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10/2002-04 Treatment Manual 6-3-1
PPQ
Treatment Manual
6 Certifying Facilities 1
Certification of Atmospheric
Fumigation Chambers
Contents
Construction and Performance Standards page-6-3-1
Discussion (Overview) page-6-3-1
Basic Elements for Design and Construction of Chambers page-6-3-2
Gas-Tight Construction page-6-3-3
Circulation and Exhaust Systems page-6-3-3
Fumigant Dispensing System page-6-3-4
Pressure-leakage Test for NAP Fumigation Chambers page-6-3-4
Other Auxiliary Equipment page-6-3-5
Construction and Performance Standards
Discussion (Overview)
The primary purpose of a program fumigation is to obtain quarantine
control of the pests in all stages of development in or on the product
being fumigated. A properly constructed fumigation chamber will
provide an enclosure into which the product can be loaded and where
the fumigant will be maintained at the prescribed concentration for
the required exposure period.
The primary consideration in the construction of an atmospheric
fumigation chamber is to make it as gas tight as possible. In addition,
circulation equipment must be installed to distribute the fumigant
properly throughout the chamber. The chamber must retain these
qualities of tightness and fumigant circulation during every
fumigation.
Although chamber sizes are not restricted to specific dimensions,
chambers should be sized according to the volume of material to be
fumigated. Experience has shown that two moderately sized chambers
would be preferable to one large facility.
The construction material may be selected according to the type of
product to be fumigated and the method of operation involved. Wood
construction of wood frame with light metal sheathing could be
utilized if the products to be fumigated are lightweight and are to be
hand loaded. Heavy products often loaded by machinery or
handtrucks would require that the construction be of heavy gauge
sheet metal, masonry, or metal plates. It is advisable to construct the
chamber in the most durable manner consistent with its intended use.
Certifying Facilities Certification of Atmospheric Fumigation Chambers
Construction and Performance Standards
6-3-2 Treatment Manual 10/2002-04
PPQ
Auxiliary equipment will be required to measure, vaporize, circulate,
and exhaust the fumigant. Such equipment should be sized according
to the volume of the chamber. When a relatively small amount of
fumigant is used, it is often measured by volume in graduated
dispensers (MB only). When larger amounts are used, the fumigant is
most often measured by weight.
For the fumigant methyl bromide (MB) a volatilizing unit through
which the fumigant passes is located outside the chamber.
For the fumigant sulfuryl fluoride (SF), no volatilizer or graduated
dispenser should be used. For phosphine (PH), a chamber is generally
not used because phosphine will corrode copper and brass (including
tubing, fans, and electrical wiring).
Fans or blowers developing the prescribed minimum air movement are
essential to the proper distribution of the fumigant.
Chambers may be equipped with heating or refrigeration units
depending on the climatic environment and the products to be
fumigated. Product injury or an ineffective fumigation may occur
within certain temperature ranges. Although provisions for
temperature control are not generally mandatory, in certain
fumigation operations temperature control is necessary and therefore
must be considered in the design and construction.
While complete construction details for an atmospheric fumigation
chamber are not contained in the following narrative and illustrations,
sufficient information is available to develop specifications for a
proposed structure. Firms considering chambers for approval by the
U.S. Department of Agriculture should submit drawings to the Center
for Plant Health Science & Technology (CPHST) in Religh, North
Carolina.
Basic Elements for Design and Construction of Chambers
◆ Must be gas tight and must remain so during every use.
◆ Must be provided with an efficient system for circulating and
exhausting the fumigant.
◆ Must be provided with an efficient system of dispensing the
fumigant.
◆ Must be provided with suitable fittings to facilitate a
pressure-leakage test and gas concentration sampling.
◆ Should be provided with a recording thermometer when product
temperatures are critical or treatments are of such duration that
temperature variations could affect the efficiency of the
fumigation.
　
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