U.S. patent application number 10/166535 was filed with the patent office on 2002-10-10 for ultraviolet germicidal apparatus and method.
Invention is credited to Iseman, Michael Dee, Morgan, Dale R., Palestro, Richard P., Rosier, Donald Preston.
Application Number | 20020144601 10/166535 |
Document ID | / |
Family ID | 26776688 |
Filed Date | 2002-10-10 |
United States Patent
Application |
20020144601 |
Kind Code |
A1 |
Palestro, Richard P. ; et
al. |
October 10, 2002 |
Ultraviolet germicidal apparatus and method
Abstract
A germicidal method and apparatus for destroying airborne
pathogenic bacteria such as tuberculosis bacteria using ultraviolet
light. Air is drawn through a filter and into a sterilization
chamber that is irradiated with ultraviolet light, and out through
an exhaust opening. Consideration for the characteristics of the
room in which the apparatus is installed and the positioning of the
installation allows effective prevention of transmission of disease
through expectoration and inhalation of airborne microdroplets of
bacteria-containing sputum. The filter is of the low-density type
which traps large particulates, but not small particulates of the
size of the microdroplets, so that the filter does not become a
bacteria colonization site. Baffles on the air intake opening and
air exhaust opening to prevent ultraviolet light from escaping into
the environment. The sterilization chamber is constructed such that
the air passes the ultraviolet light bulbs twice as it circulates
therethrough.
Inventors: |
Palestro, Richard P.;
(Aurora, CO) ; Morgan, Dale R.; (Aurora, CO)
; Iseman, Michael Dee; (Englewood, CO) ; Rosier,
Donald Preston; (Arvada, CO) |
Correspondence
Address: |
Glenn K. Beaton
Gibson, Dunn & Crutcher LLP
Suite 4100
1801 California St.
Denver
CO
80202
US
|
Family ID: |
26776688 |
Appl. No.: |
10/166535 |
Filed: |
June 10, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10166535 |
Jun 10, 2002 |
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09911340 |
Jul 23, 2001 |
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09911340 |
Jul 23, 2001 |
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08293153 |
Aug 18, 1994 |
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6264888 |
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08293153 |
Aug 18, 1994 |
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08087178 |
Jul 2, 1993 |
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08087178 |
Jul 2, 1993 |
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07960085 |
Oct 9, 1992 |
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Current U.S.
Class: |
95/273 ;
96/224 |
Current CPC
Class: |
A61L 9/20 20130101 |
Class at
Publication: |
95/273 ;
96/224 |
International
Class: |
B01D 046/00 |
Claims
What is claimed is:
1. A method for destroying airborne tuberculosis bacteria in air in
a room having a set of walls and a ceiling panel, comprising
mounting a device behind a wall or ceiling panel of the room,
filtering the air using a filter mounted on the device, drawing the
air through a sterilization chamber in the device having at least
one ultraviolet light bulb for irradiating the air with germicidal
ultraviolet light such that the air passes the light bulb twice,
and releasing the air including destroyed bacteria back into the
room.
2. The method of claim 1, wherein the filter traps substantially no
particulates and droplets smaller than 10 microns in diameter.
3. The method of claim 1, wherein the device includes an air intake
opening for air to enter the device and wherein the filter is
positioned between the air intake opening and the sterilization
chamber whereby substantially all air that enters the sterilization
chamber passes first through the filter.
4. The method of claim 3, wherein the sterilization chamber
includes an air intake baffle to prevent ultraviolet light from
escaping from the sterilization chamber through the air intake
opening and into the room.
5. The method of claim 4, wherein the releasing of the air
including the destroyed bacteria back into the room is through an
air exhaust opening in the device, and wherein the sterilization
chamber includes an air exhaust baffle to prevent ultraviolet light
from escaping from the sterilization chamber through the air
exhaust opening and into the room.
6. The method of claim 5, wherein at least one of the intake
channel and exhaust channel is coated with an ultraviolet
light-absorptive coating to absorb ultraviolet light incident
thereon.
7. The method of claim 1, wherein the sterilization chamber has an
upstream side where the air enters the sterilization chamber and
downstream side opposite the upstream side, the upstream side and
downstream side being configured such that air enters the
sterilization chamber from the upstream side and passes the
ultraviolet light bulb a first time, reflects off the downstream
side and passes the ultraviolet light bulb a second time, and exits
the sterilization chamber.
