GB2118028A

GB2118028A - Decontaminating surfaces

Info

Publication number: GB2118028A
Application number: GB08307747A
Authority: GB
Inventors: Keith Boyer
Original assignee: Maxwell Laboratories Inc
Current assignee: Maxwell Technologies Inc
Priority date: 1982-04-05
Filing date: 1983-03-21
Publication date: 1983-10-26
Also published as: FR2524316B1; GB2118028B; FR2524316A1; GB8307747D0; DE3310117A1; CA1201865A

Abstract

Surfaces are decontaminated by application of a chemical substance capable of absorbing radiation in a predetermined frequency range to the contaminated surfaces, and irradiating the thus treated surfaces with radiation of the predetermined frequency range. The contaminant may be a chemical warfare agent e.g. malathion, the radiation may be emitted by a laser or flash lamp, and the chemical substance applied may be p-amino benzoic acid or ferrocine. The surface cleaned may be a glass surface.

Description

SPECIFICATION Photodecontamination The present invention relates to a method of decontamination and more particularly, to the photoremoval of chemical warfare (C.W.) agents and other contaminants.

One method of decontaminating a surface of a chemical deposit is to expose the surface to highintensity radiation until the energy absorbed decomposes or evaporates the chemical.

"Decontamination", as used herein, refers to detoxification, cleaning, and other processes by which a chemical is removed or its noxious qualities are neutralized. Vig, et. al., U.S. Patent No. 4,208,135 discloses a method of removing contaminants from surfaces by precieaning the surface and air, and then irradiating the surface with shortwave ultraviolet radiation in the presence of oxygen. Shortwave ultraviolet is generally defined by the wavelength range of 1 700 angstroms to 3000 angstroms. Di Vita, et al., U.S. Patent No. 4,028,080, discloses a similar method used to clean optical fibers.

A problem arises with respect to some C.W.

agents, as well as other chemicals, in that they strongly absorb radiation only in the deep vacuum ultraviolet region, below 2000 angstroms.

Vacuum ultraviolet radiation is strongly absorbed by air, and hence, irradiation of surfaces requires an evacuated chamber. However, it is not usually practical to place a surface in need of decontamination in an evacuated chamber.

Furthermore; the deep vacuum ultraviolet region is generally devoid of economical high-intensity radiation sources. Hence, large scale decontamination of surfaces exposed to such C.W.

agents is not feasible using known methods.

It is an object of the present invention to provide an improved method for decontamination that is applicable to contaminants which do not absorb strongly optical frequencies generated by readily available radiation sources.

In accordance with the present invention, an improved method of decontamination employs a chemical additive capable of absorbing radiation of wavelengths greater than that of vacuum ultraviolet. The additive may be mixed with the contaminant, or alternatively, disposed upon and in contact with the contaminant. The combined chemical system is then exposed to high-intensity radiation of a frequency range strongly absorbed by the additive until a contaminant is destroyed, altered, or removed by evaporation, decomposition or alternative process. A laser or flash lamp may be used to supply the highintensity radiation.

In instances where a contaminant cannot be destroyed, altered or removed removed readily by irradiation because the contaminant does not strongly absorb radiation from readily available sources, a chemical additive which is strongly absorbed by radiation from a readily available source may be added to the contaminant. The resulting contaminant/additive chemical system can be irradiated with radiation which is absorbed by the additive until decontamination is complete.

The contaminant may be a chemical deposit or film upon a surface, or may be in another form.

The contaminant may be a C.W. agent or any other substance the removal, alteration, or destruction of which is required. The additive strongly absorbs radiation characteristic of a predetermined radiation source. The radiation source may have narrow frequency spectrum, such as a laser, or a broad frequency range, such as a flash lamp.

The additive may be mixed with the contaminant, layered over the contaminant, or otherwise situated so that an energy transfer may take place between the additive and the contaminant. The transfer may be thermal. More specifically, the radiation absorbed by the additive may be converted to thermal agitation of the additive. Molecular collisions between the additive and the contaminant then lead to the thermal agitation of the additive.

Other energy transfer mechanisms are appropriate for specific contaminant systems. For example, radiation may induce vibrational or electronic excitation in the additive. The energy stored may be transferred by re-radiation or by collisions to excite molecules of the contaminant.

Depending upon the contaminant, the energy transfer may effect decontamination in a variety of ways. Thermal energy may result in the evaporation of the contaminant. Alternatively, the heat may lead to the decomposition of the contaminant. Heat or electron excitation may lead to the ionization of the contaminant. The ionized contaminant molecules may combine with other chemicals so that the noxious qualities of the contaminant are neutralized. The neutralizing chemicals may beprovided with the additive.

In. a preferred embodiment of the present inventiori, a solution of para-aminobenzoic acid (PABA) is added ta a contaminant such as a C.W.

agent. PABA solutions strongly absorb radiation in the near ultraviolet region and thus is amenable to many high-intensity radiation sources. The C.W.

agent/PABA system may be irradiated by means of a high-intensity radiation source. The radiation source may be a laser such as an excimer, dye or N2 laser. Alternatively, a high-intensity pulsed xenon flash lamp, or other incoherent flash lamp, may be used to irradiate the chemical system.

