Method and apparatus for photopyrolitically removing a contaminant

A method for safely removing a contaminant from a substrate surface without the need for any precoating of the substrate. Because the resultant molecular decomposition of the contaminant occurs relatively faster than heat transfer to the underlying substrate, substantially no substrate heating results. The light source is preferably a xenon flash lamp operated with a pulse repetition rate of between about 0.1 pulses/second and 12 pulses/second, an energy pulse duration of about 400 microseconds to about 800 microseconds, and a peak energy per pulse exceeding about 3,750 joule. Ultraviolet elements of the spectrum produced by the flash lamp are reduced or eliminated by the use of filters or reflectors that absorb or otherwise eliminate ultraviolet light. The substrate to be decontaminated may be the exposed surface of a living animal or plant or may be protective clothing or a vehicle contaminated with chemical or biological agents. The method also provides a two-step process for decontamination of a substrate surface followed immediately by "finishing" of the surface to produce a smooth, finished surface.

FIELD OF THE INVENTION
 This invention relates to removal of a contaminant from a substrate
 surface, and more specifically to the safe disintegration and removal of a
 contaminant from a substrate surface using components of the light
 spectrum, without pre-coating the contaminant or substrate.
 BACKGROUND OF THE INVENTION
 The safe and efficient removal of contaminants from an underlying substrate
 surface can present a formidable challenge. Frequently the contaminants
 include materials that if not themselves hazardous, can become hazardous
 during a decontamination process. In addition, the decontamination process
 should not weaken or substantially damage the structural integrity of the
 underlying substrate. The design of a system for safely removing
 contaminants must concern itself with the potential exposure of removal
 personnel to hazards, cost of the system, the cost of any protective gear
 required to be worn by those using the system, the cost of the labor
 required for the decontamination process, and the cost of disposing of
 decontamination process byproducts.
 As used herein, the term "contaminant" need not designate a material that
 is intrinsically harmful. For example, a coating such as paint, whose
 removal from an underlying substrate is desired, may be deemed a
 contaminant. Since filing the previous application (U.S. Ser. No.
 8/748,185) the applicant has discovered that, the term "decontaminatable
 contaminant", in the context of the present invention, may also include,
 by way of example, biological organisms and chemical and biochemical
 agents such as pathogenic bacteria and viruses, neuro-toxic agents and
 biological toxins.
 One commonly used prior art approach has been to blast the contaminants
 away with abrasive particles such as sand or plastic beads. While the
 equipment required to practice this approach is relatively inexpensive,
 this process is highly labor intensive, requiring protective masking of
 adjacent substrate regions and the wearing of protective garments by the
 work crew. During decontamination, considerable grit and/or particulate
 dust is present. This particulate matter often dictates that adjacent
 electrical generators and similar equipment be shutdown and protected, the
 downtime representing an additional economic burden imposed by abrasive
 decontamination systems.
 In many applications, abrasive decontamination processes must be performed
 within an enclosed housing, which requires that the substrate be brought
 to the housing. This requirement can be burdensome where, for example, the
 substrate is large or cumbersome, the hull of a seagoing vessel, for
 example. Further, abrasive processes are slow, typically being on the
 order of less than one square foot per minute. Further, the structural
 integrity of the substrate being decontaminated may be weakened due to
 dimpling or stretching from impact with the abrasive particles. Finally,
 after decontamination is complete, a considerable volume of contaminated
 grit, including for example water, CO.sub.2, plastic media and the like,
 must be safely disposed of, thus imposing a burden on existing landfill
 resources.
 A second commonly used prior art approach is the use of chemical agents to
 remove contaminants such as undesired paint, methylene chloride being a
 commonly used agent. Unfortunately chemical agent techniques are even more
 labor intensive than abrasive techniques, requiring extensive preparation
 and clean-up after stripping, requiring perhaps 250 man-hours to
 decontaminate the exterior of a commercial airliner. Further, the
 personnel performing the decontamination must be provided with costly and
 cumbersome protective full body suits and breathing apparatus. Finally,
 chemical decontamination process byproducts can include hundreds of
 gallons of contaminated water and often methylene chloride, for which the
 cost of safe disposal can be quite high. At present there are few options
 available with regard to a chemical stripping agent that is effective and
 safe. Methylene chloride, for example, is expected to be banned by the
 United States Environmental Protection Agency from future use due to its
 release of ozone-depleting chlorofluorocarbons ("CFCs").
 A third prior art approach is the removal of contaminants using high
 intensity visible spectrum light energy. For example, as disclosed in U.S.
 Pat. No. 4,867,796 to Asmus, et al., the contaminant is first precoated
 with an energy absorbing medium, and then subjected to pulses of high
 intensity light energy. The medium absorbs the light energy, which is
 converted to heat causing the contaminant to decompose and/or be
 vaporized, thus removing the contaminant from the substrate. The heat
 generated by the short duration light energy pulses is localized at the
 contaminant surface and is safely dissipated by the accompanying
 contaminant vaporization without substantially affecting the substrate.
 Interestingly, it has long been held in the prior art that energy pulses
 exceeding about 20 Joule/cm.sup.2 are undesirable as tending to unduly
 heat and stress, if not combust, the underlying substrate.
 While Asmus-type systems are especially promising commercially, the need to
 precoat the substrate before decontamination is time consuming, costly,
 and potentially hazardous. For example, workers performing the
 decontamination process are exposed to potentially hazardous contaminants
 during precoating. Even if the contaminant being precoated is
 non-hazardous, the areas to be precoated may be difficult or dangerous to
 reach, a very high ceiling, for example. After decontamination the problem
 remains of how to safely dispose of hazardous contaminants once they have
 been removed from the substrate using light energy. Finally, the thermal
 energy associated with Asmus-type decontamination systems can cause even
 non-hazardous contaminants to breakdown into sub-components that are
 hazardous and require safe disposal.
