Abstract:
A method for collectively sampling a plurality of cargo items for contaminants such as chemical residues. The items are placed in a generally airtight chamber and agitated physically to release particulates and vapors from the surfaces and interior of the items. The methods of physical agitation include vibrating the items, and pressurizing and depressurizing the chamber, with the pressurizing being done by introducing bursts of high pressure air into the chamber and by directing jets of high pressure air at the cargo. Optionally, the high pressure air may be heated or mixed with solvent vapors. This physical agitation drives particulates and vapors of contaminants into suspension in the air in the chamber. Air withdrawn during depressurization is passed through a collection system to collect the particulates and vapors for subsequent analysis.

Description:
This application is a continuation-in-part of International Application No. PCT/US98/11805, filed Jun. 9, 1998, which is a continuation of U.S. Application Ser. No. 08/873,394, filed Jun. 12, 1997, now U.S. Pat. No. 5,942,699, issued Aug. 24, 1999. 
    
    
     FIELD AND BACKGROUND OF THE INVENTION 
     The present invention relates to a method and apparatus for sampling cargo for chemical residues and, more particularly, to a method and apparatus for extracting particulates and vapors of chemical residues simultaneously from multiple cargo items. 
     Cargo, such as agricultural produce, general merchandise, and passengers&#39; baggage, is routinely checked for chemical residues at transit points such as airports, seaports and border crossings generally. In the case of agricultural produce, the residues sought generally are pesticides and other health hazards. In the case of general merchandise and baggage, the residues sought include illicit substances such as drugs and explosives. This sampling can be tedious and time-consuming. For example, agricultural produce is inspected by selecting a representative sample, mechanically chopping the sample and chemically analyzing the sample. The familiar x-ray inspection of passengers&#39; baggage at airports is performed one item at a time. The quality of this inspection depends on the alertness of the operator to spot suspicious items by their outline against complex backgrounds, as well as on equipment limitations. For a more intensive search based on chemical analysis, chemical samples are collected manually from the outside surfaces, or less commonly from the surfaces of the inside contents, of suspect baggage and parcels and transferred to an analytical instrument or to a reagent chemical test kit for identification. These manual sampling/analysis procedures can detect traces of pesticides on or within agricultural produce, as well as traces of illegal drugs and explosives deposited on the sampled surfaces in the course of handling drugs and explosives and hiding them in the baggage, parcels or cargo, but these procedures generally are slow and tedious, and therefore are restricted to a limited random sample of the inspected items. 
     A variety of automatic and semiautomatic systems have been proposed for collecting vapors and particulates from cargo items. These generally require that the items be loaded individually into a sampling chamber, although Cohen et al., in U.S. Pat. No. 5,162,652, teach the simultaneous loading of several items into several chambers, albeit still only one item per chamber. The invention of Cohen et al. and also the inventions of Jenkins, described in U.S. Pat. No. 3,941,357, and of Bradshaw et al., described in U.S. Pat. No. 3,998,101, are directed towards extracting vapor from the interior of sealed cargo by varying the pressure within the sampling chamber, typically by up to about 10% on either side of atmospheric pressure. Corrigan et al., in U.S. Pat. No. 5,345,809, and Reid et al., in U.S. Pat. No. 4,580,440, address the problem of sampling particulates on the surfaces of cargo items. Corrigan et al. teach a sampling chamber in which brushes remove particulates from the surfaces of cargo items. Reid et al. teach the agitation of a cargo transport container to suspend, in the air therein, particulates from the surfaces of the cargo items therein, followed by the sampling of the air with the suspended particulates. None of these prior art patents has addressed the problem of sampling particulates contained inside the cargo items. 
     There is thus a widely recognized need for, and it would be highly advantageous to have, an automatic contaminant sampling method that extracts samples automatically from several inspected items such as cargo items at once, and also extracts particulate contaminants from the interiors of the inspected items. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a method for sampling surfaces and interiors of a plurality of items for contaminant particulates and contaminant vapors, including the steps of: (a) sealing the items inside a chamber containing air at a certain pressure; (b) agitating the items, thereby releasing the particulates and the vapors from the surfaces and the interiors of the items into the air; and (c) inducing a flow of the air, together with the released particulates and vapors, towards a collection system. 