Once the radiation is absorbed, some manner of energy transfer occurs to the C.W. agent,leading to its photoremoval.

The PABA is particularly well suited for decontamination by means of a flash lamp, such as a xenon flash lamp. PABA which is widely used to protect human skin from ultraviolet rays from the sun, is widely available in large quantities and is nontoxic. PABA absorbs ultraviolet radiation over a broad section of the near ultraviolet region.

Hence, it is a safe and available chemical which is an efficient absorber of radiation over the frequency range of a flash lamp.

PABA is also well suited for absorbing the radiation of lasers. However, specific additives -may be more efficient energy absorbers in a narrow spectrum of a particular laser. For example, ferrocine might be used as an additive in conjunction with an argon-fluoride laser.

EXAMPLE Tests have been performed to evaluate the efficacy of the present method. PABA solution and malathion were mixed in a test tube and then layered on a glass slide. Malathion is a C.W. agent analog, which means that it behaves physically and chemically like many of the chemicals developed for chemical warfare. After evaporation of the solvents, a residue remained on the slide.

Slides of this type were irradiated with KrF laser pulses (248 nm). The residue was completely removed from the irradiated area. Removal was also complete when similar slides were irradiated with a Flashblaster. (Flashblaster is a highintensity pulsed xenon flash lamp developed by Maxwell Laboratories).

COMPARATIVE EXAMPLE In one set of control tests, pure PABA solution was deposited on a slide. The PABA was completely removed from the irradiated areas of the slides when exposed to either the Krf laser or the Flashblaster. In a second set of control tests, pure malathion was deposited on glass slides. The malathion residue was not removed when irradiated by either radiation source. These tests support the proposition that the method of the present invention permits the photoremoval of contaminants not always readily removable by economical radiation sources.

In accordance with the above disclosure, a method of decontamination is presented which allows the photoremoval of contaminants from surfaces. It is apparent that alternative chemicals may be applied. These chemicals may absorb in the near ultraviolet or other portion of the spectrum in which high-intensity radiation sources are economical and practical. Other embodiments are within the spirit and scope of the present invention.

Claims

1. A method of decontamination comprising: adding a chemical additive to a contaminant, said additive being characterized in that it absorbs radiation in a predetermined frequency range; and irradiating the resulting contaminant/additive system with radiation of said predetermined frequency range until decontamination is complete.

2. A method of cleaning a surface of a contaminant comprising: adding a chemical additive to the contaminant, said additive being characterized in that it absorbs radiation in a predetermined frequency range; and irradiating the contaminant/additive system with radiation of said predetermined frequency range until said surface is clean.

3. The method of Claim 1 or 2 further characterized in that said additive absorbs said radiation in the near ultraviolet region.

4. The method of Claim 1 or 2 further characterized in that said additive is a solution of para-aminobenzoic acid.

5. The method of Claim 1, 2, 3 or 4 further characterized in that said radiation is provided by a laser system.

6. The method of Claim 1,2, 3 or 4 further characterized in that said radiation is provided by a flash lamp.

7. The method af Claim 6 further characterized in that said radiation is provided by a pulsed xenon flash lamp.

8. A method of photodecomposing a chemical deposit comprising adding a chemical additive to said deposit, said additive being characterized in that it absorbs radiation of predetermined frequency range, and exposing the resulting deposit additive system to radiation of said predetermined frequency range until said deposit is decomposed.

9. A method of photoevaporating a chemical deposit comprising adding a chemical additive to said deposit, said additive being characterized in that it absorbs radiation of a predetermined frequency range, and exposing the resulting deposit additive system to radiation of said predetermined frequency range until said deposit is evaporated.

10. A method of destroying a first chemical comprising: mixing a second chemical with said first chemical, said second chemical being characterized in that it absorbs radiation of a predetermined frequency range; and exposing the mixture to radiation of said predetermined frequency range so that said first chemical is destroyed by the heat of the absorption of said radiation by said second chemical.

11. A method of destroying a first chemical comprising; adding a layer of a second chemical so as to contact said first chemical, said second chemical being characterized in that it absorbs radiation of a predetermined frequency range; and exposing the mixture to radiation of said predetermined frequency range until said first chemical is destroyed by the heat of the absorption of said radiation by said second chemical.

12. The method of Claim 10 or 11 further characterized in that said first chemical is a chemical warfare agent and second chemical strongly absorbs radiation from the near ultraviolet region.

13. The method of Claim 12 further characterized in that said second chemical is a solution of para-aminobenzoic acid.

14. A method as claimed in any preceding claim substantially as hereinbefore described in the Example.

1 5. A method as claimed in any one of Claims 1 to 13 wherein the contaminant is such that it does not strongly absorb radiation of frequencies to which air is transparent and wherein the additive does strongly absorb frequencies to which air is substantially transparent.