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bromide, ethylene oxide-carbon dioxide mixtures, sulfuryl fluoride,
and certain other fumigants in ounces per 1,000 cubic feet (milligrams
per liter). Concentrations of phosphine and some other fumigants
cannot be measured with a T/C unit. However, they may be measured
with detector tubes. Residual gas concentrations during aeration of
commodities or enclosures can also be determined for most fumigants
with detector tubes.
Principles of Operations
Special pumps are used to draw a measured sample (usually 100
milliliters) of an air-gas mixture. The sample is drawn through one or
two detector tubes where a chemical reaction with the tube reagent
takes place, creating a stain. The length of the stain is proportional to
the concentration of the gas. Measurement of the length of the stain is
made using a calibrated chart or by simply reading the number from a
scale printed on the glass tube.
Gas detector tubes are manufactured with a constant reagent weight
with corrections for variations in the diameter of each tube. Detailed
operational instructions accompany the equipment.
The detector tubes are specific for each fumigant and usually are
available from several manufacturers. However, it is advisable to use
the pump supplied by the manufacturer of the tube used. In an
emergency, detector tubes available under the trade names of Auer,
Draeger, Gastec, Kitagawa, and Mine Safety Appliances can be used
with pumps manufactured by any of these companies provided they
draw 100 ml. Adapters may be necessary because of the different
diameters of the tubes sold by each manufacturer. The Kitagawa
pump uses a removable, stainless-steel micro-orifice to reduce the rate
of air flow through many of their detector tubes. This is to provide
greater accuracy in the chemical reaction within the tube. The orifice
should be removed when using tubes manufactured by other
companies.
Equipment
Detector Kits or Gas Samples
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PPQ
Tubes should be stored under refrigeration to increase shelf life.
Before each day’s use, pumps should be tested as provided by
instructions with each kit and repairs made as necessary. Spare parts
and operational instructions should be kept with each kit for use as
needed.
When many samples must be drawn to a common point during a large
fumigation, an auxiliary pump can be used. If only one sample lead is
involved, it may be necessary to pull the fumigant through the line by
pumping several times. A used tube can be inserted in the pump to
determine when the fumigant has reached the pump.
Volatilizer
It is desirable to pass some fumigants through a vaporizer to assure
volatilization at any temperature below 60°F or when large quantities
(i.e., a total amount of 5 pounds or more of methyl bromide) are
required. The volatilized fumigant should be introduced into or near to
the air flow of the blower or fan. A simple volatilizer can be made with
a 25-foot coil of 3/8 inch O.D. copper tubing immersed in a container
of hot water. For use with amounts greater than 5 pounds of methyl
bromide, 50 feet of 1/2 inch O.D. copper tubing can be coiled in a
large container of water which has been heated to temperatures of
150°F or above.
Equipment
Detector Kits or Gas Samples
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PPQ
The fumigator should be warned that the fumigant should be
introduced through the tubing at the rate of 3 to 4 pounds of gas per
minute. The gas introduction tube should feel hot to the touch as a
good measure of satisfactory vaporization.
The volatilizer should be made of semihard copper tubing. It is important that gas be
introduced and discharged as shown by arrows. If applied in reverse order, it may
move so rapidly that some liquid will pass into the chamber.
FIGURE 8-1-3: Methyl Bromide Volatilizer Coil
Equipment
Air Velocity Measuring Instruments
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PPQ
Air Velocity Measuring Instruments
Anemometer
The cubic feet per minute (cfm) of a fan can be approximated by use of
an anemometer or other wind measuring device. Measurements of air
movement are taken 12 inches from the face of the fan to be tested. A
minimum of three readings should be taken; one from the center and
the others from points toward the outside of the fan. Readings are
then averaged. If an anemometer is used, each measurement should
be for 1 minute, thereby giving the result in feet per minute. If a wind
FIGURE 8-1-4: Liquid Fumigant Vaporizer
Equipment
Air Velocity Measuring Instruments
06/2004-01 Treatment Manual 8-1-27
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