8. The method of claim 7, wherein the device includes a housing
having a top surface and wherein the ultraviolet light bulbs are
positioned within the housing below the top surface, and the
downstream side includes a downstream surface extending from the
housing top surface downward and toward the ultraviolet light
bulbs, wherein the downstream surface and housing top surface
define a recess to receive air flowing through the sterilization
chamber and to reflect the air back toward the ultraviolet light
bulbs.
9. The method of claim 1, wherein the air is drawn through the
device at an air flow rate that is calculated to produce at least
ten air exchanges per hour in the room.
10. An apparatus for destroying airborne tuberculosis bacteria,
comprising a housing; an air intake opening in the housing for air
to pass into the housing; an air exhaust opening in the housing for
air to pass from the housing; a sterilization chamber in the
housing and-in communication with the air intake opening and air
exhaust opening, the sterilization chamber including at least one
ultraviolet light bulb for irradiating the sterilization chamber
with germicidal ultraviolet light; the sterilization chamber being
configured such that the air passes the ultraviolet light bulb
twice; a blower in communication with the air exhaust opening to
draw air into the air intake opening, through the sterilization
chamber, and out the air exhaust opening.
11. The apparatus of claim 10, further comprising an air intake
baffle between the air intake opening and the sterilization chamber
to prevent ultraviolet light from passing from the sterilization
chamber and out the air intake opening.
12. The apparatus of claim 11, further comprising an air exhaust
baffle between the air exhaust opening and the sterilization
chamber to prevent ultraviolet light from passing from the
sterilization chamber and out the air exhaust opening.
13. The apparatus of claim 10, wherein the housing has an upper
side, a lower side, a front side and a back side, and the air
intake opening and the air exhaust opening are on different said
sides.
14. The apparatus of claim 10, wherein the air intake opening and
the air exhaust opening are on opposite sides.
15. The apparatus of claim 10, further comprising a door in the
housing to access the ultraviolet light bulb.
16. The apparatus of claim 10, wherein the sterilization chamber
includes an upstream side from which the air enters and a
downstream side opposite the upstream side, the downstream side
defining a recess to receive air flowing through the sterilization
chamber and to reflect such air back toward the ultraviolet light
bulb.
17. The apparatus of claim 16, wherein the upstream side is
positioned between the air intake opening and the sterilization
chamber such that air flowing into the device flows around the
upstream side and into the sterilization chamber.
18. The apparatus of claim 17, wherein the upstream side includes a
recess toward the air intake opening to receive air flowing into
the device.
19. The apparatus of claim 10, wherein the apparatus does not
include any filter to trap particulates smaller than 10 microns in
diameter.
20. The apparatus of claim 19, wherein the apparatus includes
filter between the air intake opening and the sterilization chamber
to trap particulates larger than 10 microns in diameter.
Description
[0001] This is a continuation of application Ser. No. 08/087,178
filed Jul. 2, 1993, which is a continuation-in-part of application
Ser. No. 07/960,085 filed Oct. 9, 1992.
FIELD OF THE INVENTION
[0002] The present invention relates to the field of germicidal
systems employing bacteria-destroying ultraviolet lights. In
particular, the present invention relates to a system for producing
an air flow through a baffled ultraviolet sterilization chamber
mounted behind a wall or ceiling, wherein the ultraviolet light
intensity, the air residency time, and the air exchange rate for
the air volume in a given space, are such that a percentage of
tuberculosis bacteria are destroyed that effectively prevents
transmission of such disease by airborne sputum.
BACKGROUND OF THE INVENTION
[0003] Tuberculosis is the most common cause of death from
infectious disease in the world today. It infects millions of
people each year and causes hundreds of thousands of fatalities.
The disease is particularly prevalent in less-industrialized
countries where high population densities, poor sanitary conditions
and a high percentage of individuals in poor health contribute to
the spread of infectious diseases.
[0004] After a long period of declining rates of tuberculosis
infection in the United Sates, it is believed that the infection
rate is now increasing. The increasing rate is apparently due to a
combination of factors. One factor is undoubtedly increased
immigration from parts of the world with high rates of infection.
For example, in the United States the case rate of tuberculosis per
100,000 population was 9.3 in 1985, resulting in over 22,000 cases
and over 1,200 deaths. In Southeast Asia, both the case rate and
the death rate are believed to be many times that, and immigrants
from that part of the world now constitute 3 to 5% of new cases in
the United States.
[0005] Another factor related to increased rates of tuberculosis
infection appears to be the use of living quarters with high
population densities and less-than-ideal sanitary conditions for
persons in ill health who are susceptible to the disease. Such
conditions are commonly found in shelters for the homeless, prisons
and some nursing homes. Another important factor in the increased
rate of infection is infections among patients with Acquired Immune
Deficiency Syndrome (AIDS) and intravenous drug users.