 To summarize, what is needed is an apparatus and method providing safe and
 efficient decontamination, without damaging the substrate and without
 requiring that the contaminant be precoated. Preferably the apparatus and
 method should result in the removed contaminant being reduced to
 constituents that are relatively non-hazardous, and should provide a
 mechanism for containing and removing such constituents from the work
 site. Further, safe and efficient decontamination should be provided
 without requiring personnel performing decontamination to wear expensive
 and cumbersome bodysuits and breathing apparatus.
 Additionally, there is a need for an apparatus and method for
 decontaminating selected areas of a surface without pre-coating the
 surface, especially on a relatively small scale, such as the scale of a
 circuit board or a computer chip. For instance, on a surface on which a
 pattern is present, which pattern may include different materials and/or
 colors, application of light energy would result in differential
 absorbtion of the light energy, creating photopyrolytic effects. This
 would cause decontamination in certain areas but not in others.
 Also, there is a need for an apparatus and method for decontaminating and
 "finishing" selected areas of a surface without pre-coating the surface.
 The process of finishing creates a relatively smooth surface. A finished
 surface can be physically more resilient than a rough or irregular surface
 and a finished surface is more amenable to cleaning and removal of dust
 and other particles, which is important in the operation of certain
 electronic equipment. A finished surface can be likened to a polish ed
 surface in marquetry, the boundaries between areas composed of different
 materials is smoothed over to present a continuous, smooth surface.
 Finishing may involve bonding of surface molecules to one another.
 Also, there is a need for an apparatus and method for ridding substrate
 surfaces of biological, biochemical or chemical agents which may be toxic
 to man or animals or plants and wherein said substrate surface is present
 on a subject that may include a vehicle, protective clothing or skin or
 the exterior of an animal or plant. There is a need for such an apparatus
 and method wherein the subject is not physically touched by a solid
 object, such as a brush, and whereby the subject is not subject to damage
 by such a process.
 The present invention provides such an apparatus and method.
 SUMMARY OF THE PRESENT INVENTION
 The present invention provides a photopyrolitic process and apparatus
 whereby one or more contaminants on a substrate surface is safely removed
 without having to first precoat the contaminants and without substantially
 damaging the underlying substrate. The present invention also provides a
 means of decontaminating a substrate and/or finishing the substrate
 surface by exposure to two or more different wavelengths and amplitudes of
 light. Without limitation, the contaminants that may be so removed can
 include PCBs and nuclear material, as well as coatings such as paint, and
 may also include biological, chemical and biochemical contaminants.
 In a first aspect, the present invention provides a system that includes a
 light source including a flashlamp whose energy output spectrum includes
 visible and infrared components, and an energizer that powers and triggers
 the light source. The energizer is operator controlled such that the light
 source's average energy output power, energy pulse width, and energy
 repetition rate are varied to best remove a contaminant from a substrate.
 Preferably a mechanism is provided for selectively filtering the light
 source output to emphasize a chosen region of the output spectrum.
 The thus tailored energy output spectrum is selected to be advantageously
 absorbed by the contaminant to be removed, thereby promoting efficient
 removal. For example, where the contaminant is paint, ultraviolet output
 energy is preferably suppressed by coating the flashtube with a doping
 agent such as cerium-oxide or silver to restrict ultraviolet spectral
 components. The paint absorbs components from the remaining energy
 spectrum, whereupon decontamination proceeds photopyrolitically, without
 subjecting personnel to possibly dangerous ultraviolet exposure. By
 contrast, in a bio-remediation task, ultraviolet components are desirable.
 Bursts of energy from the light source heat the contaminant sufficiently to
 remove it from the substrate without substantially heating the substrate.
 In contrast to the prior art, the levels of energy employed in the present
 invention exceed what has hitherto been regarded as an upper limit, beyond
 which the substrate would be stressed and otherwise harmed. The
 contaminant appears to carbonize directly, being reduced to ash apparently
 without entering a melt phase. This process appears to occur at a rate
 faster than the majority of the heat associated with the carbonized
 contaminant can transfer to the substrate, thus minimizing heat buildup on
 the substrate surface. No precoating of the contaminant is required.
 The light source preferably is mounted within a lamp head that is
 surrounded by a vacuum. As the lamp head is moved across the substrate,
 target regions of contaminant become carbonized and the resultant ash and
 gas byproducts are simultaneously drawn away by the vacuum surrounding the
 lamp head for safe disposal.
 The light source is preferably partially surrounded by a bifurcated
 aerodynamic reflector that focuses the pulsed energy output onto the
 target contaminant and also promotes light source cooling. The reflector
 configuration is aerodynamic in the sense that an associated cooling
 airstream blows decontaminat i on byproducts away from the focal region of
 the light source, thus maintaining an effective high output light energy
 level. According to the present invention, the lamphead may be handheld
 for movement across the substrate . Alternatively, a robotic arm mechanism
 can hold and move the lamphead across the substrate for decontamination.
 This is especially advantageous where the lamphead dwell time on a given
 substrate area is relatively long, during vitrification, for example.
 In a second aspect, a method of decontamination is disclosed. The method
 calls for subjecting the target contaminant to a high train of light
 pulses whose average energy level, pulse width and pulse repetition rate
 are selected to heat and carbonize the contaminant without substantially
 heating the underlying substrate. Preferably the light pulses include
 components in the visible light spectrum, in the ultraviolet light
 spectrum and near infrared ("IR"), and the method permits favoring a
 desired spectral region to promote more efficient decontamination.
 Simultaneous with the contaminant heating, the method preferably vacuums
 away decontamination byproducts, which may then be filtered and safely
 disposed of.
 Since prior U.S. application Ser. No. 8/748,185, which was filed on Nov.
 12, 1996, applicant has discovered that the concept of a "decontaminatable
 substrate" may include clothing, skin, animals, plants, vehicles (and
 other objects) that may have been contaminated with biological and/or
 chemical agents. Applicant has also discovered that light energy may be
 used to finish a surface, to produce a smooth surface, as well as to
 ablate or decontaminate the surface. Applicant has also found that light
 energy may be used to promote useful formation of chemical bonds as well
 as to break chemical bonds on a surface or in a gaseous environment.
