U.S. patent application number 09/997694 was filed with the patent office on 2003-07-31 for methods of using chlorine dioxide as a fumigant.
Invention is credited to Cowley, Gerald, Dechant, Darrell L., Eltomi, Sameh F., Mason, John Y..
Application Number | 20030143111 09/997694 |
Document ID | / |
Family ID | 25544283 |
Filed Date | 2003-07-31 |
United States Patent
Application |
20030143111 |
Kind Code |
A1 |
Cowley, Gerald ; et
al. |
July 31, 2003 |
Methods of using chlorine dioxide as a fumigant
Abstract
The invention provides methods of using chlorine dioxide gas for
the fumigation of building spaces, heating ventilation and air
conditioning systems (HVAC, e.g., return supply ducts, heating and
cooling coils and the like), vehicles, office spaces, process
equipment, files, documents, mail, mail processing equipment,
industrial process equipment and consumer related items under safe
conditions.
Inventors: |
Cowley, Gerald;
(Mississauga, CA) ; Mason, John Y.; (Plymouth,
CA) ; Eltomi, Sameh F.; (Overland Park, KS) ;
Dechant, Darrell L.; (Westminister, CO) |
Correspondence
Address: |
BOWDITCH & DEWEY, LLP
161 WORCESTER ROAD
P.O. BOX 9320
FRAMINGHAM
MA
01701-9320
US
|
Family ID: |
25544283 |
Appl. No.: |
09/997694 |
Filed: |
November 30, 2001 |
Current U.S.
Class: |
422/37 ; 422/1;
422/123; 422/28; 422/3; 422/32; 422/5 |
Current CPC
Class: |
A61L 2/20 20130101; A61L
9/015 20130101 |
Class at
Publication: |
422/37 ; 422/1;
422/3; 422/5; 422/28; 422/32; 422/123 |
International
Class: |
A61L 009/00; A62B
007/08 |
Claims
We claim:
1. A method suitable for fumigating a large enclosed volume and
contents requiring fumigation and restoring habitability,
comprising the steps of: climatizing a volume requiring fumigation
containing contents; generating chlorine dioxide gas; introducing
the chlorine dioxide gas into the volume requiring fumigation;
distributing the introduced chlorine dioxide gas in the volume
requiring fumigation; maintaining a residual amount of the chlorine
dioxide gas within the volume requiring fumigation under
environmentally safe conditions at a level and duration permitting
gaseous penetration of included contents as required for
decontamination; and removing the chlorine dioxide gas from the
volume requiring fumigation, thereby fumigating the large enclosed
volume and contents and restoring habitability.
2. The method of claim 1 wherein the chlorine dioxide gas is
removed from the volume requiring fumigation with the same
equipment that was used to introduce the chlorine dioxide gas.
3. The method of claim 1 wherein the chlorine dioxide gas is
generated as a solution of chlorine dioxide gas in a liquid.
4. The method of claim 3 wherein the liquid is water.
5. The method of claim 1 wherein the chlorine dioxide gas is
introduced using an emitter.
6. The method of claim 5 wherein the emitter is a stripper.
7. The method of claim 1 wherein the step of climatizing the volume
requiring fumigation includes the step of adjusting the relative
humidity.
8. The method of claim 1 wherein the step of climatizing the volume
requiring fumigation includes the step of adjusting the
temperature.
9. The method of claim 1 wherein the step of climatizing the volume
requiring fumigation includes the step of avoiding exceeding the
dew point.
10. The method of claim 1 wherein the step of climatizing the
volume requiring fumigation includes the step of reducing the level
of illumination.
11. The method of claim 1 wherein the volume requiring fumigation
is a portion of a building.
12. The method of claim 1 wherein the volume requiring fumigation
is a vehicle.
13. The method of claim 1 wherein the step distributing the
introduced chlorine dioxide gas comprises using a heating
ventilation and air conditioning (HVAC) system.
14. The method of claim 1 wherein the volume requiring fumigation
is maintained substantially dark.
15. The method of claim 1 wherein the chlorine dioxide gas is
present in the introduced gas at a concentration of at least
90%.
16. The method of claim 1 wherein the chlorine dioxide gas is
present in the introduced gas at a concentration of at least
95%.
17. The method of claim 1 wherein the chlorine dioxide gas is
present in the introduced gas at a concentration of at least
99%.
18. The method of claim 1 wherein the same apparatus is used to
climatize the volume requiring fumigation and to introduce the
chlorine dioxide gas into the volume requiring fumigation.
Description
BACKGROUND OF THE INVENTION
[0001] Gas fumigation as currently practiced uses either ethylene
oxide (epoxyethane, ETO), formaldehyde, vaporized peroxide or
ozone. Each of these fumigants has disadvantages that limit their
utility in fumigating large volumes, e.g. buildings or vehilces.