     According to the present invention there is provided a method for sampling surfaces and interiors of a plurality of items for contaminant particulates and contaminant vapors of chemical residues, including the steps of: (a) sealing the items inside a chamber; (b) introducing a gas into the chamber at a certain pressure; (c) agitating the items, thereby releasing the particulates and the vapors from the surfaces and the interiors of the items into the gas; and (d) inducing a flow of the gas, together with the released particles and vapors, towards a collection system. 
     According to the present invention there is provided an apparatus for sampling cargo for particulates and vapors of chemical residues, including: (a) a chamber, enclosing a gas at a certain pressure, wherein the cargo is placed for sampling; (b) a mechanism for agitating the cargo, thereby releasing the particulates and vapors into the gas; (c) a collection system for removing the particulates and vapors from the gas; and (d) a mechanism for inducing a flow of the gas, together with the particulates and vapors, towards the collection system. 
     According to the present invention, cargo items on a pallet are loaded en masse into an airtight chamber and subjected to physical agitation, including vibration, blasts of pressurized air into the chamber, jets of pressurized air directed at the cargo, and cycles of pressurization and depressurization, to release both vapors and particulates from both the interiors and the outer surfaces of the cargo items. The pressurized air may be heated before being directed at the cargo items. Solvent vapors may be introduced to the pressurized air, before it is directed at the cargo items. The adsorption of solvents on the surfaces of particulates often decreases the attractive forces between particulates adsorbed on surfaces and the surfaces on which they are adsorbed, making the particulates easier to dislodge. In addition, most solvents have a higher molecular mass than the constituents of air. Adding these solvents to the air increases the average momentum transfer in a collision between the air and the surfaces on which the particles are adsorbed. Typical solvents used for this purpose include carbon dioxide, acetone, dimethyl sulfoxide, propanol and organic amides. The object of this physical agitation is to knock loose aerosol-size contaminant particles on the exterior and interior surfaces of the items, and to encourage the vaporization of low vapor pressure chemical residues into the air in the chamber. In this manner, contaminant particulates from the outer surfaces of the items and from the interiors of the items are placed in suspension in the air in the chamber, and contaminant vapors from the outer surfaces of the items and from the interiors of the items are mixed with the air in the chamber. During the depressurization phases, air withdrawn from the chamber is passed through a collection system to collect the vapors and particulates. The collected vapors and particulates then are transferred to conventional analytic instruments for identification. If a targeted substance such as a pesticide residue, a trace of an explosive, or a trace of an illegal drug, is identified during this analysis, appropriate steps may be taken, including generating an audible and visible alarm. In addition, the items that were sampled collectively now may be sampled individually, using one or more of the prior art methods, to identify the item bearing the source of the targeted substance. In an airport setting, where the overwhelming majority of the baggage items do not contain contraband, the present invention may be used for an efficient mass preliminary screening of baggage items which is much faster than the prior art methods that deal with one baggage item at a time. 
     To keep the particulates in suspension during the depressurization phases, it has been found necessary to continue the blasts of pressurized air into the chamber during the depressurization phase. These blasts are directed towards the collection system, thereby supplementing the suction that effects the depressurization in inducing a flow of air that entrains the particulates and transports them to the collection system. There are prior art systems, such as those taught by Corrigan et al. in the U.S. Pat. No. 5,345,809 cited above, and by Ellson in U.S. Pat. No. 4,202,200, in which continuously flowing air is used to collect vapors and particulates from people transiting a walk-through sampling chamber and transport the vapors and particulates to a collection system, but there are no prior art systems in which intermittent blasts of air is used to direct the flow of suspended particulates towards a collection system. 
     At the end of a session of physical agitation, the pallet bearing the cargo items is removed from the chamber, and another pallet-load of cargo items is placed in the chamber for sampling. In this way, the cargo is sampled nondestructively and collectively, allowing the cargo to be sampled for contaminants much more quickly and thoroughly than by the present art methods. 