 Applicant has also found that light energy may be used to differentially
 decontaminate a patterned surface wherein the pattern consists of two or
 more colors or materials which preferentially absorb light of different
 wavelengths. Applicant has also found that light energy may be used to
 effectively clean graffiti composed of paint, and other pigments from
 surfaces such as walls and the sides of vehicles such as busses and subway
 trains.
 In a third aspect, a method is disclosed for decontaminating selected areas
 of a surface without pre-coating the surface, such as on a surface on
 which a pattern is present, and where that pattern consists of different
 materials or colors. In this case, application of light energy would
 result in differential absorbtion of the light energy, creating
 photopyrolytic effects which would cause decontamination in certain areas
 but not in others.
 In a forth aspect, a method is disclosed involving decontamination of a
 surface followed by "finishing" of the surface by the application of
 different wavelengths of light. In this embodiment the first light
 exposure that causes thermal decontamination consists of visible and/or
 infa-red wavelengths generated by a flash-tube, and the second exposure,
 that causes finishing, consists of relatively low-energy, ultra-violet
 wavelengths generated by a continuous wave ultraviolet source with a
 relatively lower power output, such as about 60 W.
 In a fifth aspect, a method is disclosed for decontaminating substrates
 contaminated with biological, biochemical or chemical agents which may be
 toxic to man or animals or plants. Such agents may include bacteria,
 bacterial spores, toxins, viruses and nerve agents and caustic agents and
 psychoactive agents. Substrates, in this case, may include vehicles,
 protective clothing or the exposed surface of an animal or a plant. In
 this case decontamination is done using light energy free of ultraviolet
 wavelengths. Rapid increases in skin surface temperature and possibly
 other effects of light energy are sufficient to kill organisms but the
 duration of the temperature increase is so short as to cause no harmful
 effects or pain to the subject.
 Other features and advantages of the invention will appear from the
 following description in which the preferred embodiments have been set
 forth in detail, in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 FIG. 1 depicts a system 2 according to the present invention as preferably
 including a handheld light source unit 4 that is coupled via an umbilical
 6 to a portable console unit 8. Console unit 8 receives typically 220 VAC
 power from an external source and internally includes a high voltage power
 supply 10, a pulse forming circuit 12, and a cooling system 14. Preferably
 electrical signals and cooling water from these various elements are
 coupled to light source unit 4 via a Canon-type connector 16. Unit 18,
 shown generically in FIG. 1, provides pressurized air into light source
 unit 4 via hose 20A at about 150 ft.sup.3 /minute. Although it need not be
 located physically within unit 18, the present invention further includes
 a vacuum-generating mechanism that creates about 350 scfm (via hoses 20B)
 within light source unit 4. It will be appreciated that a negative net
 pressure thus is created within unit 4 that advantageously prevents
 decontamination byproducts from escaping. Preferably, unit 18 provides a
 filtration receptacle 22 into which hoses 20B deposit vacuum-removed
 byproducts resulting from decontamination of substrate 34. More
 specifically, soot, debris and other decontamination byproducts resulting
 from the operation of the present invention, are vacuum-removed from the
 area covered by the light source unit 4 via pressurized air return hoses
 20B that lead into a suitable sealed receptacle 22 associated with system
 18. Of course, receptacle 22 could be located external to system 18.
 Preferably a HEPA-compliant filter system and/or carbon-activated filter
 is coupled in series with return hoses 20B, preferably near unit 4, to
 filter fine particulate matter. Further, the incoming pressurized air
 helps maintain a clean target region 32.
 Console unit 8 further includes a control panel 24 having operator controls
 26 and display readouts 28 for controlling the electrical power, and
 coolant from unit 8 via the umbilical 6 to the light source unit 4.
 Console unit 8 can also include controls governing operation of the
 external air/filtration system 18. Preferably console unit 8 is mounted on
 wheels for mobility and is about the size of a standard relay rack,
 weighing perhaps 600 pounds. Of course other configurations could be used
 for console unit 8. The external air vacuum system 18 typically includes a
 compressor and is about the same size as console unit 8. Of course, if the
 decontamination work site includes a permanently installed shop vacuum
 and/or air compressor system, system 18 need not include an air
 compressor.
 In brief, console unit 8 provides operator controllable electrical signals
 via umbilical 6 to the light source unit 4, which unit 4 is used to remove
 one or more contaminants 30 in a target area 32 from an underlying
 substrate 34. More particularly, light source unit 4 contains a flashlamp
 36, partially surrounded by a bifurcated parabolic reflector 38, that
 emits energy 40. The energy 40 is reflected and/or focused by the
 reflector 38, and removes one or more contaminants 30 from the target
 region 32, the decontamination byproducts preferably being removed via
 return hoses 20B for deposit in receptacle 22.
 As used herein, target region 32 refers to the area of substrate 34 against
 which the light source unit 4 is positioned to remove contaminants 32 in
 that region. As depicted in FIG. 1, the substrate 34 may have any
 orientation and need not be planar. Further, contaminate(s) 30 need not
 have uniform thickness.
 As an alternative to being handheld, unit 4 may be mounted on a robotic arm
 42 that operates to mechanically move unit 4 across the substrate 34 and
 contaminants 30. Robotic movement of unit 4, preferably under programmed
 control of console 8, advantageously permits unit 4 to dwell over the same
 target area 32 sufficiently long to vitrify contaminants in certain
 applications.
 Vitrification is the process of melting contaminants into glass using heat.
 Vitrification may be performed on soils and surfaces contaminated with
 hazardous wastes, such as polychlorinated biphenyls (PCBs), for
 remediation of a waste site. A concrete cooling water pool associated with
 a nuclear power plant can be such a site. By permitting a relatively long
 dwell time over a target area (e.g., at least many seconds), the hazardous
 waste is solidified and stabilized in glass form for subsequent disposal
 or recycling. Encapsulation in glass form essentially removes the
 environmental threat otherwise associated with the waste. By contrast,
 hazardous wastes that do not undergo vitrification can leach from their
 original point of disposal and pose a continuing environmental threat.