Ethylene oxide is a flammable and explosive gas that is classified
as both a mutagen and a carcinogen. The use of ethylene oxide as a
fumigant requires extensive post detoxification and clean up
procedures. Formaldehyde is potentially explosive and an
occupational carcinogen. Moreover, it has poor penetrating ability.
The use of formaldehyde as a fumigant requires extensive post
detoxification and clean up procedures. Vaporized peroxide reacts
generally with all organic compounds in the environment to be
fumigated, thus having a high demand for fumigant. Vaporized
peroxide is effective in fumigating spaces of volume less than 1200
ft.sup.3. Ozone reacts generally with all organic compounds in the
environment to be fumigated, and has the shortest half-life of
these fumigants, making ozone even less suitable than vaporized
peroxide for the fumigation of large volumes.
[0002] Chlorine dioxide is recognized as an effective sterilant.
However, no guidance is available regarding the use of chlorine
dioxide for the fumigation of large volumes. Sodium hypochorite is
known to be useful and effective for scrubbing down surfaces.
However, such procedures using sodium hypochlorite are labor
intensive, affect appearance and integrity of materials scrubbed,
and are not as suitable for large scale use as are the gas methods.
Chlorine gas is also not suitable due to the health hazards, high
corrosivity of the gas, and the production of chlorinated organic
by-products.
[0003] Chlorine dioxide, which is a selective oxidant and a protein
synthesis deactivator, has been reported to be efficacious against
Bacillus subtilis (a gram positive, chemoorganotroph spore former
similar to Bacillus anthracis) under controlled laboratory medical
sterilizer conditions.
SUMMARY OF THE INVENTION
[0004] The present invention provides methods for the effective
large-scale use of chlorine dioxide to allow for gaseous
penetration of contents included within in a large enclosed volume
requiring fumigation and sterilization in an environmentally safe
manner. The present invention provides a method comprising the
steps of:
[0005] climatizing a volume requiring fumigation containing
contents;
[0006] generating chlorine dioxide gas;
[0007] introducing the chlorine dioxide gas into the volume
requiring fumigation;
[0008] distributing the introduced chlorine dioxide gas in the
volume requiring fumigation;
[0009] maintaining a residual amount of the chlorine dioxide gas
within the volume requiring fumigation under environmentally safe
conditions at a level and duration permitting gaseous penetration
of included contents as required for decontamination; and
[0010] removing the chlorine dioxide gas from the volume requiring
fumigation, thereby fumigating the large enclosed volume and
contents and restoring habitability.
[0011] In one preferred embodiment, the chlorine dioxide gas is
removed from the volume requiring fumigation with the same
equipment that was used to introduce the chlorine dioxide gas.
[0012] In one embodiment, the present invention provides a process
comprising producing chlorine dioxide by using an apparatus such as
a chlorine dioxide generator. In one embodiment, the chlorine
dioxide is generated directly as a gas. In another embodiment, the
chlorine dioxide is generated as a solution of chlorine dioxide gas
in a liquid. In one preferred embodiment, the liquid is water. In
an aqueous solution, chlorine dioxide solution equilibrium partial
pressure is optimally kept below about 26,000 ppmV.
[0013] The generated chlorine dioxide is transferred directly, or
alternatively, indirectly via a storage tank, to a high gas:liquid
ratio emitter. In one preferred embodiment, the emitter is an
apparatus such as a gas/liquid contactor having a high efficiency
mist eliminator and very low liquid/gas rates. In one embodiment,
the emitter is an apparatus such as a stripper.
[0014] The emitter is operated to maintain the gaseous chlorine
dioxide concentration substantially below the explosion limit of
chlorine dioxide in the air. Prior to generation of the chlorine
dioxide, the emitters are used with water alone to raise the
relative humidity in the volume requiring fumigation, with
adjustment of the temperature. Alternatively, the humidification
and fumigation can be done simultaneously using the same apparatus
by the appropriate adjustment in the temperature of chlorine
dioxide solution.
[0015] The treatment is conducted in reduced illumination,
preferably substantially dark, to minimize the decomposition of
chlorine dioxide to chlorine. The process is monitored with the use
of an infrared camera or similar device.
[0016] If the space to be fumigated contains materials that are
potentially susceptible to corrosion, the chlorine dioxide should
be of the highest possible purity. Specifically, chlorine gas
should be present in the introduced gas at a level less than about
5%, preferably less than about 0.5%. Suitably chlorine dioxide gas
is present at a concentration in the introduced gas of at least
90%, preferably at least 95%, and optimally at least 99%.
