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ventilation, windsails were lowered down all hatches and trimmed. Twelve hours
later the whole of the ship was free from gas, with the exception of the side pockets
containing the bedding. As this area was clearing too slowly, the windsails were
adjusted so as to send a current of air well into the side pockets, but 24 hours later
this area was still unsafe, a benzidine acetate test paper showing a strong blue in
five seconds. The operators, equipped with gas masks, then distributed the beds and
pillows round the sides of the hold so as to give free ventilation, but a further 24 hours
had elapsed before this space could be passed as safe, making the time for ventilation
60 hours.
We learnt from this lesson to avoid packed masses of bedding and, when giving
special treatment to large quantities, to arrange it in staggered formation both for
the purpose of quick treatment and speedy ventilation.
We find it is nearly always necessary to give linen stores 12 to 24 hours
more ventilation than is necessary for other parts of our ships. Quite recently we
had the case of a linen locker which was clear of gas except one shelf holding
50 eiderdowns. A test paper anywhere in this heap showed a deep blue in four or
five seconds. These had to be removed and beaten in the open air before they were
clear. It is always our practice to examine again all such rooms the following day, to
make certain that no residual gas has accumulated if they have been closed up over
night.
We have been frequently asked by Medical Officers questions concerning the
lethal concentration in the atmosphere outside a treated space during the ventilation
period. Normally on the weather side of a ship no trace of gas can be detected,
but on the lee side the atmosphere is highly dangerous for some hours after "opening
out." One well-remembered incident was during the ventilation of one of our largest
vessels after treatment. It was in December, 1928. There was no wind, and the
temperature outside was 38° F.; it was also inclined to be foggy. The ship had been
under 0.7 per cent. concentration HCN for eight hours. All the canvas had been
removed from the ventilators and the door and windows of the upper structure were
all open. The ports of D, E, F, G and H decks were still closed. As there were
no parts of the decks that were safe we went on to the quayside in order to remove
our masks, and were surprised on testing the atmosphere to find it was quite dangerous
even on the quayside. Our tests showed a deep blue in ten to fifteen seconds, to a
depth of six feet from the ground, and 30 feet from the hull along the whole 700 feet
length of quay occupied by the ship in question. For at least one and a-half hours
this area was distinctly unsafe, and prompted us to improve our technique by
arranging to fence off the quayside approaches to vessels under fumigation.
We have already written regarding the care needed in interpreting the Copper
Benzidine Acetate test in very cold weather. The incident which prompted us to
warn you then has been repeated several times since, and can be looked for when the
atmospheric temperature falls rapidly overnight during free ventilation.
One of our very early experiences was the finding of heaps of Zyklon frozen
solid. The material had been dumped in heaps and not spread out evenly, and the
rapid evaporation at the surface of the heap froze the interior. Where the heaps were
still freezing six or eight hours later, the ventilation had little effect, and unless the
frozen and other residues were removed the clearing of such areas was slowed down
considerably. The cure was to make certain that the Zyklon was spread out evenly
to a depth of not more than one inch.
We do not consider that any part of a ship is safe for occupation during the use of
Cyanide in any other part. It was the custom at one time to allow the Officer-inCharge
to occupy his quarters on the boat deck during fumigation, until the ventilation
period commenced. This was altered after the following incident. The putting down
of the gas had just finished, and the usual final "look round" was in progress to
ensure everything was gas tight, when an examination of the Officers' quarters showed
that there was a trace of gas getting in. We at once turned him out, and a careful
examination of the quarters showed the gas to be entering by way of the electric
wiring conduits from the deck below. Had we neglected to test these quarters the
Officer would have slept through the afternoon, probably with fatal results.