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V.—Is Sulphur Dioxide the most suitable gas to use in fumigation?
VI.—Is 1 lb. of sulphur burned in each 1,000 cubic feet sufficient for disinfestation?
VII.—Is a four-hour closure of spaces under S02, as a minimum, sufficient for
disinfestation?
VIII.—Given an atmosphere of S02 from 1.5 to 3 per cent, in a hold, has the method
of production, whether by machine or burning-pot, or candle, or from condensing bottle, any
special significance with regard to rat destruction?
Inspection :—
IX.—What methods of inspection and what indications should guide in the conclusion
that a ship needs disinfestation?
X.—Is it desirable that, with a view to securing to the shipowner the most convenient
moment for disinfestation, information as to the necessity for disinfestation be a matter of
intercommunication between Medical Officers of Health?
The following report was made to the Association :—
9th October, 1919.
RAT ENQUIRY.
I have pleasure in reporting on the Enquiry made at the request of Medical Officers of
the Association, as follows :—
Sixty-three lists of questions were sent out. Answers were received from 23 Medical
Officers including those of all the larger ports in England. The questions were mostly leading
questions and could be directly answered in few words, but the comments kindly made are of
large interest.
I have to regret that the Scottish ports were not circularised.
(1) There is agreement that the powers conferred under the Food Orders are useful in
dealing with rats on ships.
(2) And that permanency should be given in some way to such Orders as a measure of
Public Health.
(3) There is also complete agreement that trapping and poisoning of rats is only auxiliary
to fumigation as the proper method of disinfestation of ships. A proper supervision of the
fumigation is emphasised in some of the answers.
(4) Those who from experience could answer Question 4, were unanimous that the most
satisfactory time for disinfestation was immediately on complete discharge of cargo.
(5) Sulphur dioxide gas is in evident favour as a fumigant in all the ports; in the words
of the Medical Officer of Health for Liverpool: " It is economical, free from risk to human life
and efficient when used in proper quantity." I myself have always felt unable to accept the
heavy responsibility for danger to life accruing in the use of any very lethal gas or one which
does not announce its presence to the unwary; in practice, many people are about during the
fumigation of a ship.
(6) Opinion was divided on the question of the efficacy of 1 lb. of sulphur burned in
1,000 cubic feet. The more general practice is the burning of 2 lbs. to 3 lbs. of sulphur per
1,000 cubic feet. Some Medical Officers are satisfied with the 1 lb.
(7) As with the amount of sulphur burned, so with the time of action to be allowed, opinion
was divided and the general practice is a longer exposure—six, eight or more hours. Some
answers, though agreeing, emphasised the minimal nature of the four hours suggested in the
question.
i'8) Answers as to the methods of production of the sulphur dioxide atmosphere show that
however produced the 1.5 to 3 per cent, atmosphere of sulphur dioxide is efficient, and that
the method of production is immaterial.
Some suggestive remarks made in the answers to Question 8 are the following
(0) " The question is one of rapid development; the quicker a space is filled with gas the
more efficiently the work is done."
This would imply for sulphur pots and candles and for condensing bottles as wide
a distribution of fumigating units over the space to be fumigated as is possible.
(b) . . the disinfestation must be immediately commenced after the cargo has been
got out on account of the rats transferring their quarters . . ."
This implies that food stores, pantries, living quarters, chain lockers and peaks should
be under fumigation simultaneously with the holds, and urges the necessity of
immediate disinfestation.
I would add a suggestion of the proven utility of a deck search—boats, steampipecasings,
winch barrels, &c.—while the ship is under fumigation.
(c) " Burning pot or candle quite satisfactory."
(d) " Condensing bottle found quite effective."
(e) Up to the 3 per cent, concentration we employ, the method of production is
immaterial."
(/) " Condensing bottle best."
(g) " The methods used are burning candles, 21 lbs. to 1,000 feet, and Boake.
Boberts & Co.'s " Sulphume " cylinders, which are simple, reliable and efficacious."
One ounce of liquid is evaporated in 50 cubic feet. This is stated to produce
1.55 per cent. gas.
(h) The machine is most efficient."
(1) The burning pot is quite satisfactory, and can be left alone to do the work."