 In the present invention, flashtube 36 can generate energy pulses in the
 3,750 joule range, an energy level at which flashtubes in prior art
 configurations typically disintegrate. Generating this energy produces
 significant heat that must be safely dissipated to promote flashtube 36
 longevity. It is therefore necessary to cool the flashlamp 36 with a
 circulating coolant, e.g., water, provided by cooling system 14.
 Because photons from flashlamp 36 ionize the circulating coolant water,
 cooling system 14 preferably includes a deionizer (not shown) to ensure
 that the cooling water surrounding the flashlamp is non-conductive, e.g.,
 deionized. The deionizer may, but need not be, mounted within console unit
 8. In the preferred embodiment, system 16 circulates water via the
 deionizer around flashlamp 36. The water circulates with a flowrate of
 about 5 gallons/minutes and maintains a temperature around the flashlamp
 of about 68 degrees F (20 degrees C).
 With reference to FIG. 2, this de-ionizing cooling water preferably is
 provided within the reinforced tubing shell of umbilical 6, coaxially
 about an electrical conductor 44 carrying high voltage signals from the
 pulse forming circuit 12 to the light source unit 4, all within umbilical
 6. Of course, the high voltage conductor 44 is surrounded by insulation
 46, a ground braid 48, and a high voltage outer jacket 50, which elements
 are then surrounded by the de-ionizing cooling water 52A and the
 reinforced tubing shell 54 whose inner diameter is about 1.25" (3.2 cm).
 Other configurations for providing high voltage and input cooling water
 may be used, however. Heated, ionized, water from light source unit 4 is
 returned to system 14 for cooling and de-ionizing via a return conduit
 52B.
 With reference to FIG. 2, light source unit 4 preferably includes a xenon
 flashlamp 36 that operates somewhat similarly to a lamp used in flash
 photography, except that unit 4's light output energy is several thousand
 times more intense. The xenon gas is contained within a quartz envelope,
 the gas and envelope together forming flashlamp 36 in the accompanying
 figures. The outer diameter of the flashlamp 36, e.g., collectively the
 gas and surrounding quartz envelope is about 12 mm. A preferred unit for
 flashlamp 36 is model VBX F10 manufactured by V.B.I. Technology, Inc.,
 located in Auburn, Calif.
 For ease of use, light source unit 4 may be handheld and preferably
 measures about 9" (23 cm) in length by about 5" (12.7 cm) in depth by
 about 3" (7.6 Kg) width and weighs about thirteen pounds (5.9 Kg),
 although other configurations could of course be used. Different light
 source units 4 may be used, without requiring system modification, to
 provide lamp heads with a longitudinal arc length L varying from about 6"
 (15 cm) to about 24" (61 cm).
 Xenon gas within the flashlamp 36 absorbs pulses of electrical energy
 provided by the pulse forming circuit 12 via umbilical 6 and electrical
 lead 44. When the flashlamp receives these pulses, the xenon gas releases
 its stored energy in the form of light particles, or photons and heat,
 depicted as arrows 40.
 The emitted light energy 40 will include visible, ultraviolet and infrared
 spectral components. Applicant believes that visible and infrared spectral
 components are associated with heating energy per se, whereas ultraviolet
 spectral components are associated with driving, or encouraging, chemical
 changes within the contaminant.
 According to the present invention, controls 26 are operator adjusted such
 that power supply 10 and pulse forming circuit 12 cause light source unit
 4 to be triggered, via umbilical 6, in a selected manner that causes
 flashlamp 36 to provide periodic pulse bursts of light energy having
 desired characteristics. If desired, similar controls could also be
 mounted on source unit 4. Such remote controls would be coupled via
 umbilical 6 to console 8 to permit remote operator control of the pulse
 forming parameters, without having to make adjustments at the console unit
 8 itself.
 The various controls permit decontamination personnel to vary, for example,
 the energy pulse width from about 400 micro-seconds to 800 micro-seconds
 (e.g., how long the light source will provide energy per each pulse),
 pulse repetition rate from about 0.1 to about 12 pulses/second, and the
 energy per pulse, from essentially zero to about 3,750 joules/pulse. This
 energy level is substantially higher than what the prior art regards to be
 safe with respect to heat damage to the substrate. Of course, other
 combinations of pulse widths, repetition rates and energy level/pulse
 could also be used.
 It will be appreciated that the product of the number of pulses and the per
 unit pulse energy determines the rate of decontamination of a given
 substrate and contaminant. Large per unit energy pulses having a low
 repetition rate are generally preferred over the use of faster repetition
 rate pulses with less per unit energy since the former will accomplish the
 decontamination task sooner.
 FIG. 3A depicts a generalized schematic of the pulse forming circuit 12,
 and related circuitry for powering flash lamp 36 in unit 4, whereas FIG.
 3B depicts voltage versus time wave forms at various nodes in the
 schematic of FIG. 3A. The input voltage to the circuitry of FIG. 3A is
 provided by power supply 10, which preferably operates from three-phase
 220 VAC. Nominally, power supply 10 provides an output rated at 40 kW, 5
 kV peak output. Further, step-up or step-down transformers may also be
 utilized to accommodate the power at hand. Of course in remote locations
 where 220 VAC is not available, an electrical generator of perhaps 5 to 10
 horsepower could be used to provide input power for power supply 10.
 Power supply 10 is preferably implemented using resonant inverter switching
 power supplies using insulated gate bipolar transistors ("IGBTs").
 Preferably one such inverter is operated as a master power supply module,
 with two additional inverters being slaved to the master module.
 Collectively, power supply 10 provides a peak 5 kV DC output with a rating
 of about 45,000 Joules/second, and supports operation of flashtube 36 at
 12 pulses/second or more. Because the design of power supply 10 will be
 known to those skilled in the art, detailed schematics are not here
 provided.
 With reference to FIG. 3A, the nominal 5 kV output from power supply unit
 10 is coupled via lead 46 to the pulse forming network unit 12. As shown
 therein, unit 12 includes pulse shaping capacitors C1-C3 and inductors
 L1-L3, formed in a three section pi-network. In the preferred embodiment,
 capacitors C1-C3 are each about 100 micro F and inductors L1-L3 are each
 about 64 micro H.
