Abstract:
An apparatus for detecting the presence of powdered materials in envelopes comprises a container with an envelope-positioning unit, envelope corner or edge cutter, a powder excitation and extracting means for shaking the contents of the envelope, and a powder detector with a particle intake device, and air circulation system for circulation of the particle-containing air through the powder detector. The detector can be placed inside or outside of the sealed container and is connected to the cutting zone via the particle suction device. In operation, the envelope is placed into the envelope-positioning unit. Either a corner or an edge of the envelope is cut off or perforated so as to allow a part of the powdered material to leave the envelope while maintaining the other contents, except for small particulates, intact and inside the envelope. The envelope is then subjected to vibration or impacts under the effect of the excitation means. In case of detection of a hazardous material, the apparatus will produce alarm signals and will lock the door to restrict access to the apparatus.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for detecting the presence of powdered materials in closed envelopes, in particular, for detecting powdered infectious, contagious, contaminating, or other undesired substances that can be sent via mail. 
     BACKGROUND OF THE INVENTION 
     Recent increase in the acts of terrorism, in particular, of bio- and chemical terrorism, caused US Government to undertake development of new reliable and rapid-response measures for dealing with the suspicious substances in the mail, which appeared to be one of convenient channel for delivery of contagious bio- and chemical substances to governmental offices, companies, and individuals. One such measure is irradiation of mail started by the U.S. Postal Service in response to anthrax mail contamination that has been found on Capitol Hill, in White House Postal Service, in offices of senators, and in other locations. Contaminated mail has sickened more than a dozen people and claimed the lives of postal workers at some mail sorting centers. 
     PlasmaSol Corp., N.J., has developed “nonthermal plasma” that emits germ-killing ultraviolet rays and creates ozone that oxidizes chemicals and bacteria like a disinfectant. This device can work under normal atmosphere and therefore do s not require the use of complicated and expensive vacuum and vacuum-sealing equipment. Tests on the anthrax-like bacteria have generated positive results. However, regular envelopes are not transparent, and thus high doses of ultraviolet irradiation are required, which limits its practical use. 
     Total irradiation of the entire mail circulating through the United States may be an unreal objective in view of its high cost and extremely small amount of contaminated mail as compared to millions of items circulating daily through the channels of the U.S. Postal Service. High radiation doses needed for decontamination of bacteriological particles require expensive protection of and highly qualified personnel working with this equipment at postal facilities. Also, maintenance of the mail irradiation equipment will be no less expensive than its operation. 
     In view of the sporadic and random distribution of contaminations mail, it would be more appropriate to conduct selective screening at the mail destination locations only of those letters and packages that seem suspicious. However, since the United States were taken with the acts of bio-terrorism by surprise, this country has not yet developed reliable equipment for the solution of the above problem. 
     In fact, some specialized biological agent detection devices existed in the civil defense system. For example, in 1994 the Department of Defense disclosed the existence of almost 40 Biological Integrated Detection Systems (BIDS) designed for Army. However, all these systems were intended for battlefield conditions and had not been introduced into practical use, due to no demand for such use. Nevertheless, at the present time BIDS uses off-the-shelf instrumentation, including an aerosol-particle counter/sizer, a bioluminescence analyzer, a liquid-particle counter/sizer, a particle sampler, and a manual antibody-based detector. Among the agents that BIDS is required to detect and identify are anthrax and plague bacteria, botulinal toxin A, and staphylococcal enterotoxin B. 
     In response to the recent anthrax menace, some commercial companies have developed and are selling on-site detection kits for anthrax, as fears of the often-lethal bacteria spread across the country. One example of such bacteria-detection equipment is Smart Cycler, produced by a private company Cepheid, California. This device combines optical spectroscopy with fluorescent analysis and makes it possible to detect anthrax and other hazardous biological substances. 
