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positioned.
Circulation
Fans are necessary to distribute SF and to help prevent condensation.
The number of fans depends upon the cubic volume of the enclosure
being treated, and the arrangement of cargo. Axial fans of
approximately 5,000 cfm have proven effective. Usually two fans are
used, one on either end facing the lower center and upper center of the
load. If the enclosure is over 35 feet long, additional fans should be
used. It is usually not necessary to run fans longer than 15 minutes
after the gas has been introduced.
Prevention of Condensation
In cool weather, moisture may condense under tarpaulins if the sun is
shining directly on the load. Continuous air circulation can prevent
this from occurring. Do not tarp or seal any item while it is wet.
Gas Sampling Lines
A thermal conductivity unit calibrated for Vikane must be available for
readings. Sampling lines should be arranged so that gas samples are
drawn from representative parts of the fumigation area and lead to a
common point.
A minimum of three sampling lines should be placed in enclosures of
up to 10,000 ft3 at the following locations:
◆ Front of the load, 3 inches from the floor
◆ Center of the load, midway from the bottom to the top of the load
◆ Rear of the load, at the top.
When 10,000 to 15,000 ft3 are being treated, two additional lines
should be appropriately deployed.
Chemical Treatments Fumigants • Sulfuryl Fluoride
Tarpaulin Fumigation
2-9-4 Treatment Manual 10/2002-04
PPQ
Gas Introduction
Unlike methyl bromide, SF does not require the use of a volatilizer to
speed up its conversion from a liquid to a gas. The gas introduction
tube should be placed directly in the air flow of a fan away from the
cargo. Also, place a drip cloth under the tube. The introduction rate is
controlled by the introduction line length and diameter. A 1/8 inch
inside diameter by 100 ft long hose will allow a flow rate of
approximately 2 lbs per minute while a 25 ft long hose will allow
approximately 4 lbs per minute.
Approximate; dependent on pressure in cylinder.
It is important not to overshoot the ability of the fan to rapidly disperse
the cool air near the fumigant introduction site. Fan capacity should
be at least 1,000 cfm for each lb of Vikane introduced per minute. In
addition, a volatilizer (heat exchanger) may be used in fumigating
containers or small chambers to prevent a “fog-out” (condensation)
which could cause corrosion or damage to the contents. The last few
pounds of fumigant will turn to gas within the cylinder before moving
out, and the flow rate will be reduced. The cylinder and tubing will
often become frosted. Be certain that no open flame or glowing hot
surfaces above 400 °C are present since corrosive substances (mainly
hydrofluoric acid) are formed when SF is exposed to such conditions.
To avoid possible damage, do not apply the fumigant directly to any
surface.
TABLE 2-0-30: Effect of Hose Inside Diameter on Rate of Gas Introduction through a
25 Foot Hose
Inside Diameter (in inches) Pounds Vikane Per Minute
1/8 4
1/4 20
1/2 45
TABLE 2-9-1: Effect of Hose Length on Rate of Gas Introduction through a inch
Inside Diameter Hose
Hose Length (in feet) Pounds Vikane Per Minute
25 ft 4.0
50 ft 2.8
100 ft 2.01
1 Where fumigant introduction rates lower than 2 lbs/min are needed, a longer hose can
be used, e.g., 200 ft.
1⁄8
Chemical Treatments Fumigants • Sulfuryl Fluoride
Tarpaulin Fumigation
10/2002-04 Treatment Manual 2-9-5
PPQ
Dosage Rate
To control a particular pest, locate the proper fumigation schedule to
be followed in the Treatment Manual. The three variables in these
schedules are temperature, dosage, and exposure duration. Treatment
is not recommended below 50 °F. Dosages are in pounds per 1,000
feet3 of space. To determine the total amount of fumigant required by
weight in pounds, divide the total volume of space by 1,000. Then
multiply the resulting figure by the dosage rate schedule expressed in
pounds (per 1,000 feet3). The cylinder should be placed on a scale, and
the flow of gas is controlled by the valve and introduction line until the
desired cylinder end-weight is obtained. The valve should be turned
fully open to fill the fumigant introduction hose with liquid SF.
Initially, the valve should be opened slightly until flow has begun and
then opened about one full turn which should give full flow through
the 1/8″ fumigant introduction hose.
Measure Gas Concentrations
During the course of fumigation, minimum concentrations must be
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