[0006] Another reason for the recent increased incidence of
tuberculosis is probably the failure of many medical professionals
to diagnose and treat the disease early and properly. The relative
rareness of the disease in the United States since the early
epidemics resulted in an entire generation of health care workers
without much experience in the disease. Further, diagnosing the
disease is not always easy, for the symptoms are similar to the
symptoms of many other disorders. Therefore, the disease is often
misdiagnosed and mistreated, and the degree of infectiousness of
the disease is underappreciated.
[0007] Even after it is recognized that a set of symptoms may
indicate tuberculosis, the tests for the disease are somewhat
imprecise and tend to require judgment by an experienced
professional. For example, one diagnostic tool is chest x-rays
which typically show apical-posterior segment cavitary changes in
tuberculosis infected patients. However, in elderly
individuals--who comprise a relatively large proportion of
tuberculosis patients--lobar or patchy lower-zone shadows may
simulate bacterial or aspiration pneumonia. Also, x-rays in the
elderly may mislead the physician by showing a solitary pulmonary
nodule or a pleural effusion. Another important tuberculosis test
is the tuberculosis skin test, but a major disadvantage to the
tuberculosis skin test is that it generates a high number of both
false-positive and false-negative results. The most precise test is
microscopic examination of a sputum sample, but this test may
require the use of at least three separate samples of sufficient
volume, which may require gastric aspiration or bronchoscopy in
patients with low sputum production.
[0008] The normal body reaction to infection by tuberculosis
bacteria is to build a fibrous wall around each bacterium.
Initially, a person may be unaware of any infection, but over a
period of months or even years the infection produces inflammation
and eventually destruction of tissue. The manifestations as the
disease progresses generally include cough, fever, night sweats,
hemoptysis, chest pain, weight loss and malaise. The usual
treatment for tuberculosis is administration of drugs over a period
of many months such as isoniazid, rifampin and pyrazinamide and
ethambutol. Persons recently infected but with no active disease
are usually given isoniazid preventive therapy, particularly if
they have other risks such as malnutrition, gastrectomy, diabetes
mellitus, pneumoconiosis, malignancy or if for some reason they
have immunosuppression such as from corticosteroid therapy, renal
impairment or HIV infection. In short, tuberculosis in a normal
healthy patient is typically a disease that is curable by drugs,
although the drug therapy is quite prolonged. A serious
concern--and yet another reason for the recent increase in
tuberculosis--is the development of drug-resistant tuberculosis. It
is estimated that at least 5% of new cases are resistant to the
usual drug therapy, and that the percentage in some areas of the
United States is as high as 20%. While non-drug-resistant
tuberculosis is typically 99% curable in patients with normal
immune responses, drug-resistant tuberculosis is only about 50-60%
curable. A related concern is drug therapy on nondrug-resistant
tuberculosis for patients who are intolerant of the drugs. In those
cases, drug therapy is complicated because the drug is effective
against the infection but has serious adverse effects on the
patient such as hepatitis or serious rashes.
[0009] Another concern is raised by the increasing incidence of
non-tuberculosis mycobacterial pulmonary infections. Many such
infections produce symptoms similar to those of tuberculosis
infections, but may be more difficult to identify and treat.
Moreover, they may be transmitted through the same means as
tuberculosis and tend to infect the same types of susceptible
individuals.
[0010] The transmission of the tuberculosis bacteria is
accomplished almost exclusively by infected individuals
expectorating microdroplets of bacteria-containing sputum by
coughing or sneezing. These microdroplets are suspended in the air
and are inhaled by other individuals in the vicinity. The bacteria
typically lodges in the lower lung where it proliferates, and may
be disseminated to other organs as well. The microdroplets of
sputum which contain the bacteria may be very small--on the order
of 0.01 microns. In fact, it appears that the smallest droplets are
the most effective in communicating the disease since the smallest
droplets stay airborne indefinitely and are easily inhaled to the
lower lung where they are not readily removed. Studies have shown
that aerosol droplets on the order of 1-5 microns are highly
effective vehicles for transmitting the disease.
[0011] One controversial approach to combatting the disease has
been the use of vaccines. However, the efficacy of tuberculosis
vaccines is debatable. Even the trials which seemed to show some
efficacy have shown less efficacy among adults than among infants
and children. An additional objection to widespread vaccinations is
that by inducing tuberculin reactivity in the population they would
confound the detection and measurement of infections through the
use of skin tests, since skin tests in vaccinated individuals would
presumably result in a false-positive. This would severely curtail
the practice of preventive drug therapy among infected patients who
have not yet developed outward symptoms.