 FIG. 3B shows the voltage wave forms present at nodes A, B, C and D in FIG.
 5A. As shown therein, the peak capacitor voltages at nodes A, B, C are
 about 5 kV nominal, which provides an energy storage of about 3,750 Joules
 per pulse of flashtube 36. The baseline of the wave forms for nodes A, B
 and C indicates minimal reverse voltage on capacitors C1-C3.
 The output of pulse shaping unit 12 is switched into the light source unit
 4 via three series-coupled silicon controlled rectifiers (depicted
 collectively as "SCR" in FIG. 3A), which are transformer driven from a
 single field effect transistor. The present embodiment uses 20 kV rated
 TR2012 SCRs, manufactured by the EG&G Company, located in Salem, Mass. The
 pulse shaping unit output is coupled via lead 44 to the input of flashlamp
 36, and attains about 2.4 kV with a peak current of about 3.13 kA at 120
 micro-seconds. This peak current corresponds to i, which is approximately
 equal to CdV/dt, where C=100 micro F, dV is approximately equal to 2 kV
 and dt is approximately equal to 100 microseconds. At about 12 Hz
 repetition rate, the output waveform represents about 204 A RMS.
 When the present invention is first turned on, for example at the start of
 the work day, an initial power-up signal is provided by console unit 8. As
 shown by FIG. 3A, this signal is coupled via lead 58 to a flashlamp
 trigger circuit 60 that provides a high voltage, short duration lamp
 trigger pulse to initiate conduction of flashlamp 36. This signal is
 coupled via lead 61 to unit 4 and conventional circuitry within the
 flashlamp trigger 60 and, at power-on, provides a typically 30 kV, 1.5
 microseconds full width half measure ("FWHM") pulse to flashlamp 36 to
 initiate conduction. Within unit 4, an SCR and step-up pulse
 auto-transformer couple this start-up pulse to an external electrode 62
 disposed axially along side flashlamp 36.
 As noted, flashlamp trigger 60 initiates conduction of flashlamp 36, but
 thereafter pulses coupled via lead 44 fire flashtube 36, under operator or
 console unit 8 control. However to minimize stress on flashtube 36, the
 pulse forming circuit 12 preferably includes a simmer circuit 64 that
 maintains a continuous conductive flashlamp state. Simmer circuit 64 is
 preferably current regulated and provides a nominal no-load 3 kV and a 1A
 trigger current to the flashlamp 36. Thus, as shown in FIG. 3A, the
 voltage waveform at lead 44 is nominally about 3 kV with a peak voltage of
 5 kV. The width of the 5 kV pulse determines the width of the energy pulse
 provided by flashlamp 36, and the repetition rate of the 5 kV pulse
 determines the repetition rate of the flashtube. Because the design of
 simmer circuitry is known to those skilled in the art, further details are
 not provided here.
 To promote operator safety, a fault detection circuit 66 includes a simmer
 current threshold interlock that inhibits charging the pulse forming
 network 12 when the flashlamp simmer current falls below an internally
 adjustable level.
 Understandably, because lethal power levels are employed, the present
 invention includes various safety features to protect operating personnel.
 For example a manual crowbar 68 comprising a shorting stick and a dump
 resistor R permit absorbing of the full energy of the pulse shaping
 capacitors C1-C3 three successive times, should immediate shutdown of
 system 2 be required.
 Further, a pair of automatic crowbars 70 coupled to fault detection
 circuitry 66, automatically shuts down the system under fault conditions.
 Crowbars 70 preferably comprise a ROSS Engineering high voltage relay and
 associated dump resistor.
 Those skilled in the art will appreciate that good pulsed-power practice
 requires minimum discharge loop areas, single point grounding and adequate
 filtering of incoming power and signal lines. Because the present
 invention is implemented with a single point ground node 72, the only
 current normally flowing through this node would be displacement current
 from stray capacitive and inductive coupling, occurring during a pulse
 discharge. Thus, a current monitor within circuitry 66 monitors current
 flow through node 72, and in the event of a flow greater than a desired
 threshold, the automatic crowbar 70 will shutdown system 2 until reset.
 Further, circuitry 66 also detects excessive output current and terminates
 pulse generation by unit 12 to safeguard system 2. As depicted in FIG. 3A,
 ground as well as the other electrical connections preferably are made to
 unit 4 via a connector 74. Line 76 in FIG. 3A couples control signals
 between unit 4 and a controller within console unit 8.
 It will be apparent from these figures that system 2 includes a mechanism
 for grounding light source unit 4 and returning discharged electrical
 currents from flashlamp 36 to the console unit 8 and power supply unit 10.
 In addition to promoting safety, the present invention advantageously
 reduces the generation of unwanted electromagnetic interference radiation
 ("EMI") and radio frequency interference radiation ("RFI") by using a
 single point grounding mechanism and by using coaxial connections to the
 flashlamp electrodes.
 When system 2 is properly adjusted by the decontamination personnel, bursts
 of energy 40 from flashlamp 36 appear to be at least partially absorbed by
 contaminant(s) 30 in the target area 32, and are converted into heat.
 Proper system adjustment entails adjusting the energy pulse width and/or
 repetition rate, average energy level, and preferably optimizing the
 spectral output of the emitted light energy for the contaminants at hand.
 When properly adjusted, emitted energy at the contaminant can reach 2,000
 degrees C or so, albeit for an extremely short time period. These short
 burst of intense heat appear to transform the contaminant from a solid
 phase to a combination of gases and typically whitish ash, without
 entering a melt phase. As such, the contaminant molecules appear to absorb
 components of the light source energy spectra directly and carbonize
 (e.g., decompose or reduce to ash), without the need for precoating with
 an absorbing agent, as disclosed in the Asmus, et al. patent.
 The heat produced by applicant's photopyrolitic system is believed to
 decompose even hazardous contaminants into lower molecular weight
 molecules. The ash byproduct in applicant's method is usually, but not
 always, whitish in color, with substantially no smoke being present. By
 contrast, a blackish ash and smoke byproduct are believed indicative of
 partial decomposition, probably due to incomplete degradation accompanied
 by a chemical reaction from overheating the contaminant.
