is fairly wide. The tank is full of
carbon disulphide, which is both poisonous and highly flammable. Full
suits & masks are not carried in the pumping appliance, and the question
is raised as to whether the driver can be quickly removed from the cab and
his life saved. There are no signs of leakage from the tank. The chemical
database tells us that carbon disulphide is heavier than water (density 1260
kg/m³), that it is not easily dissolved in water (0.29 mass% at 25°) and that
its evaporation point is low (21.6 kPa at 5° C). The evaporation point is not
relevant since any leakage will have direct contact with the water in the
river. As its solubility is low and its density high any leakage would remain
compact, sink to the bottom and move out to deeper water. Consequently,
any leakage under water would not mix with the air, and it is reasonable to
assume that the cab of the vehicle is not affected by any possible discharge.
This makes the task of wading out to the cab to remove the driver relatively
safe, even if the tank is leaking under water. As a safety measure, though,
the task should be carried out on the upstream side of the vehicle.
Example 12