     Although the Smart Cycler operates reliably and efficiently, it is only a detection device, which requires a special procedure for preparation of test samples. Furthermore, this device, like any other detector, requires preliminary revealing of suspicious objects, e.g., closed postal envelopes with suspicious contents. It is well known that in majority of cases the biological contaminants comprise fine powders, which are convenient for delivery through mail and which immediately scatter in air when the envelope is opened. Thus, prior to detecting and defining the suspicious powder, it is necessary to reveal a suspicious envelope, to open it under conditions safe for the personnel, and to test the interior of the envelope for the presence of a powder, irrespective of whether this powder is contagious or neutral, and only in the case the powder is found, it is then detected and analyzed in such a device as Smart Cycler. However, at the present time none such equipment, suitable for use in facilities receiving from several to thousands letters per day, is available. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a method and apparatus for revealing mail with suspicious contents as a measure of preliminary presorting of closed postal envelopes and for making the mail with suspicious substances available for a further detailed analysis. It is another object to provide the aforementioned apparatus, which is simple in construction, inexpensive to manufacture, simple and safe in use, and incorporates a commercially produced particle detector. It is another object of the invention to provide the aforementioned apparatus, which is equipped with an electronic control unit that controls operation of a cutter, envelope excitation means, alarm and locking devices. It is another object to provide the aforementioned apparatus and method suitable for use in mailrooms of enterprises, companies and establishments that daily receive from several to thousands items of mail. 
     An apparatus of the invention for detecting the presence of powdered materials in closed envelopes comprises a sealed container provided with a loading/unloading port, an envelope-positioning unit, envelope corner or edge cutter, a powder excitation and extraction unit for exciting the contents of the envelope, and a powder detector with a particle intake device, and an air circulation system for circulation of the particle-containing air through the powder detector. The detector can be placed inside or outside of the sealed container and is connected to the cutting zone via the particle suction device. In operation, each piece of the selected suspicious mail is placed into the envelope-positioning unit that can be located inside the container, e.g., on the backside of the door, so that either a corner or an edge of the envelope is aligned with the position of the cutter. The door is closed for sealing the container with the envelope to be tested. The corner or the narrow edge of the envelope is cut off or perforated so as to allow the powdered material to come out from the envelope while maintaining the other contents, except for small particulates, intact and inside the envelope. The envelope is then subjected to either vibrations or impacts under the effect of the excitation and extraction device. If the envelope contains any fine powdered material, the vibrations will excite the fine powdered particles, which begin to move. This will cause the powder to leave the envelope through the opening formed in the cut-off corner or edge perforations of the envelope. The particles suspended in air underneath the envelope corner will be sucked into the particle intake device and delivered to the powder detector. The results of particle analysis can be displayed or recorded, as well as analyzed by a control unit, while the air exhausted from the powder detector will return to the container and will circulate through the above-described path. The judgment on the presence of the suspicious substance will be made by comparing the measured data with a predetermined reference threshold. The maximum threshold value for the number of particles unloaded from a single envelope is selected based on real conditions, according to which the detector will produce an alarm signal if the number of particles will exceed the predetermined threshold. In case of detection of a hazardous material, the apparatus will produce both sound and visible alarm signals, at the same time locking the door to prevent access to the apparatus for unauthorized personnel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front vertical sectional view of the apparatus of the invention. 
     FIG. 2 is a sectional view along the line II—II of FIG. 1 illustrating position of the powder excitation and envelope material remover devices. 
     FIG. 3 is a schematic view of the embodiment of the apparatus of the invention with an electromagnetically driven envelope material remover and a loudspeaker-type powder excitation and extraction unit. 
     FIG. 4 illustrates an embodiment of the apparatus of the invention with an impact-type powder excitation device. 
     FIG. 5 illustrates a simplified embodiment of the invention, in which the envelopes are handled manually inside the sealed transparent container with the use of latex gloves. 
     FIG. 6 is a view of a modified envelope material remover for perforating a narrow edge of the envelope. 
     FIG. 7 is a fragmental view of the device of FIG. 6 with the perforated envelope. 
     FIG. 8 in is a three-dimensional front view of the apparatus of the embodiment. 
     FIG. 9 is a top sectional view of the apparatus of FIG. 8 in the direction of arrows IX—IX. 
     FIG. 10 is a side sectional view of the apparatus of FIG. 8 in the direction of arrows X—X. 
     FIG. 11 is a sectional view of the parts and units on the inner side of the door in the direction of arrow XI—XI in FIG.  9 . 
     FIG. 12 is a schematic view of the envelope material remover used in the apparatus of FIGS. 8-11. 
     FIG. 13 is a fragmental view of the envelope cutting and powder suction zone of the apparatus of FIGS. 8-12. 