     In one aspect of the present invention, the air in the chamber is replaced with a carrier gas such as carbon dioxide. The cargo then is subjected to physical agitation as described above, with the carrier gas being substituted for air. In other words, the cargo is subjected to pressurized blasts and jets of carrier gas, and the pressure of the carrier gas within the chamber is cycled up and down, with carrier gas containing chemical residue vapors and suspended particulates being withdrawn for collection during the depressurization phases. 
     Although the present invention is directed primarily towards the collection of chemical residues, such as traces of explosives, drugs and pesticides, in the form of particulates and vapors, the scope of the present invention includes the collection of contaminants in general, including particulate contaminants not commonly considered “chemical” residues, such as bacteria and viruses. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: 
     FIG. 1 is a schematic axial cross section through a sampling chamber of the present invention; 
     FIG. 2 is a schematic transverse cross section through the sampling chamber of FIG. 1; 
     FIG. 3 is a partial schematic cross section of a collection system. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is of a method and apparatus which can be used to sample a plurality of cargo items collectively for contaminants. Specifically, the present invention can be used to sample both the surfaces and the exteriors of cargo items for contaminants in the forms of particulates and vapors collectively, nondestructively, and rapidly. 
     The principles and operation of contaminant sampling according to the present invention may be better understood with reference to the drawings and the accompanying description. 
     Referring now to the drawings, FIG. 1 is a schematic axial cross section through a sampling chamber  10  of the present invention, and FIG. 2 is a schematic transverse cross section through chamber  10 . Within chamber  10  is a table  20  mounted on springs  22 . Below table  20  is a mechanism for oscillating table  20 . The specific illustrative mechanism shown here includes a vertical partition  24 , rigidly attached to the bottom of table  20 , to which are attached two contrarotating unbalanced motors  26 . One example of an unbalanced motor  26  that is suitable for this application is the I. F. E. Model G75T, manufactured by Industrie Einrichtungen Fertigungs of Weindhofen an der Ybbs, Austria. Leading into chamber  10  from the top and one side thereof, respectively, are pressure conduits  40  and  40 ′ for conducting pressurized air into chamber  10 . The air in conduits  40  and  40 ′ is pressurized by a compressor  48 . Conduits  40  and  40 ′ are terminated by valves  42  and  42 ′. Conduit  40  branches into a pair of conduits  41  that in turn lead through a pair of heaters  44 , wherein the pressurized air conveyed therethrough from compressor  48  may be heated to up to about 250° C., and through a pair of misting devices  46  that introduces vapors of a solvent into the pressurized air conveyed therethrough from compressor  48 . Similarly, conduit  40 ′ leads through a heater  44 ′ that is similar to heaters  44 , and through a misting device  46 ′ that is similar to misting device  46 . Valve  42 ′ opens directly into chamber  10 , so that pressurized air introduced into chamber  10  in bursts, as described below, expands into chamber  10  in substantially hemispherical pressure waves. Valves  42  open into nozzles  43  that forms pressurize air entering chamber  10  therethrough into high pressure jets. Preferably, valves  42  and  42 ′ are fast-acting, with a response time no greater than about 30 milliseconds. 
     On the side of chamber  10  opposite valve  42 ′ is a depressure conduit  54 . A vacuum pump  50  withdraws air from chamber  10  via conduit  54 . Air withdrawn via conduit  54  traverses a collection system  52  that removes vapors and aerosol particles of possible contaminants from the air passing therethrough. Note the positioning of depressure conduit  54  opposite valve  42 ′. This positioning enables the blasts of air from valve  42 ′ to induce a flow of air towards depressure conduit  54  that, in addition to keeping the particulates in suspension, entrains the particulates and transports them to depressure conduit  54 . For simplicity, only one each of conduits  40 ,  40 ′ and  54 , and only two of conduits  41 , are shown in the Figures. Practical sampling chambers  10  preferably include up to 16 of conduits  40 ,  40 ′ or  41 , and up to 8 of conduits  54 . 
     Compressors suitable for use as compressor  48  include the type LF-5S manufactured by Atlas Copco Airpower of Wilrijk, Belgium. Pumps suitable for use as vacuum pump  50  include the type 5MVP manufactured by Ahim Polak of Azor, Israel. Valves suitable for use as valves  42  and  42 ′ include the type CA76T020 3″ valve manufactured by Goyen Controls of Sidney, Australia. 
