226 COMMISSION ON THE FUMIGATION OF SHIPS
air drawn from small spaces in the volumes required for bringing
samples into the testing chamber is sufficiently large to set up
currents from the hold ; (b) that the rubber tubes may absorb
some of the HCN; (c) that the determination of concentration is
based on a colour change, the appreciation of which may vary with
different operators; and (d) that the test-papers deteriorate,
particularly when exposed to light.
It should be possible to devise some more exact method capable
of being used on a ship’s deck and, in our opinion, efforts should
be made in that direction.
(Ill) Speaking generally, we are agreed that the use of a warning
gas mixed with the hydrogen cyanide is advantageous, though none
of the mixtures so far employed are completely satisfactory.
Cyanogen chloride possesses high lachrymatory effects, but is only
used in practical fumigation when generated by the barrel method.
Thus generated, however, the corrosive effects of the gas have to be
taken into account. A mixture of 20 per cent liquid CNC1 and
80 per cent liquid HCN has been employed, but its use has been
discontinued.
In American practice, the addition of 10 per cent chloropicrin
to liquid HCN and 5 per cent to Zyklon B, or 3 per cent chloro¬
picrin and 2 per cent brom-acetic ester, have been found suitable
and are considered to afford protection to the fumigating crew whilst
introducing the gas, as well as to give warning to others in some
cases. There is no evidence that, used in those amounts, the warning
gas has any deleterious effects; but whether it penetrates to the same
extent as HCN is open to question.
The possibility of first dosing the compartments with a warning
gas before the actual fumigant is introduced was considered; and,
whilst it was agreed that, with loaded ships, such a method would
have certain advantages, it would necessarily complicate the process
of fumigation, which, for practical applications, should be as simple
as possible.
For the protection of the fumigating staff and the crew of the
ship, in some countries special precautions are taken, such as the
provision of oxygen-inhalation apparatus, specific respiratory and
circulatory stimulants, life-lines and warning signs on all doors of
rooms under fumigation. In the United States of America, as a