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gas distribution. Take the initial concentration reading 30 minutes
after all the gas has been introduced.
When evacuating large cylinders, getting the final amount of gas out
may take a long time. Consider taking a T/C unit reading 30 minutes
after the gas was first introduced. If the gas distribution is even (all
readings within 4 ounces of each other) and at a significantly high
concentration, then turn off the fans. Running the fans longer may
contribute to gas leakage. Allow the remainder of the gas to discharge
with intermediate running of the fans. Normally, all the gas should be
introduced within 30 minutes.
Step 2—Testing for Leaks
Wear the SCBA while checking for leaks. Use a halide detector to test
for leaks before the 30 minute reading or anytime when the
concentration level is unknown or above 5 ppm. Test around the
perimeter of the container, and especially at the plugged drainage
holes. When you detect leaks, have them sealed using tape.
If you detect excessive leakage (concentration readings of 50 percent
or less of the minimum concentration) in a container which cannot be
corrected in a practical way, do not attempt to correct the problem by
adding more gas. Quickly evacuate the remaining gas from the
enclosure, eliminate the problem, and construct a new enclosure.
Aerate as usual following procedures on page-2-8-14. Restart the
fumigation in the new enclosure.
Don’t touch the introduction line with your bare hands—you could get burned!
Close the cylinder valve once the proper dosage has been introduced.
Do not begin counting fumigation time until all the gas has been introduced
and valve on the MB tank is closed.
Chemical Treatments Fumigants • Methyl Bromide • Special Procedures for Container Fumigations Without a Tarpaulin
Conducting the Fumigation
2-8-14 Treatment Manual 10/2002-04
PPQ
Step 3—Taking Concentration Readings
Take concentration readings with a T/C unit to determine the gas
concentration and distribution within the enclosure. Check desiccant
tubes before each reading and change Drierite® if its color is pink.
Depending upon the length of exposure period, take concentration
readings at the following times:
◆ 30 minutes
◆ 2 hours
◆ 4 hours (optional)
◆ 6 hours (optional)
◆ 12 hours (optional)
◆ 24 hours5
◆ 36 hours (optional)
◆ 48 hours
◆ 72 hours
Any final concentration reading (see following example)
EXAMPLE: If the treatment schedule lists a 6 hour exposure period,
then the 6 hour reading would be required and not optional as shown
in Step 3. If the treatment schedule lists a 16 hour exposure period,
you must take a 16 hour reading.
Commodities used for food or feed may not be re-treated. If commodities fall
into this category, the only options are the following:
◆ Re-exported to another country if they will accept the shipment
◆ Destroy by incineration
Important
Before obtaining readings, always purge sampling lines with a mechanical or
hand pump. If you’re using treatment schedule T101 or T104-a-1 to fumigate
fresh fruit or vegetables, see “Special Procedures for Fruits and Vegetables”
on page-2-4-25.
5 If fumigating oak logs or lumber for export, see “Special Procedures for Adding Gas to Oak Logs and Lumber.”
Avoid using hand-held two-way radios near the T/C unit. Using two-way radios
near the T/C unit will interfere with an accurate concentration reading.
Chemical Treatments Fumigants • Methyl Bromide • Special Procedures for Container Fumigations Without a Tarpaulin
Conducting the Fumigation
10/2002-04 Treatment Manual 2-8-15
PPQ
Thirty Minute Reading
The 30 minute reading shows the initial concentration and
distribution of gas. The 30 minute reading can indicate leakage,
sorption, incorrect dosage calculation, or error in fumigant
introduction—all of which require immediate attention. Concentration
readings should not differ more than 4 ounces among the leads.
Two Hour Reading
In comparison with the 30 minute reading, the 2 hour reading also will
indicate if the container is leaking or the commodity is sorbing gas.
Readings more than 15 percent lower than the 30 minute reading will
require close monitoring and possible corrective action.
EXAMPLE: Your dosage for the fumigation was 4 pounds (64 ounces).
The 30 minute reading was 50 ounces (3.125 pounds). The 2 hour
reading is 42 ounces (2.625 pounds). The 2 hour reading is more than
15 percent less than the 30 minute reading and would indicate that
either a leak or sorption problem may exist. You would need to
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