     Chamber  10  also is provided with two airtight doors  12  and  12 ′ at either end of chamber  10 . Doors  12  and  12 ′ are raised automatically to open chamber  10  and lowered to close and seal chamber  10 . 
     To sample cargo for chemical residues, door  12  is raised if necessary to open chamber  10 , and a pallet  72  bearing cargo items  70  is deposited on table  20  by a loading mechanism such as a forklift  74 . Door  12  is lowered, and door  12 ′ is lowered if necessary, thereby sealing chamber  10 . Cargo items  70  then are subjected to four kinds of physical agitation: 
     A. Motors  26  oscillate table  20 , thereby vibrating cargo items  70 . The preferred range of vibration frequencies is between about 0.5 cycles per second and about 20 cycles per second. 
     B. The air pressure within chamber  10  is cycled between a maximum of about 1.5 atmospheres and a minimum of about 0.5 atmospheres. The pressurization phase of each cycle is effected by pumping air into chamber  10  via conduits  40  and  40 ′. The depressurization phase of each cycle is effected by pumping air out of chamber  10  via conduit  54 . Preferably, the pressure is cycled at a frequency of between about 0.2 cycles per minute and about 2 cycles per minute, so that every pressurization-depressurization cycle lasts between about 30 seconds and about 5 minutes. Note that the placement of conduits  40 ′ and  54  on opposite sides of chamber  10  tends to promote unidirectional air flow through chamber  10 . 
     C. The pressurization of chamber  10  is not gradual, but is effected in jets of high-pressure air from conduits  41  via nozzle  43  that are directed at cargo items  70 , and in bursts of high-pressure air from conduit  40 ′ into chamber  10  generally. The frequency of the jets is between about one jet per second and about 6 jets per second, and is achieved by opening and closing valve  42 ′ between about once per second and about 6 times per second. The frequency of the bursts is between about one burst every 10 seconds and about 5 bursts per second, and is achieved by opening and closing valves  42  between about once every 10 seconds and about 5 times per second. The jets are active only during the pressurization phases. The bursts continue into the depressurization phases, for almost the entire duration of the depressurization phases, to keep the particulates suspended in the air and to help induce a flow of air directed towards conduit  54 . 
     D. The high pressure air introduced to chamber  10  via conduit  40  is heated by heaters  44  and  44 ′ to about 250° C. To shorten the heating time and provide additional convectional circulation, the air already within the chamber also is heated by one or more heaters (not shown) located inside the chamber. 
     The effect of this physical agitation is to drive vapors and particulates from the surfaces and interior of cargo items  70  into suspension in the air in chamber  10 . During the depressurization phases of the pressurization/depressurization cycles, some of this air is drawn through collection system  52 . Any one of a variety of collection systems, including impact concentrators and cyclone concentrators, may be used. FIG. 3 is a partial schematic cross section of one illustrative collection system  52 , an impact concentrator. Air exiting chamber  10  via conduit  54  is accelerated by passing through a constriction  56  and impacts on a removable collection medium  58  to which the particles entrained in the air flow adhere. Preferably, collection medium  58  is a filter, for example fluorocarbon fiber filter paper having a pore size of about 30 microns. Part of the air flow, including vapors, passes through the filter into an exit conduit  60 ′. The rest of the air flow exits collection system  52  via an exit conduit  60  to a cold trap (not shown) where the vapors are collected. Alternatively, or additionally, collection medium  58  may include strips of a material such as polyimide film that adsorbs the vapors. 
     The particulates and vapors collected in collection system  52  are analyzed by commercially available analytical instruments. Devices suitable for performing explosive detection analyses include the “EGIS” high speed gas chromatography and chemical luminescence explosive detection instrument, developed and manufactured by Thermedics Detection Inc. of Woburn Mass. and partially described in their U.S. Pat. No. 5,092,155. 
     The physical agitation described above is continued for between about one minute and about 4 minutes. Then chamber  10  is brought to atmospheric pressure, door  12 ′ is opened and an unloading mechanism such as forklift  74 ′ is used to remove pallet  72  and cargo items  70  thereon from chamber  10 . 
     While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made.