     FIG. 14 is an electrical block diagram of the apparatus of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An apparatus made in accordance with one embodiment of the invention is shown in FIGS. 1 and 2. Here FIG. 1 is a front vertical sectional view of the apparatus of the invention. FIG. 2 is a sectional view along the line II—II of FIG. 1, illustrating position of the particle excitation and extraction unit and the cutter. 
     In the context of the present invention, the term “powdered material” covers any substance in the form of coarse, fine, or very fine particles from millimeters to nanometers. This term covers powders and powder-like materials, e.g., in the form of thin short fibers, or the like. 
     In the context of the present invention the term “envelope” covers various pieces of mail or delivery including letter, parcels, etc. In the context of the present invention, the term “closed envelope” means that the envelope protects its contents from unauthorized observation, even though the corner or the edge of the envelope is cut off or perforated. 
     As can be seen from FIGS. 1 and 2, the apparatus, which in general is designated by reference numeral  20 , consists of a container  22  having a cover  24  located at the top of the container  22  and capable of closing the container  22  so that the interior of the container is sealed by a seal element  26 . As can be seen from FIG. 2, the rear wall  28  is inclined with respect to a vertical front wall  30  and vertical side walls  32  and  34  of the container. All the walls of the container should maintain the interior of the container tightly sealed when the cover  24  is closed. On its front side, the inclined rear wall  28  of the container  22  supports an envelope-positioning unit  36 . As can be seen from FIGS. 1 and 2, the envelope-positioning unit  36  is made in the form of a trough composed of two inclined plates  38  and  40 , which are substantially perpendicular to the rear wall  28  and to each other. However, as can be seen from FIG. 1, the converging ends of the inclined plates  38  and  40  do not intersect in an apex point but rather are discontinued at some distance from the apex so that a space is left for protrusion of the envelope corner when the envelope E is inserted into the envelope-positioning unit  36 , as shown in FIG.  1 . Reference numeral  42  designates a spring-like clamp for securing the envelope E inside the envelope-positioning unit  36 . 
     The rear wall  28  is made of a resilient material, such as a spring-type stainless steel so that this wall could function as a resilient membrane. On its backside (FIG.  2 ), the rear wall supports an excitation and extraction unit  44 , e.g., in the form of an acoustic loudspeaker, so that the acoustic waves generated by the loudspeaker  44  will cause the rear wall  28  to vibrate. The powder excitation and extraction unit causes at least a part of the powder material to separate from the envelope and to leave the envelope with an air flow through the opening produced by cutting. The loudspeaker  44  is provided with an either single-pulse or a.c. generator  46  located outside the apparatus  20 , which is connected to the loudspeaker  44  via an amplifier  48 . The loudspeaker  44  is rigidly connected to the backside of the rear wall  28 . The generator  46  may generate either single pulses or alternating current with frequency from several Hz to several kHz. The alternating current can be generated in a continuous, intermittent or programmed mode selected for optimization of conditions required for excitation and extraction of powder that may be contained in the envelope. The amplitude of the oscillations can be controlled via the amplifier  48 . 
     The container  22  may have a transparent window  50 , which in FIG. 2 is shown in the cover  24 , though the window can be formed in any other wall of the container  22 . 
     In the area of the envelope-positioning unit  36  open for protrusion of the envelope end, e.g., corner C (FIG.  1 ), the apparatus  20  is provided with an envelope end remover  52 . In FIG. 2, the remover  52  is schematically shown in the form of a cutter blade  54  provided on the end of the remover and reciprocating in guides  56  fixed in the container. A handle  58  projects outside the container  22  through the front wall  30  of the container. Bellows  60  are used for sealing the interior of the container from the projecting end of the remover  52 . A return spring  62  automatically lifts up the blade  54  from the envelope after the cut is completed. Pushing on the handle  58  starts cutting of the envelope corner. A clump  64  that functions as a support for the corner C of the envelope E during cutting can be provided in the trough against the cutting blade  54 . 
     On its way towards the envelope, the handle  58  engages an excitation switch (not shown) that activates the generator  46 , and thus causes the loudspeaker  44  to vibrate and shake the rear wall  28  of the container  22 . 
