Patent Number: 052260658
Section: description

DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS Disinfection The present invention relates to a device for disinfecting medical materials. By medical materials, we mean medical and veterinary waste as well as medical products. Medical and veterinary wastes are disinfected, or rendered incapable of causing an infection. The present device inactivates microorganisms in medical and veterinary waste so that the waste can no longer cause an infection. The present device can be used to sterilize or completely kill all bacteria and viruses in, medical products. Both disinfection and sterilization are accomplished through heating and applying gamma radiation by device 1 shown in FIGS. 1 and 2. Preliminary to the use of the present invention, medical material arrives at a processing and recycling facility. Preferably, the material is shipped in sealed containers. This means of shipping medical materials is known in the art and has the advantages that medical waste does not infect its handlers and that contamination of medical products in transit is minimized. At the facility the containers are preferably arranged on pallets and shrink-wrapped with plastic. The pallets are then moved into a heating chamber 10 which is capable of delivering heat by any of a variety of methods, such as radio-frequency, infrared and microwaves and electrical and gas radiant heating. A preferred embodiment of this chamber is a tunnel configuration and means, such as a track 2, for moving the material through the tunnel. This arrangement permits the material to be gradually heated as it travels through. The pallets are held in the heat chamber 10 and exposed to the heat source for a sufficient time to raise the temperature of the medical materials to at least approximately 60.degree. C. It will be recognized by those skilled in the art that temperatures as high as 170.degree. C. may be used without adversely affecting the process. Next, the pallets are moved into a shielded gamma irradiation chamber 20. The gamma chamber is insulated to prevent radiation from escaping into the environment. The same type of facility that is in current use for gamma irradiation of medical supplies may be used for this step. For example, a suitable gamma irradiator is Model #RT 4101, available from Radiation Technology, Inc., Rockaway, N.J. In the chamber 20, a core of radioactive matter (preferably cobalt 60) emerges from a liquid bath and emits ionizing radiation that is relatively constant during the period when any sample is being irradiated. For subsequent loads, the time is gradually increased to account for radioactive decay of the cobalt 60. Absorbed radioactivity is measured in rads. The amount to be delivered to medical materials is measured in megarads (Mrads), or millions of rads. Doses may range from as little as about 0.25 Mrads to as high as about 2.5 Mrads or more. It will be recognized by those skilled in the art that higher radiation doses will not adversely affect the process. In one embodiment, the medical materials are moved along a trackway 2, through the heat chamber 10 and the gamma-irradiation chamber 20. In this arrangement, the distance from radiation sources varies but is additive for the journey through each chamber. The total dose of radiation to which the waste is exposed during its dwell time in the chamber is planned to provide sufficient disinfection. With a track arrangement, the entrance and exit of the chambers are open but additional walls are arranged to block the escape of radiation into the surrounding areas. Such chambers are in common use for cobalt 60 sterilization of medical products. Validation Preferably, a medical material disinfecting facility using the present invention is validated to assure the adequacy of the disinfection process. Validation may be performed when each facility is constructed and at intervals during its operation. Validation may consist of placing heat detecting devices such as thermocouples and/or known amounts of particular microorganisms which are resistant to heat and to gamma radiation respectively into a maximally loaded pallet of medical materials. Sufficient heat to raise the temperature of a sterilizer's load to about 60.degree. C. and a gamma radiation dose of about 0.50 Mrads are delivered to the test pallet. If thermocouples are used, they should all record at least the minimum temperature of about 60.degree. C. After the entire disinfection cycle is complete, the microorganism samples are removed from the pallet and cultured (given nutrients and other appropriate conditions for growth) to determine survival. A typical heat-resistant microorganism which may be used in validation is Bacillus stearothermophilus. A typical radiation-resistant microorganism is Bacillus pumilus. If more than 1 in 10,000 of either microorganism survives the timed cycles, the exposure to heat and/or gamma radiation is increased about 5%, or about 200,000 rads, and another pallet is tested. Device for Recycling Another embodiment of the invention consists of starting with medical or veterinary waste that has been pre-sorted int containers of plastic and general medical waste, respectively. High-grade plastics are used in medical products and can be shredded and remolded into a variety of products. This waste is subjected to heat and gamma radiation as described above. Then the containers of disinfected plastic are moved to a "plastics" shredder 30. For example, an electrically powered shredder with pneumatic ram assist and negative pressure canopy reduces medical waste to small particles and is available as Model Dual 1000 E from Shredding Systems, Inc., Wilsonville, Oreg. The negative pressure canopy minimizes particles entering the surrounding air. The containers are opened and the disinfected plastic is placed in the shredder and shredded to particles of about one quarter to one half inch. This disinfected, shredded material is transferred into 55-gallon drums for shipment to re-users of plastic. Likewise, the containers of disinfected general medical waste are moved to the "general medical waste" shredder. After the containers are opened, the general medical waste is placed in the shredder 30 and shredded to particles of about one quarter to one half inch. The disinfected waste is placed in further containers. This waste contains a mixture of paper, plastic, and metal and can be used as fuel. Possible users include cement kilns which operate at temperatures of about 2,500.degree. F. or more, and which would otherwise use high-sulfur coal. Because this general medical waste is low in sulfur, its use as fuel will decrease sulfur-caused acid rain. Another preferred embodiment of this invention has a heat chamber 10 which is a radio-frequency chamber having a tunnel configuration with the following approximate dimensions: 50 feet long, 20 feet wide and 20 feet high. The tunnel is lined with 3 mm-thick copper sheeting. The copper lining and the arrangement of the electrodes inside the tunnel are designed to confine the radio-frequency waves to the tunnel. In the radio-frequency chamber 10, a system of exciter and ground electrodes generate electromagnetic waves in the radio-frequency band. The radio-frequency band is between audio and infrared frequencies and comprises approximately 10 hertz (Hz) to 300 gigahertz (GHz). When the electrode system is supplied with electricity, it launches an electromagnetic wave into the target medical materials. The radio-frequency waves penetrate the pallets of medical materials. The medical materials absorb these waves whose energy is thought to produce heat by inducing dipole rotation and molecular vibration. When radio-frequency waves are absorbed, they may cause differential heating. Moist articles and metal objects absorb more waves and may create "hot spots," or uneven heating. In closed containers or boxes, the steam and heat from these objects are redistributed to the entire contents of the containers. The pallets are held in the radio-frequency chamber 10 and exposed to radio-frequency waves for a sufficient time to raise the temperature of the medical materials to at least approximately 60.degree. C. It will be recognized by those skilled in the art that temperatures as high as 170.degree. C. will not adversely affect the process. Preferably, the exposure to radio-frequency waves would last about 5 to 30 minutes. More preferably, the medical materials are exposed to the radio-frequency waves for approximately 12 minutes. However, the optimal time in the chamber 10 and amount of radio-frequency waves for a particular facility will vary and may be determined as described in "Validation." Another embodiment of the invention as shown in FIG. 2 arranges the heating elements (for example, the radio-frequency generating system of exciters and grounds) inside the gamma radiation chamber 20 for simultaneous exposure of the medical materials to heat or radio-frequency waves and gamma radiation. Another embodiment of the invention orients the heat or radio-frequency chamber with respect to the gamma radiation chamber so that the medical material is first exposed to gamma radiation and then heated. Another embodiment of the invention shown in FIG. 2 employs a system of tracks and/or conveyor belts 4 to move medical or veterinary waste from the sterilization chambers to the shredders 30. The foregoing descriptions of the preferred embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many other modifications and variations are possible in light of the above teachings. The embodiments were chosen and described to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to best utilize the invention in its various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims, including all equivalents.