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leads with the use of a Mityvac hand-held pump (for supplier, see Vacuum
Pump, Appendix H):
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 psig 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.)
The acceptable air concentration level for methyl bromide (MB) is 5 ppm. A
respirator (approved SCBA or MSHA/NIDSH) is required if the MB
concentration level in the air is greater than 5 ppm at any time. You and the
fumigator must use your SCBA while introducing the gas, checking for leaks,
and when taking aeration readings.
Chemical Treatments Fumigants • Methyl Bromide • Tarpaulin Fumigation
Conducting the Fumigation
2-4-20 Treatment Manual 03/2004-05
PPQ
are being introduced per minute. The water temperature in the
volatilizer should never go below 150 °F at any time during gas
introduction. The water in the volatilizer may include an antifreeze
and should be handled with the appropriate safeguards.
The fumigation time begins once all the gas has been introduced.
Record the time gas introduction was started and completed in Block
32 on the PPQ Form 429. Run the fans for 30 minutes to achieve even
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 tarpaulin on the floor, corners, and especially where
electric cords, gas sampling tubes, or gas introduction lines are
present. When you detect leaks, have them sealed using more sand or
sand snakes for floor leaks and tape for sealing small holes in the
tarpaulin.
If you detect excessive leakage (concentration readings of 50 percent
or less of the minimum concentration) in a tarpaulin 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-2-2-3. 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.
Important
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 • Tarpaulin Fumigation
Conducting the Fumigation
03/2004-05 Treatment Manual 2-4-21
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:
　
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