     The particle detection system consists of a particle detection unit  66  (FIG.  1 ), sealingly connected to the interior of the container  22  via a particle intake suction pipe  68 , and a return pipe  70  for returning the air from the powder detector back to the interior of the container  22  for recirculation. As can be seen from FIGS. 1 and 2, for convenient entrance of particles, the suction port of the particle intake suction pipe  68 , which is inserted into the interior of the container underneath the area where the corner of the envelope E is to be located, may have a funnel-like shape. A vacuum pump  72  is installed in the particle intake suction pipe  68  for suction of particle-carrying air and for the supply thereof to the powder detector  66 . The particle intake pipe  68  has a replaceable and disposable suction cup  74  that can be easily replaced. In order to facilitate sterilization of the interior of the container  22 , the inner walls of the container  22  should be smooth with rounded corners. 
     Powder detector  66  can be selected from a group consisting of a particle counter counting the number of powder material particles, particle geometry analyzer analyzing the geometry of powder material particles, particle physical analyzer analyzing the physical properties of powder material particles, and particle chemical analyzer analyzing the chemical properties of powder material particles. Examples of commercially available airborne particle detectors suitable for use in conjunction with the apparatus of the invention are devices produced by Japanese company Rion Corporation, models KC20, KC-01D1, and KC-03A1. This device is based on optical scattering, has a suction unit with capacity of 30 liter/min, has an alarm function. It can detect particles of different sizes from 0.3 to 100 microns, in concentration from 0 to 2000 particles/liter. This device and its models are given only as an example. 
     The apparatus of the embodiment shown in FIGS. 1 and 2 operates as follows. 
     It is understood that the apparatus of the invention can be used for checking the entire mail, if volume of the mail allows such treatment, or selectively only for suspicious envelopes. For checking an envelope E (FIG.  1 ), the cover  24  of the container  22  is opened, and the envelope E is placed into the envelope-positioning unit  36  so that the envelope corner C is positioned in the cutting zone of the cutting blade  54 . The cover  24  is then closed so that the interior of the container  22  is sealed from the surrounding environment. The interior of the container  22  is seen through the transparent window  50 . The operator then activates the powder detector  66  so that the suction pump begins to suck air from the interior of the container  22  and to supply it to the powder detector  66 . The operator pushes on the spring-loaded handle  58  of the cutter  52  whereby the cutter blade  54  cuts off the envelope corner C. Pushing on the handle  58  closes the contacts of the above-described excitation switch, whereby the envelope excitation device  44  is activated. If necessary, prior to operation, the generator  46  can be adjusted with regard to the frequency of pulsing impacts or oscillations in order to select the optimal mode for the types of envelopes checked in the apparatus of the invention. 
     If the envelope E contains a powdered material, under the effect of excitation transmitted from the loudspeaker  44  to the rear wall  28  of the container that supports the envelope-positioning unit  36 , the powdered material will pour out from the envelope E through the opening in the envelope corner C. As a result of a suction force developed at the funnel-shaped intake suction pipe  68  by the action of the vacuum pump  72  of the powder detector  44 , the powdered material will be sucked into the pipe  68  and delivered to the powder detector  44 . Not only those particles of the powder that fall directly into the suction pipe enter the powder detector, but also airborne fine particles that are suspended in the space within the container will be drawn into the intake pipe  68  and hence into the powder detector  44 . 
     Modern particle detectors, such as some of those produced by Rion Corporation and shown herein as an example of a detector suitable for the apparatus of the present embodiment, are capable of determining not only the number of particles received by the detector and counted in a unit volume of the sucked air, but also the dimensions of the particles and distribution over the dimensions. Data relating to the size and dimensional distribution of the particles in some cases can be used for determining the material of the powder, provided the powdered substance has very specific dimensions of particles and dimension dispersion. The dimension dispersion curves may be used for preliminary identification of the substance found in the envelope. More reliable detection of the powered materials can be conducted under laboratory conditions with the use of instruments such as the aforementioned Smart Cycler produced by a US company Cepheid, California. 
     The apparatus of the invention may be equipped with a mechanically driven envelope material remover. In the context of the present invention, “envelope material remover” is a general term that covers devices for separating a part of the envelope material from at least one envelope corner or at least one envelope edge in order to form an opening for extraction of powder materials from the inside the envelope. The envelope material remover can be a cutter, a punching or perforating device or the like. 
     For example as shown in FIG. 3, the blade  54  can be driven electromagnetically with a solenoid core  58   a  which can be made from a magnetic material such as iron. The solenoid  76  can be activated by pushing on a push button or pedal  78  (FIG.  3 ). The cutter drive mechanism shown in FIG. 3 consists of a pushing rod  82  which is connected to the core  58   a  and guided in guide  84 . The apparatus of the embodiment equipped with the electromagnetically driven cutter operates in the same manner as the apparatus with the manually driven cutter shown in FIGS. 1 and 2, with the exception that the cutter will be activated by pushing/pressing on the button/pedal  78 . 
