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The gas is heavier than air, consequently heavy concentrations are often found at
floor level in the early stages of a treatment. However, the gas is not difficult to disperse
after an operation.
Apart from this density effect, the gas has greater powers of penetration than most
other fumigants in common use and this applies not only to penetration into commodities
but also through walls and sealing materials. A high standard of maintenance and sealing
is necessary in rooms to be used for fumigations using methyl bromide.
The penetration powers of methyl bromide, the absence of smell, the lack of immediate
symptoms of poisoning and the long term effect of poisoning, make it essential that
adequate precautionary measures should be taken at all stages from the manufacture of
the fumigant to the declaration of freedom from danger at the conclusion of operations.
The precautionary measures and the additional precautions for the treatments of ships
which are to be followed are laid down in a Home Office Pamphlet dated 1960.
The fumigation of ships by methyl bromide, usually tor disinsection purposes, occurs
only occasionally in the Port of London.
The exposure to the gas depends on the concentration and on the period and purpose
of the exposure. For example in the case of a ship with completely empty holds, 12 ozs
of liquid per 1,000 cu. ft. for 12 hours would eradicate a rodent infestation in the holds,
whereas a minimum concentration of 32 ozs per 1,000 cu. ft. for 24 hours would be
required in the case of Khapra beetle infestation.
The following are the names of the firms approved for carrying out the deratting of ships:—
Contra-Pest Service Ltd.
Rentokil Laboratories Ltd.
(iv) Progress in Rat Proofing of Ships
Lloyds Register of Shipping Statistical Tables 1970, show the ocean fleets of the World to
be comparatively new, that is 57% are less than 10 years old. The introduction of rat proofing
measures in ships first adopted by the Maritime nations some twenty years ago has become
standard practice over the years and rat proofing of the vulnerable parts of the ship, for example
the provision store room, is now almost always present. When the rat proofing is found to be
defective, usually through non-replacement after refit, every endeavour is made to have it made
good before the vessel sails.
RODENT CONTROL MEASURES CARRIED OUT ON LIGHTERS
Rodent control measures on lighters have been carried out successfully during the past year.
Of the 3,545 lighters inspected for rodent indications, 2,707 were inspected on the Upper and
Middle River Districts, the remaining 838 inspections being carried out in the respective dock
groups.
It will be noted by referring to the attached table that the degree of infestation is still
decreasing. The following figures are very encouraging. Of the 3,545 lighters inspected 93.6%
were found not to have any rodent evidence at all. Only 177 rats were recovered after treatment
of the remaining lighters and the average rats recovered per lighter treated was 1.9.
The methods of de-ratting employed throughout the year were:-
Fumigation Rodenticides
1. Sulphur Dioxide. 1. Sodium mono-fluoroacetate
2. Methyl Bromide 2. Multiple dose poisons
3. Ethylene Oxide, + Carbon Dioxide.
The method of treatment is determined by the condition and degree of infestation of the
lighter at the time of inspection. In view of the fact that in nearly all instances there is a residue
of water and foodstuffs in lighters when empty, from past experience it has been found that if
treatment is required it is far more efficient to fumigate than use a rodenticide.
Throughout the year, 334 lighters were fumigated with Methyl Bromide for insect control of
the commodity. As the dosage required varies from 20 to 30 ozs per 1,000 cu. ft. according to the
species of insect pest present, the chemical properties of the mentioned fumigant and the 24 hour
exposure period required for Methyl Bromide are more than adequate to destroy any rats that may
he present in the lighter at the time of fumigation.
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