 Molecular decomposition occurs relatively faster than the accompanying heat
 can transfer from the contaminant to the substrate. Stated differently,
 the rate of contaminant decomposition (that is, reduction to a lower
 molecular weight) occurs at a faster rate than heat can be conducted to
 the next exposed layer of decontaminated substrate. Thus, the substrate
 undergoes minimal heating or thermal loading, with essentially no adverse
 effect upon the substrate structural integrity. For example, it appears
 that while the contaminant temperature in target region 32 can briefly
 reach 2,000 degrees C or so, the underlying substrate temperature only
 increases about 17 degrees C to 28 degrees C. In this fashion, while the
 present invention employs energy levels substantially higher than what has
 been believed safe in the prior art, decontamination proceeds efficiently
 without apparent heat damage to the underlying substrate.
 With further reference to FIG. 2, when the flashtube 36 is triggered, the
 emitted light energy 40 is focused by reflector 38 upon target region 32.
 Reflector 38 is mounted upstream of flashlamp 36, and has preferably a
 truncated bifurcated aerodynamic shape. In the preferred embodiment,
 reflector 38 defines a truncated ellipse, although other configurations
 are possible, the goal being to focus emitted light energy upon the target
 region of the substrate.
 In the preferred embodiment, pressurized air from system 18 is caused to
 flow through the bifurcation region of the reflector 38 as noted by the
 "hollow" arrows in FIG. 2. This airstream helps cool the flashtube 36, and
 also maintains the target region 32 relatively free of ash and debris
 (shown as x in FIG. 2) and other byproducts (shown as y). The resultant
 airflow within unit 4 essentially vacuum-removes x and y, which leave unit
 4 via outlet hose 20B to be deposited into receptacle 22 in system 18 (see
 FIG. 1). Because x and y are thus removed, flashtube 36 can deliver output
 energy 40 to the target region 32, relatively unimpaired by any
 intervening ash and debris.
 The pressurized air is preferably also provided to several wind jets 88
 located on the perimeter of light source unit 4. These jets deliver an
 airstream downward and toward the target area 32, to ensure that debris,
 gases, and other byproducts do not escape from unit 4. As such, jets 88
 promote the safe removal of these byproducts from unit 4, via hoses 20B,
 for safe deposit in receptacle 22. Because of the air turbulence
 advantageously created within unit 4, it suffices to mount jets 88 on the
 "front" side of unit 4, e.g., the side facing the direction towards which
 the unit is being moved. Of course jets 88 could be mounted on the "back"
 side as well.
 Reflector 38 has a highly polished silver coated reflecting surface. This
 surface is preferably produced using the so-called Raytheon twenty-two
 step process wherein the machined reflector surface is first polished and
 treated to ensure good adhesion of the subsequent plating. Next, a layer
 of copper is applied, then a layer of nickel, a layer of silver and then a
 protective coating. Reflectors made according to this process are made by
 the Kentek Company, located in Pittsfield, N.H.
 While applicant has also used a polished aluminum reflector, a silver
 plated surface provides superior performance due to its increased
 reflectivity. In side cross-section, the front-to-back dimension of the
 reflector is about 3.5" (8.9 cm), with the axis of the flashtube being
 located at the focal point, about 1.5" (3.8 cm) from the rear region of
 the reflector surface. See for example FIGS. 4A and 4B.
 Effective decontamination is a function of the characteristics and
 magnitude of the light energy 40 provided by flashlamp 36 to the target
 region 32, including the energy wavelengths. The wavelength of the emitted
 light energy 40 depends upon several factors including, without
 limitation, the flashlamp gas used (e.g., xenon), the pressure within the
 flashlamp, and the composition of the material in reflector 38 (preferably
 a highly polished silver coating). However light energy 40's spectral
 components may also be operator controlled somewhat for the
 decontamination task at hand by varying the pulse characteristics and
 operating potential provided by control unit 8.
 To promote a desired distribution of visible and ultraviolet radiation, the
 flashlamp 36 is preferably mounted within a doped outer quartz envelope
 member 82 (see FIGS. 4A and 4B) whose shape is a longitudinal cylinder. In
 the preferred embodiment, member 82 has an outer diameter of about 22 mm,
 an inner diameter of about 18 mm, and a longitudinal length approximating
 the length L of the flashlamp 36. Outer member 82 is preferably clear
 fused quartz or Suprasil, a synthetic quartz material that includes a
 material commonly known as sprasil that was doped with cerium-oxide during
 fabrication. V.B.I., Inc. of Auburn, Calif. is a manufacturer of units
 suitable for use as member 66 in the present invention.
 As shown by FIGS. 4A and 4B, the cooling deionized water 80 circulated by
 system 14 via conduits 52A and 52B circulates in the cylindrical space
 between the exterior surface of flashlamp 36 and the interior surface of
 the outer quartz member 82. Although electrode element 62 is depicted in
 FIGS. 4A and 4B mounted longitudinally immediately opposite the
 bifurcation region of reflector 18, element 62 may be longitudinally
 mounted in a different position, preferably close to the exterior surface
 of outer quartz member 82.
 Preferably member 82 is readily removed from the lamp unit 4 for
 replacement by a second member 82' (not shown) having a second set of
 characteristics resulting in a different distribution of ultraviolet,
 visible and infrared radiation 40. In the preferred embodiment, an
 operator can modify light source unit 4, going from a Suprasil to an
 undoped quartz member 66 in about five minutes. Further, a different lamp
 unit having a different arc length L may also be readily substituted.
 By experimentally filtering out ultraviolet components from the flashlamp
 output spectrum, applicants discovered that certain contaminants or
 coatings still decompose as fast if not faster than when ultraviolet
 components are present. By filtering out ultraviolet components,
 decontamination still occurs, with the advantage that work personnel are
 not subjected to potentially harmful ultraviolet radiation. That
 decontamination can occur in many applications without the requirement for
 significant ultraviolet energy components is a departure from what has
 been practiced in the prior art.