     FIG. 4 illustrates another embodiment of the apparatus of the invention, in which a powder excitation and extraction unit  44 , shown in FIGS. 2 and 3, is replaced by an impact-type excitation device  86 . The excitation device  86  includes a plunger  88  driven with an electromagnetic coil  90 . This coil interacts with the rear end of the plunger, which functions as a core  92  of the solenoid. When the coil  90  is activated, it pulls the plunger  88  away from the rear wall  94  and extends the spring  96 . When the contacts  98  of the electromagnetic coil  90  are de-energized, the spring  96  returns the plunger towards the rear wall  94 , whereby a blow is applied to this wall. The impact of this blow is transmitted to the rear wall  94  and hence to the envelope, whereby the contents of this envelope is shaken. This arrangement can be reversed so that the blow will be applied by the core and the spring will return the core to the initial position. Activation of the electromagnetic excitation device  86  can be interlocked with activation of the electromagnetic cutter  100  so that the corner of the envelope E′ is cut simultaneously with application of impacts. 
     FIG. 5 illustrates a simplified embodiment of the invention, in which the envelopes are handled manually inside the sealed transparent container  102  by means of latex gloves  104   a  and  104   b  inserted into the container  102  through sealing sleeves  106   a  and  106   b . The gloves  104   a  and  104   b  can be inserted through the front or side walls of the container  102 . The operator may use the gloves for manually positioning the envelope E″ in the envelope-positioning unit  108 , while the cutter  110  can be activated by pushing on buttons  112   a  and  112   b . The two buttons are used in order to cause the operator to use both hands for activation of the envelope material remover. This is necessary for safety reasons in order to protect the operator&#39;s hands from the cutting action of the blade. Reference numeral  166  designates a powder detector. 
     FIGS. 6 and 7 show a modified shape of the envelope material remover  114  suitable for all previously described embodiments. In the embodiment of FIG. 6 the envelope material remover either cuts off or perforates or punches at least a part of at least one edge of the envelope. More specifically, the envelope material remover  114  has an intermittent cutting edge in the form of a plurality of cutting rods or punches  114   a ,  114   b , . . .  114   n , that may have, e.g., a circular cross section. The rods  114   a ,  114   b , . . .  114   n  may have cutting edges similar to those in conventional paper punches. The envelope E 1  is positioned in the envelope-positioning unit  116 , which is inclined to the vertical similar the previous embodiments, so that the projection of the rods  114   a ,  114   b , . . .  114   n  onto the envelope overlap only a portion of the narrow envelope edge  118 . The surface of the plate  119  (FIG.  7 ), which supports the envelope E 1  in the envelope-positioning unit  116 , has holes aligned with the positions of the rods so that during the cutting cycle, the punching rods will cut or punch only portions of the envelope edge  118  in a discrete manner so that after cutting the envelope will look as shown in FIG. 7 with a plurality of uncut portions  122   a ,  122   b , . . .  122   n . These uncut portions will preserve the confidentiality of the mail. The perforated portions  124   a ,  124   b , . . .  124   n  formed in the envelope will allow the powder to come out from the envelope. This embodiment with the modified envelope material remover can be used in conjunction with the drives of the envelope material remover shown in any previous embodiment. In the embodiment of FIGS. 6 and 7 at least one edge  121  of the cut side of the envelope should be used for supporting and for positioning of the envelope with respect to the envelope material remover, while the remaining part  123  of the envelope side will be punched. 
     Another embodiment of the invention is shown in FIG. 8, which is a three-dimensional front view of the apparatus. The apparatus, which in general is designated by reference numeral  200 , consists of a hollow rectangular container  202 , the front side of which can be opened or closed by means of a door  204 . Located beneath the container  202  is an electronic unit  203  which may be placed into a separate lower compartment of the container  202  or into a separate housing that may support the container  202 . Other parts and elements seen on FIG. 8 are a door handle  208 , a start button  210 , an alarm indicator lamp (red)  212 , and a normal operation status indicator lamp (green)  214 . The start button  210  and indicator lamps can be located on the door  204  or on the top of the container  202 . Reference numeral  242  designates an ON/OFF switch for electronics located on the electronics unit;  215  is a power supply cord. 
