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During a fumigation, you may use tubes containing Ascarite® to
remove carbon dioxide from gas samples. Used filtering material
should be discarded. The Ascarite® tube should be connected between
the Drierite® tube and the sample inlet. In no instance should Drierite®
and Ascarite® be mixed in the same tube. Ascarite® should be replaced
when the granules begin to aggregate or become moist.
Equipment
Fumiscope and Gow-Mac
8-1-4 Treatment Manual 06/2004-01
PPQ
It is always advisable to use Drierite® when taking concentration
readings of SF, MB, or CB. Desiccant should be fresh and frequently
changed to ensure correct readings. Never use Ascarite® when making
readings of SF because a chemical reaction will occur. Never use
Ascarite® when taking readings of CB because carbon dioxide gas is an
integral part of the reading to be obtained.
Standardizing the Instrument
Standardizing the instrument is the first and basic operation. Do the
following to standardize the instrument.
1. Connect the instrument to an electrical outlet with proper voltage
and set the pump and meter switches to “on.” If inoperable,
check fuse. (Replacements—Little Fuse or Buss #3AG 1/2
Amp.—should be kept on hand.)
2. Attach the drying tube to the inlet port. The instrument should
be given a tightness test. This can be accomplished by placing a
finger over the inlet of the drying tube. The flow ball in the flow
meter should then fall to zero if the tubing and connections are
tight.
3. Warm up the instrument for 15 to 30 minutes.
4. Adjust the gas flow rate to 1 cubic foot per hour (CFH) by
adjusting the flow rate knob. If the flow rate knob is turned
counter clockwise too far, the pump will emit noises and cease to
operate properly. When properly adjusted, the flow ball should
float at the center mark or slightly below on the calibrated glass
cylinder. Slight fluctuations from a stationary position may
occur. Dry, fresh air is now being drawn through the T/C cell by
means of the pump, the air entering via the inlet on the face of
the instrument, passing through the cell, and leaving through
the exhaust outlet.
5. Turn the zero adjustment knob to obtain a zero reading on the
meter. Several additional adjustments during the first few
minutes may be necessary to obtain a stable zero reading. A
check of the meter needle should be made periodically to
determine if there is any sticking of the needle. A check is done
by slowly turning the adjustment knob clockwise. A clockwise
turn will swing the needle from 0 to 100/200 on the meter scale.
A counterclockwise twist will return the needle to zero.
Standardization is now complete and readings can be made of
fumigant-air mixture drawn through the unit. It may be necessary to
replace the desiccant at this point.
The difference in the thermal conductivity of the fumigant-air mixture
as compared with fresh air is measured electrically and indicated on
the meter as concentration readings in ounces of MB per 1,000 cubic
Equipment
Fumiscope and Gow-Mac
06/2004-01 Treatment Manual 8-1-5
PPQ
feet. T/C units used in PPQ must be calibrated for MB by the
manufacturer or an outside contractor prior to use. You will not get
accurate readings when fumigations are under even a small vacuum.
The Gow-Mac® T/C units used by PPQ are equipped to measure MB
concentrations up to 400 ounces per 1,000 cubic feet. Since the T/C
unit’s galvanometer responds linearly to gas concentrations, the MB
calibrated instrument may be used for measuring certain other gases
by the use of specific multiplication factors determined for each
instrument.
Operational Procedures
The proper use of the Fumiscope® is discussed under two headings:
◆ Selecting Operational Site for the T/C Unit
◆ Measuring Gas Concentrations With the Standardized Unit
Because of the variety of fumigation situations, some adjustments
may be necessary to meet specific needs. Nevertheless, this outline
should be helpful in establishing correct operational procedures.
Selecting
Operational Site
for the T/C Unit
The T/C unit should be close enough to the fumigation site to avoid
the use of unreasonable lengths of sampling tubes, to allow for
constant surveillance of the fumigation during testing, and to avoid
interference with other activities in the area. It should be at a
sufficient distance from the fumigation site (at least 30 feet up-wind)
to allow the operator to function without the fear of accidental
exposure to gas and to allow for easy exit in an emergency. Excessive
　
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