 Table I below briefly summarizes these findings, where the first three
 columns denote what spectra components were present, and the four column
 indicates whether decontamination was successful. Apparently visible
 spectrum components promote a more complete combustion, wherein there is
 essentially no smoke, a white ash, and little chemical reaction. By
 contrast, black ash and smoke byproducts seem to reflect partial
 decomposition, probably due to an incomplete ultraviolet degradation
 resulting in a chemical reaction that may or may not complete.
 TABLE I
 ultraviolet visible infrared removal
 yes yes no no
 no yes yes yes
 yes yes yes yes
 yes no yes no
 Alteratively, members 82, 82' may b e undoped but of varying grades of
 quartz to provide a spectrum filtering function. For example, commercially
 available T08 non-doped quartz has a transmission range from about 210 nm
 (ultraviolet) through visible and infrared regions up to 3.7 micro m, with
 absorption bands at about 240 nm (ultraviolet) and 2.72 micro m
 (infrared).
 The ability to readily exchange member 82 permits further flexibility in
 tailoring system 2's ability to safely and efficiently remove different
 types of contaminants. Light source unit 4 preferably includes various
 safety interlocks (not shown) to prevent personnel from receiving
 electrical shock while replacing member 82 or the flashlamp 36. Further,
 the present invention also provides a "deadman" --type switch (not shown)
 to deactivate flashlamp 36 when unit 4 is not held or otherwise in a
 working disposition.
 Further, the flashtube 36 may itself may be cerium-oxide coated to provide
 a desired spectrum filtering function. Commercially available M-382
 cerium-oxide doped fused quartz envelopes attenuate ultra violet below
 about 400 nm. Typically the nature of the coatings of contaminant to be
 removed will suggest what output spectrum energy should be used. For
 example, paint or contaminants containing epoxy or polyurethane react
 favorably to flashtube energy that includes ultraviolet components,
 components not filtered by quartz. However, according to the present
 invention a cerium-oxide doped flashtube appears to remove such
 contaminants, without substantial ultraviolet energy components, as well
 as would a quartz-filtered flashtube that emitted ultraviolet energy.
 Understandably, the present invention's ability to rapidly and safely
 remove such contaminants without the health hazard associated with
 ultraviolet energy will be appreciated by those skilled in the art.
 Experienced personnel using the present invention can tell from the noise
 level accompanying removal, from the color of the soot, and from the
 relative speed of the removal process whether system parameters have been
 well optimized for the removal task at hand. The energy output provided by
 the lamp unit may be varied via controls on console 8 to alter the output
 energy spectrum. For example, decreasing the output energy say 100% to
 perhaps 80% will shift the output spectrum from substantially visible
 light components toward the near infrared region.
 The noise or sound level present at light source unit 4 is preferably
 monitored with a sound detector unit 86 (see FIG. 2), whose output is
 preferably coupled to console unit 8. The level and characteristic of the
 monitored sound provides an indication of the effectiveness and rate of
 removal of contaminants. For example, when system 2 is providing energy
 pulses of a suitable pulse width, repetition rate , energy level and
 spectral content the detected sound will be different than when the
 various system adjustments are less correct. Similarly, if the system is
 optimized for removal of a certain type of contaminant and a different
 contaminant is suddenly encountered, there can be a discernible change in
 the detected noise level and/or characteristics.
 A less dense, more easily removed, contaminant may be characterized by a
 higher noise level. Thus, detecting the noise level at the light source
 unit 4 and feeding this information to the console unit 8 to vary, for
 example, the trigger characteristics can provide a closed loop feedback
 system to optimize system parameters for efficient decontamination.
 Alternatively, the system could be operated open loop, with the system
 operator examining the detected noise or frequency (on a meter or spectrum
 analyzer, for example) to manually vary system parameters to optimize
 decontamination.
 In contrast to prior art decontamination methods, personnel operating
 system 2 need not routinely wear protective body suits and/or special
 breathing apparatus. In applications where ultraviolet spectral energy is
 required, ultraviolet goggles should, however, be worn for eye protection
 against light energy from unit 4.
 FIG. 4A shows the beginning of decontamination according to the present
 invention, with unit 4 positioned over a desired target area 32 containing
 contaminant(s) 30. Flashlamp 36 is emitting light energy 40 which,
 according to the present invention, has carbonized the contaminant(s) in
 the target area, reducing the contaminant(s) to a typically whitish ash
 debris (depicted as "x") and gaseous and other byproducts (depicted as
 "y").
 The ash and byproducts x, y are essentially simultaneously withdrawn from
 the target area 32 and from the lamp unit 4 via conduits 20B as a result
 of the vacuum created by system 18. The ash and other byproducts are
 deposited into receptacle 22 for safe disposal. Although as shown in FIG.
 4A, there is ash x present in the target region 32, the air pressure and
 flow through and about the bifurcated reflector 38 maintains a relatively
 clear path for energy 40 from flashtube 36, as has been described. In
 addition, air flow from jets 88 on the exterior of unit 4 create an air
 flow tending to block escape of particles x or gas y from within unit 4.
 The "hollow" arrows in FIG. 2 depict the nature of the air flow within and
 without unit 4.
 In FIG. 4B, the operator (not shown) or the robotic arm 42 has moved unit 4
 downward to a new target region 32', leaving behind former target region
 32, now in a decontaminated condition, with contaminants) 30 removed from
 the surface of substrate 34. Thus, as one target region 32 is
 decontaminated, unit 4 is moved to a different substrate region 32' for
 decontamination. Wheels or coasting glide surfaces 90 (see FIG. 2) 90,
 promote movement of unit 4 across work area. FIGS. 4A and 4B also show
 optional rotating wire or horse-hair brushes 92 that may be incorporated
 into unit 4 to frictionally remove any residual from the surface of
 substrate 34. Thus, as one substrate region is carbonized, the resultant
 ash and byproducts x, y are vacuumed away for safe disposal within
 receptacle 22. As unit 4 is moved onto a new area 32' for decontamination,
 the former target area 32 is left in a substantially decontaminated
 condition.