     FIGS. 9,  10 , and  11  illustrate arrangement and mutual positions of parts and units inside the container  202 . FIG. 9 is a top sectional view of the apparatus of FIG. 8 along the line IX—IX of FIG. 8, FIG. 10 is a side sectional view of the apparatus of FIG. 8 in the direction of lines X—X of FIG. 8, and FIG. 11 is view of the parts and units on the inner side of the door in the direction of line XI—XI in FIG.  9 . 
     As shown in FIG. 10, the apparatus is provided with a door lock  206 . The door lock  206  is provided with a solenoid  211 , the core of which is located under the backside of the lock  206 . Each time the door is closed, the solenoid  211  is activated, its core is raised and the door  204  is locked. In order to open the door  204 , the operator pushes on a door-opening button  217  (FIG.  8 ). In the case the apparatus has detected a hazardous material, the solenoid  211  is deactivated, so that its core remains in raised up position and locks the door  204 . This prevents the door of the apparatus from opening by a non-authorized person. For unlocking the door  204 , the apparatus is provided with a key reset socket  213  located on the electronics compartment (FIG. 8) for a key reset switch  209  (shown in FIG. 8) accessible only to an authorized personnel. 
     As can be seen from FIGS. 10,  11 , the inner side  205  (FIG. 11) of the door  204  supports an envelope-positioning unit  216  that consists of two mutually perpendicular slotted guide plates  218  and  220  which do not intersect and leave in an imaginary point of intersection a space  222  for positioning of the envelope corner. For convenience of insertion of the envelopes, the guide plates  218  and  220  may be inclined with respect to the vertical direction. 
     Located directly above the space  222 , i.e., above the corner of the envelope E 2  shown in FIG. 11 in the working position inside the envelope-positioning unit  216 , is a guillotine-type envelope material remover  224 , which is also attached to the inner side  205  of the door  204 . A schematic view of the envelope material remover  224  is shown in FIG.  12 . In this embodiment, the envelope material remover  224  consists of a moveable blade  226  and a stationary blade  228 . The moveable blade  226  slides in two parallel guides  231  and  233  and is rigidly attached to one end of an L-shaped bracket  234 , the other end of which is rigidly connected to an actuating mechanism, such as a pull-type solenoid  236 . The bracket  234  is connected to a return spring  235  that normally maintains the moveable blade in the raised position. Activation of the solenoid  236  by pushing on the start button  210  (FIG. 8) will pull the solenoid core and hence the moveable blade  226  in the direction of the stationary blade  228 . The path of the moveable blade  226  passes through the space  222  and hence through the corner of the envelope E 2  (FIG. 11) placed into the envelope-positioning unit  216 , whereby the corner of the envelope E 2  is cut off. 
     As shown in FIG. 10, the apparatus  200  is provided with a powder detector  230 , which in this embodiment is located inside the apparatus. Powder particles detection and evaluation means can include one or several of the following devices: particle counter counting the number of powder material particles, particle geometry analyzer analyzing the geometry of powder material particles, particle physical analyzer analyzing the physical properties of powder material particles, and particle chemical analyzer analyzing the chemical properties of powder material particles. For example, the powder detector  230  may be a standard portable particle counter, e.g., GT-321 type produced by Met One Instruments, Inc., Oregon, US. This small self-contained device is suitable for monitoring particle sizes from 0.3 microns to 5 microns in concentrations from 0 to 3,000,000 particles per cubic foot. It works on rechargeable batteries and incorporates a suction system. 
     The intake or suction tube  232  (FIG. 9) of the detector  230  has on its end a funnel-shaped suction cup  237  that is located directly under the cutting zone  222  (FIG.  11 ). The surface of the suction cup is coated with a thin filter for passing the powder and for preventing penetration of envelope cut-off debris into the detector. 
     FIG. 13 is a fragmental view of the envelope cutting and powder suction zone of the apparatus  200 . As shown in FIGS. 11 and 13, the apparatus is provided with a debris collection tray  239  located directly under the cutter  224  and under the space  222  so that the debris, such as the cut off corner of the envelope E 2 , will fall into the debris collection tray  239 . In order to direct the cut-off corner away from the suction cup  237  and into the tray  239 , a guide plate  238  of the type shown in FIG. 13 is attached to the back side of the moveable blade so that when the moveable blade  225  approaches the cutting position, the guide plate also enters the space under the cutting zone for directing the debris to the tray  239 . 