[0017] Once the desired relative humidity and temperature are
attained, then the variable generation rate of chlorine dioxide gas
is initiated. The initial rate is high to provide sufficient
chlorine dioxide to penetrate the various surfaces demands within
the volume requiring fumigation. This rate is predetermined to
accommodate the surface demand as well as to provide the initial
charge of the volume requiring fumigation to a predetermined
chlorine dioxide residual level. The chlorine dioxide generation
rate is then reduced appropriately to maintain the predetermined
chlorine dioxide concentration in the air of the volume requiring
fumigation for a predetermined time. This can be achieved by a
number of means, such as lowering the concentration of chlorine
dioxide in the solution that is fed to the emitter, or lowering the
flow rate of the chlorine dioxide solution to the emitter.
[0018] The maintenance level of chlorine dioxide gas concentration
is determined to compensate for the decay or loss rate from the
volume requiring fumigation. The volume requiring fumigation is
preferably to be at slightly negative pressure to areas outside of
it and efforts are made to seal off the volume through the use of
strippable sealant, such as foam that sets up hard. Once the
required time weighted average concentration and contact time are
attained, then the generation of chlorine dioxide is stopped.
[0019] The generator, storage and emitter are then purged with
fresh water. Once this is complete, the water is injected with an
alkalizing and dechlorinating agent or other functional chemistry
(e.g., ascorbic acid), that will absorb the chlorine dioxide. This
scrubbing solution is then fed to the emitter and with the blowers
still in operation, the emitter begins to scrub chlorine dioxide
out of the environmental air composition within the said volume
that has been fumigated. This process is continued until the
environmental air composition within the volume that has been
fumigated is returned to acceptable limits for reopening to the
exterior environment and rehabitation.
[0020] The emitters can be located inside or outside of the volume
requiring fumigation. However, it is highly preferred to locate the
emitter inside the volume requiring fumigation, since then no
contaminated air is allowed to leave the volume requiring
fumigation.
BRIEF DESCRIPTION OF THE DRAWING
[0021] FIG. 1 is a schematic illustration of one embodiment of the
present invention.
DESCRIPTION OF A PREFERRED EMBODIMENT
[0022] The present invention can be further understood by reference
to FIG. 1, which schematically illustrates one embodiment of the
invention. The invention is practiced using a chlorine dioxide gas
generator 100 that provides chlorine dioxide dissolved in water 180
directly 160, or alternatively, indirectly 140 via storage 200, to
a emitter 300 comprising a blower 320 that produces chlorine
dioxide gas in air 360 for treatment of building areas and/or a
heating, ventilation and air conditioning (HVAC) return air system
of a building 400.
[0023] The chlorine dioxide generator 100 receives an input 150
that is a mixture of city makeup water 140 and chemicals 120 or
130. Suitable mixing means are used to combine the city makeup
water 140 and chemicals 120 or 130. Metering means are used to
regulate the amounts and proportions of the city makeup water 140
and chemicals 120 or 130 that are combined. In the initial
climatizing stage of the process, water alone is provided to the
input 150 of the chlorine dioxide generator 100, in order to adjust
the relative humidity of the volume to be treated. In the second
stage of the process, chlorine dioxide precursor chemicals 120 are
combined with the city makeup water 140. Several chemical means of
generating chlorine dioxide, and their corresponding chlorine
dioxide precursor chemicals are known in the art, and the choice of
suitable means and chemicals is within the abilities of the skilled
artisan. Exemplary chemical means of generating chlorine dioxide
are disclosed in U.S. Pat. Nos. 4,689,169 (Mason et al.), 5,204,081
(Mason et al.), 5,227,306 (Eltomi et al.), 5,258,171 (Eltomi et
al.) and 5,965,004 (Cowley et al.), the teachings of which are
hereby incorporated by reference.
[0024] The output of the chlorine dioxide generator 100 can be
routed directly 160 to provide chlorine dioxide dissolved in water
180 to the emitter 300. Alternatively, the output of the chlorine
dioxide generator can be routed 140 to a storage means 200, from
which chlorine dioxide dissolved in water 180 can be routed to the
emitter 300.
[0025] The emitter 300 removes chlorine dioxide from the water and
delivers chlorine dioxide in air 360 by duct means to the volume to
be fumigated, in general, building areas and/or a HVAC return air
system. "Duct means" includes, but is not limited to, temporary or
permanent ductwork, pipes, hoses and the like. Water 380 recovered
from the emitter can be recycled and combined by mixing means with
city makeup water 140 and chemicals 120 or 130 to provide input 150
to the chlorine dioxide generator 100.
[0026] In a third stage of the process, the chlorine dioxide
generator 100, storage 200 and emitter 300 are flushed with water
alone. During a further stage of the process, detoxification
chemicals 130 are combined with water to provide the input to the
chlorine dioxide generator 100.