 A brief description of what applicant believes to be the process by which
 even hazardous contaminants, for example polychlorinated bi-phenyl (or
 "PCB"), are reduced by the present invention to less hazardous
 sub-components will now be given. The present invention can heat a
 PCB-contaminated substrate to about 980 degrees C, whereas PCBs degrade at
 about 276 degrees C. When used to treat a PCB-contaminated substrate,
 which may in fact be soil or even oil, applicant believes that the present
 invention probably causes the bi-phenyls to break from the chlorine. The
 byproducts are vacuum removed, using the present invention.
 After decontaminating PCB-containing soil or oil, the byproducts could be
 further processed by the addition of calcium carbonate. The resultant
 chlorine molecule would then probably bond with the calcium carbonate,
 producing small amounts of carbon dioxide and possibly hydrochloric acid
 as by-products.
 Thus, the present invention provides safe and relatively fast
 decontamination without generating copious amounts of contaminated liquid
 or solid debris, and without imposing undue burdens on existing landfills.
 Further, even dangerous contaminants are safely broken down into
 sub-components that are reduced to a fine ash and may be readily disposed
 of in a safe manner. If desired, after decontamination the substrate
 surface 34 may be bombarded with meltable CO.sub.2 pellets, rinsed with
 water, or wiped with a rag.
 FIG. 5 shows decontamination of a patterned surface 100 wherein the pattern
 comprises areas of different colors (or of different materials) 110 on the
 surface of the substrate. In this case, by virtue of the pattern, light
 energy is differentially absorbed by different areas on the surface of the
 substrate. This differential absorbtion creates photopyrolytic effects in
 certain areas but not in others, thereby causing decontamination in
 certain areas but not in others. In this case, the output from a light
 source unit 4 as described herein, is directed towards a substrate surface
 100 that has not been precoated with a light-absorbing agent but has a
 patterned surface. The light source is preferably a pulsed light source
 which produces a spectrum of light substantially free of ultraviolet and
 capable of producing light energy sufficient to photopyrolitically
 decompose a contaminant.
 The invention may be used as shown in FIG. 6 to decontaminate and then to
 finish a surface. This is a two step process using two different light
 sources. First, the surface is exposed to the output from a flash-tube
 light source unit 4, as described herein, producing mainly visible and
 infa-red wavelengths. The light energy 40 is focused by the reflector 38
 onto the substrate 34. This exposure thermally ablates the contaminants 30
 from the substrate thereby decontaminating it. Second, the surface is
 exposed to a continuous wave, low-power electromagnetic radiation such as
 light source 120 of, for example, 60 W power, which produces a spectrum
 125 containing at least some measurable amount of ultraviolet light
 whereby the substrate surface undergoes physical changes that result in a
 smoothing of the substrate surface. This exposure "finishes" the surface,
 making it smoother. The continuous wave light source 120 may consist of
 any commercially available light source that produces an appreciable
 ultraviolet component (for example, 1% ultraviolet radiation) being well
 known in the art, such as fluorescent ultraviolet lamp. The inventor
 believes that the finishing effect involves photochemical catalytic
 processes which encourage the bonding together of molecules at the
 substrate surface. Preferably, the light sources are physically separate
 and not contained in a single housing. Preferably, the substrate is
 composed of a small object, such as a silicone chip 130, that is laid on a
 surface which may be moved, such as a conveyor belt 140 to position the
 substrate first below one light source and then below the other. The
 substrate is first positioned under the first light 4 source and exposed
 to this first source, and then is moved to be positioned under the second
 light source 150 and exposed to this second light source. The substrate
 may be concomitantly exposed to a gas atmosphere 160, said gas perhaps
 being ejected as a jet from a tube 170, said gas acting as a catalyst or
 as reagent or as a cooling agent. In the case of the gas atmosphere being
 a reagent, the light source may be used to catalyze reactions between the
 surface substrate and the gaseous reagent. In the case of the gas
 atmosphere being a catalyst, the gaseous catalyst may act to speed up or
 slow down the rate of a reaction, taking place at the substrate surface,
 wherein the input energy is supplied by the light source.
 The present invention may also be used to catalyze a reaction between one
 or more reactant materials at a substrate surface by providing a substrate
 surface, providing one or more reactant materials at the substrate
 surface, and then directing a desired portion of an output spectrum from a
 pulsed source of light energy upon the substrate surface with sufficient
 energy to catalyze a reaction between the reactant materials. The desired
 portion of the output spectrum may be substantially free of ultraviolet
 components and may include an infrared component and a visible light
 component, or it may contain a measurable amount of ultraviolet light such
 as for instance 1% ultraviolet radiation. A gaseous or particle suspension
 environment may be provided at the substrate surface, for instance by the
 use of a spray apparatus directing a spray towards the substrate surface.
 this gaseous environment may contain reactive or catalytic elements that
 facilitate the reaction at the substrate surface.
 The invention may also be used for the safe decontamination of protective
 clothing worn by a clothed human being 180, decontamination of a vehicle
 190, decontamination of the skin of a naked human being 200 or
 decontamination of an animal 210 or of a plant 220. FIG. 7 shows the
 invention used for such decontamination wherein the light source unit 4 is
 positioned so as to focus light energy upon the subjects to be
 decontaminated. These subjects, that provide the substrate surface to be
 decontaminated, may be contaminated with biological, biochemical or
 chemical agents which may be toxic to man or animals or plants. In this
 case decontamination is done using light energy 40 that is substantially
 free of ultraviolet wavelengths. It is believed that rapid increases in
 substrate surface temperature are sufficient to kill organisms but the
 duration of the temperature increase is so short as to cause no harmful
 effects or pain to the subject where the subject is an organism. By
 substantially free it is meant that the amount of ultraviolet is reduced
 to an extent practically and reasonable possible. For instance, the
 inventor has conducted tests involving the exposure of living human skin
 to light pulses that were filtered using a 380 nm cutoff filter, the
 subject suffering no discomfort or apparent ill effects. Such exposure
 decontaminates the skin surface without exposing the skin to potentially
 carcinogenic ultraviolet radiation.
 Modifications and variations may be made to the disclosed embodiments
 without departing from the subject and spirit of the invention as defined
 by the following claims.