     An powder excitation and extraction unit  240  (FIGS. 9,  10 , and  11 ) used in the apparatus of the embodiment is the same as the shaker  44  of the previous embodiment shown in FIGS. 2 and 3. The unit  240  is made in the form of an acoustic loudspeaker installed on a vertical compartment wall  241  (FIGS. 9 and 10) installed inside the container  202 , so that the front vibrating surface of the loudspeaker that generates acoustic waves is located in close proximity to the envelope E 2  placed into the envelope-positioning unit  216 . The loudspeaker  240  is provided with an a.c. generator connected to the loudspeaker via an amplifier. The a.c. generator and the amplifier of this embodiment are not shown in the drawings and are located in the electronics compartment  203  (FIG.  8 ). 
     FIG. 14 is a block diagram of the control system of the apparatus of the invention. Through a general ON/OFF switch  242  the power supply unit  244  is connected to a conventional a.c. power network that supplies current to the cutter solenoid  236 , the loudspeaker  240 , and to the powder detector  230  via an AC/DC adapter  246  (electrical connections are not shown in FIG.  14 ). The powder detector  230  may operate from an accumulator battery as well. Control of the apparatus is carried out from a control unit  248  located inside the electronics compartment  203  (FIG.  8 ). More specifically, the control unit  248  controls operations of the alarm indicator lamp (red)  212 , the normal operation status indicator lamp (green)  214 , a warning sound speaker  249 , the loudspeaker  240 , the cutter solenoid  236 , and the door lock solenoid  211 . The apparatus is activated by pushing on a start button  210 . 
     Reference numeral  250  designates a safety limit switch, which allows operation of the apparatus of the invention only when the container door is sealingly closed. 
     Operation of the Apparatus of the Invention 
     Either all incoming mail or only envelopes that may contain a suspicious substance are selected for checking in the apparatus of the invention. In the case of the embodiment described with reference to FIGS. 1-4, the operator opens the cover  24  located at the top of the container  22 , and manually places a selected envelope into the envelope-positioning unit  36  so that the corner C of the envelope protrudes into the path of movement of the cutting blade  54  (FIG.  3 ). The operator then closes the cover  24  so that the interior of the container is sealed with a seal  26 . The operator activates the solenoid  76  or  100  by pushing/pressing on the push button/pedal  78  (FIG.  3 ). The push button and pedal are also interlocked with activation of the excitation and extraction unit, so that the corner of the envelope is cut off, and at the same time the envelope is shaken with either the loudspeaker  44  (FIG. 3) or the plunger  88  (FIG.  4 ). The powder excitation and extraction unit  44  causes at least a part of the powder material to separate from the envelope and to leave the envelope with an air flow through the opening produced by cutting. 
     If the envelope contains a powdered material, this material will be sucked under the effect of the vacuum pump  72  into the powder detector  66  via the suction cup  74  and the supply tube  68 . Depending on the type of the powder detector  66 , the particles of the powder can be merely counted or analyzed, and the results of the analysis or count are compared with a predetermined value. In case the number of particles exceeds the preselected value or the results of analysis coincides with the preselected reference value, the apparatus generates an alarm signal warning the operator about the event of detection. If necessary, in this case the entire apparatus can be transported to another location for further analysis of the detected material and for appropriate treatment. 
     In the embodiment of FIG. 5, the cover is opened, the operator manually positions the envelope E in the envelope-positioning unit  108 , the cover is closed, and the container is sealed. The operator then inserts the hands into the gloves  104   a  and  104   b  for repositioning of the envelope, if necessary, and pushes on two buttons  112   a  and  112   b  simultaneously (as a safety measure) for activation of the an envelope material removal device selected from a group consisting from cutting, punching, perforating, puncturing and tearing devices (not shown in FIG.  5 ). Pushing only on one button will not activate the envelope material removal device. 
     The device of the embodiment shown in FIGS. 6 and 7 may incorporate all the features of the previous embodiments and therefore operates in the same manner as described above. The only difference is that the envelope material removal device  114  consists of a plurality of cutting or punching rods  114   a ,  114   b , . . .  114   n  and that the envelope is positioned in the envelope-positioning unit  116  so that a narrow edge of the envelope E 1  projects into the path of the cutter. As a result, after activation of the envelope material removal device  114 , the latter discretely perforates the edge of the envelope. The edge perforated as shown in FIG. 7 allows the powder to leave the envelope while the rest of the contents of the envelope remains inside the envelope. 
