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◆ Observe time for pressure to recede from 25 to 2.5 mm in the
open arm
The time lapse for the chamber pressure to recede from 25 to 2.5 mm
in the open arm must be 22 or more seconds for minimum approval.
Chambers shall be reinspected every 6 months when 22 to 29 seconds
are recorded. Chambers which retain the pressure for 30 seconds or
longer should be tested annually. (Chambers used for fumigating
cherries for export to Japan are required to meet a higher
standard—the time lapse for the chamber pressure to recede from 25
to 2.5 mm must be 60 or more seconds for minimum approval.)
Inability to develop or maintain adequate pressure indicates
considerable leakage. In such cases, the chamber operator may use a
smoke bomb or other device in an effort to determine the areas of
leakage.
Equipment
Vacuum Pump
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Electronic manometers are also available and may be used in lieu of
the Open-arm (U-tube) type.
Vacuum Pump
Mityvac Hand-Held Vacuum Pump
The Center for Plant Health Science and Technology has developed the
following procedure to detect blocked monitoring leads with the use of
a Mityvac hand-held vacuum pump (for supplier, see Vacuum Pump,
Appendix 8):
FIGURE 8-1-6: Open-arm Manometer
Equipment
Phosphine Detector
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Usage
1. Prior to fumigant introduction, connect the Mityvac hand-held
vacuum pump to a monitoring lead.
2. Squeeze the handle on the Mityvac Unit. If the lead is blocked, a
vacuum will be indicated on the vacuum gauge of the Mityvac
unit. (The handle should be squeezed two or three times for
monitoring leads longer than 25 feet. The Mityvac hand-held
pump has the capacity to attain and hold 25 inches of Hg
vacuum and a minimum of 7 psi pressure.)
3. Disconnect the Mityvac hand-held pump from the monitoring
lead, and repeat this procedure for each monitoring lead.
(Connect monitoring leads to the gas analyzer prior to fumigant
introduction.)
Phosphine Detector
PortaSens Phosphine Detector
Description Historically, phosphine measurements have been done using detector
tubes specific for phosphine (see Detector Kits or Gas Samplers in
this section). The high cost associated with these tubes have been a
deterrent for many ports.
A more accurate, portable unit has been recommended for usage
during phosphine fumigations. The Series B16 PortaSens is a
portable, battery operated instrument for the measurement of various
gas concentrations in ambient air. The instrument can be ordered
specifically for phosphine in the 0-1,000 ppm range. Ranges from 0-1
ppm are available also, along with other configurations. The PortaSens
is a complete measuring instrument containing an electrochemical
sensor, sampling pump, flow cell assembly, microprocessor
electronics, and a two line backlit LCD display. The unit is powered by
a rechargeable NiCad battery located in the handle, with the charger
connection located at the bottom of the handle.
Operation The PortaSens needs to be calibrated by the Center for Plant Health
Science & Technology (CPHST) before usage. After calibration, the
instrument is ready to use directly out of the box. Simply remove the
instrument from the storage case and press and release the button
(instrument switch) on the front of the handle. The LCD display on the
front will immediately be activated and the internal pump will begin to
pull sample into the flow cell.
Equipment
Phosphine Detector
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The unit comes with a flexible extension wand that screws into the
standard inlet fitting. Connect the extension wand and a length of
flexible tubing that will reach safely from the item(s) being fumigated
to the PortaSens.
Response Time Response time will vary depending on the gas concentration and
ambient temperature. The LCD readout will stabilize when maximum
concentration is reached. Readings will be more timely when the
monitoring leads are purged using the Mityvac hand held vacuum
pump (refer Mityvac Hand-Held Vacuum Pump).
Alarm Function The PortaSens contains both visual and audible gas concentration
alarm functions that are preset at the factory. Refer to B16 PortaSens
Operation and Maintenance Manual for specific instructions. For
instruments in the 0-1,000 ppm range, the alarm has been disabled to
allow for more efficient usage.
Battery Power
Supply
The instrument is powered by a rechargeable NiCad battery. With a
fully charged battery, the unit will operate continuously for 12 hours
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