[0027] Monitoring and controlling the dew point within the volume
requiring fumigation is a significant aspect. During the process of
fumigation, steps must be taken to avoid condensation. Therefore
during the entire fumigation process the atmosphere within the
volume requiring fumigation must be carefully controlled using
space heaters or the HVAC system both to avoid over-humidification
and to regulate the temperature of the chlorine dioxide solution
fed to the emitter. Failure to control these factors can lead to
spot damage as well as a higher use to chlorine dioxide.
EXAMPLE 1
[0028] The environment within the enclosed volume of a trailer is
fumigated and restored to habitability as follows. Initially, the
environment is climatized to a temperature of 70-80.degree. F. and
a relative humidity of 60-80%. During treatment, chlorine dioxide
is introduced into the volume to be fumigated and maintained at a
residual level of 500 ppm V for 10 hours. In other embodiments, the
residual chlorine dioxide level is maintained at about 750 ppm V,
about 1000 ppm V or about 3000 ppm V and the treatment time is in
the range of about 8 to about 12 hours. Typically, if the enclosed
volume is 2280 ft.sup.3, air is suitably recirculated at 5 CFM. The
treatment is conducted in reduced illumination, preferably
substantially dark, to minimize the decomposition of chlorine
dioxide to chlorine. Suitably chlorine dioxide gas is present at a
concentration in the introduced gas of at least 90%, preferably at
least 95%, and optimally at least 99%.
[0029] If the space to be fumigated contains materials that are
potentially susceptible to corrosion, the chlorine dioxide should
be of the highest possible purity. Specifically, chlorine gas
should be present in the introduced gas at a level less than about
5%, preferably less than about 0.5% Efficacy is measured by percent
inactivation of Bacillus subtilis spores used as monitors. The
contents of the trailer are inspected to determine the
discoloration and functionality of all the material placed in
trailer, including drapes, chairs, files, mail and other documents
and computers. Apart from a slight discoloration, no discernible
effects on carpets, drapes, furniture and office equipment (e.g.,
copiers, computers, printers, etc.) are found. No chlorine is found
in the treated space after fumigation.
EXAMPLE 2
[0030] The environment within an enclosed volume was fumigated and
restored to habitability as follows. HVAC equipment is inspected
and fans readied. All filters are removed and burned. Cooling and
heating coils are sprayed with degreaser/detergent. The environment
is climatized for 2.5 hours to a temperature of 60-80.degree. F.,
suitably about 75.degree. F., and a relative humidity of 70-80%,
suitably about 75%. The pH of the city water is adjusted to 6.5-7.0
to allow the emitters to deliver free ClO.sub.2 into the air. The
building is sealed with strippable foam and air loss rate measure
and used to correct the calculated chlorine dioxide dosage needed
for fumigation.
[0031] Additional internal fans are placed in positions determined
by modeling to assist the HVAC in approaching ideal mixing.
Chlorine dioxide is introduced with an air flow rate of 2,000 CFM
and maintained at a level of 500 ppm for about 12 hours. The
initial charge of the enclosed volume with chlorine dioxide is
rapid to prevent any pathogens from reacting to the hostile
environment. Typically the chlorine dioxide in the enclosed air
rises to 7-14 ppm a few minutes and is greater than 30 ppm within
five minutes. Efficacy of fumigation is measured by percent
inactivation of Bacillus subtilis spores that are used as
monitors.
[0032] The equipment is converted to scrubbers by rinsing chlorine
dioxide and emitter with water alone followed by a mixture of
bisulfite and caustic in water that absorbs ClO.sub.2 and Cl.sub.2
The environmental air is detoxified for 28-32 hours or the exchange
of about 30-32 building volumes, in order to reduce chlorine
dioxide levels in the building air to less than about 0.1
mg/m.sup.3. It has been found that the chlorine dioxide levels
typically decay at a rate of about 100 ppmV per hour, depending on
the contents included within the volume requiring fumigation. The
volume requiring fumigation can be detoxified very quickly,
typically in about 5-6 hours.
[0033] The building air is recirculated with the air conditioning
on to lower the relative humidity to less than about 35%. The HVAC
heating and cooling coils are sprayed with chlorine dioxide and the
HVAC filters are replaced with new filters.
[0034] The present invention is not to be limited in scope by the
specific embodiments described herein, but by the appended claims.
The described embodiments are intended as illustrations of
individual aspects of the invention, and functionally equivalent
methods and components are within the scope of the invention.
Indeed, various modifications of the invention, in addition to
those shown and described herein will become apparent to those
skilled in the art from the foregoing description and accompanying
drawing. Such modifications are intended to fall within the scope
of the appended claims.
* * * * *