     Referring now to the embodiment shown in FIGS. 8-14, it should be noted that many features shown and described in connection with this embodiment, such as electronics compartment, safety lock of the door, a keylock feature, etc., could be incorporated into the embodiments of FIGS. 1-7 as well. Therefore, it should be assumed that description of operation of these features in connection with the embodiment of FIGS. 8-14 should be associated also with the embodiments of FIGS. 1-7. 
     The operator opens the door  204  located at the front side of the container  202  by pushing on the door-opening button  217 . This action activates the solenoid  211  (FIG.  10 ), the core of this solenoid is pulled into the coil and releases the lock  206  for opening the door. The operator manually places a selected envelope E 2  (FIGS. 11 and 13) into the envelope-positioning unit  216  so that the corner R of the envelope E 2  protrudes into the path of movement of the moveable blade  226 . The operator then closes the door  204  so that the interior of the container is sealed. By pushing on the start button  210 , the operator initiates a sequence of operations consisting in activation of the solenoid  236  of the envelope material removal device (FIG.  12 ), cutting the protruding corner R of the envelope (FIG.  13 ), and activating the loudspeaker  240  (FIGS.  10  and  14 ). Pushing on the start button  210  also activates the powder detector  230  located inside the container (FIGS.  9  and  10 ). 
     As the moveable blade  226  moves down while performing its cutting stroke, it lowers the debris guiding plate  238  into a position in which it directs the cut-off corner of the envelope to the tray  239  (FIG.  13 ). 
     If the envelope E 2  contains a powdered material, this material will be sucked into the powder suction cup  237  (FIG. 13) located near the cutting zone. Depending on the type of the powder detector  230 , the particles of the powder can be merely counted or analyzed, and the results of the analysis or count are compared with a predetermined value. In case the number of particles exceeds the preselected value or the results of analysis coincides with the preselected reference value, the apparatus generates an alarm signal warning the operator about the event of detection. More specifically, the control unit  248  stores predetermined data corresponding to different types of powdered materials, compares the results of measurements with this data, and generates comparison data used for judgment on the presence or absence of the powdered material. 
     The alarm signal, which is generated in response to the aforementioned comparison data, deactivates the solenoid  211 , and this action blocks the lock  206  thus preventing the door  204  from opening by non-authorized personnel. In this case the door  204  can be opened only by an authorized person with the use of a special reset key  209  (FIG.  8 ). If necessary, in this case the entire apparatus can be easily transported to another location for further analysis of the detected material and for appropriate treatment. 
     Thus it has been shown that the invention provides a method and apparatus for revealing mail with suspicious contents as a measure of preliminary presorting of closed postal envelopes and for making the mail with a suspicious substance available for a further detailed analysis. The invention provides an apparatus simple in construction, inexpensive to manufacture, simple and safe in use, and incorporating a commercially produced particle detector. The invention also provides the aforementioned apparatus and method suitable for use in mailrooms of enterprises and companies that daily receive from several to thousands items of mail. 
     Although the invention has been shown and described with reference to specific embodiments, it is understood that these embodiments should not be construed as limiting the areas of application of the invention and that any changes and modifications are possible, provided these changes and modifications do not depart from the scope of the attached patent claims. For example, powder detectors of the types different from those shown and described in the specification may be suitable for use in conjunction with the apparatus and method of the invention. The cover of the container may have a slot located above the envelope-positioning unit for dropping the envelopes into the converging guides of the aforementioned envelope-positioning unit for self-orientation. The display of the powder detector may be located in a place remote from the apparatus. The powder detector can be provided with various adjustable alarm systems responding to the type of powder found in the envelopes. The powder excitation and extraction units may be of the types different from those shown and described and provided with means for adjusting the mode of operation to match with the types of the envelopes processed in the apparatus of the invention. It is understood that the cutter for perforation of the envelope edge can also be used in conjunction with operating units of the embodiment of FIGS. 8-14. The envelope material removal device may be different from the guillotine type and include punching, perforating, puncturing or tearing components, removal of the envelope material by etching, laser treatment, etc. The safety lock mechanism can be installed on the container cover as well.