[0012] The airborne aspect of the disease has led toward systems
for preventing the transmission of the disease which focus on
filtration and sterilizing devices. One approach is the use of
masks. Simple surgical masks are thought to be insufficient in view
of the very small size of the sputum microdroplets which are
effective in communicating the bacteria. Instead, disposable
particulate respirators are recommended. The use of masks is
fraught with practical difficulties; they are physically
uncomfortable, they impair breathing (which is already impaired for
many patients), and they disrupt speaking. To be effective at all,
it would probably be necessary for the masks to be worn not just by
the patients, but also by noninfected individuals. In view of the
long distances that airborne microdroplets containing viable
bacteria can travel, it would be necessary for the masks to be worn
by noninfected individuals throughout the general vicinity of a
patient and not just those in the immediate presence of a patient.
Moreover, it is not known for certain whether the use of masks
would actually be effective even if the practical problems were
tolerated or overcome.
[0013] Another preventive measure which relies on the airborne
aspect of the bacteria is the use of modified ventilation systems.
It is currently recommended that facilities used for tuberculosis
patients undergo certain minimum air exchange rates, under the
theory that dilution of infectious air with clean air will reduce
the concentration of bacteria and hence the likelihood of
transmission of the disease. While this approach is theoretically
sound, it is problematic in implementation. Modern buildings are
normally designed with fixed ventilation systems which are not
easily modified to produce the requisite air exchange rate. Even if
they are suitably modified, they may be rendered ineffective by an
open door or by shifting air-flow patterns. A high air exchange
rate also increases cooling and heating costs. Finally, there is
the issue of the ultimate disposition of the contaminated air that
is removed, and whether it is appropriate to simply release it
outside the facility.
[0014] Another approach to reducing the transmission of the disease
is the use of high-efficiency filtration systems. For such a system
to be effective, however, it must employ a very dense filter to
trap very small particles. This entails a powerful lan, high energy
usage, loud noise, and meticulous installation and maintenance.
There is also concern that the filters and the rest of the air-flow
path may themselves become sites of bacteria colonization.
[0015] Yet another approach to reducing the transmission of the
tuberculosis bacterial employs ultraviolet light as a germicide. It
was discovered some time ago that airborne bacteria are susceptible
to ultraviolet light in wavelengths of about 254 nm. Wells S. F.,
On Air-Borne Infection: II-Droplets and Droplet Nuclei, Am. J. Hyg.
1934 20: 611-8; Wells W. F., Fair G. M., Viability of E. Coli
Exposed to Ultraviolet Radiation in Air, Science 1935; 82:280-1.
That finding led to the development of systems using ultraviolet
light as a germicide against airborne bacteria such as measles and
tuberculosis. However, interest in such systems diminished when
later investigators were unable to obtain the desired efficacy.
Also contributing to the diminished interest in such systems was
the recognition that ultraviolet lights produced harmful ozone and
also produced skin and eye irritation. With the development of
streptomycin and chemotherapy for tuberculosis treatment, the
belief became prevalent that tuberculosis would be eradicated and
that preventive systems would be unnecessary.
[0016] The systems that were developed using ultraviolet light as a
germicide against tuberculosis were imprecise, marginally
effective, and perhaps dangerous. The most common system simply
employed ultraviolet lights mounted on or suspended from a wall or
ceiling of a room. For example, a system employing lights suspended
from the ceiling is described in some detail in Riley, R. Z.,
Knight, M. and Middlebrook, G., Ultraviolet Susceptibility of BCG
and Virulor Tubercle Bacilli, Am. Rev. of Resp. Dis., 1976,
113:413. The problems in such a system are numerous. It relies
completely on normal air circulation in the room where it is
installed to bring the bacteria within range of the ultraviolet
light. The normal circulation in a room may be too low for the
ultraviolet light to destroy a necessary proportion of bacteria, or
the normal circulation may be high enough but of a pattern that
does not bring the airflow past the ultraviolet light. Moreover,
there is no single test to determine whether the circulation rate
and patterns are adequate or not for a given installation. Further,
such systems quickly become contaminated by dust on the light bulbs
which diminishes their effectiveness. From a safety standpoint, one
of the greatest concerns is that the simple light shields used with
such systems allow light to be reflected off the walls and ceiling
and onto the skin and eyes of the occupants. The degree of danger
associated with the indirect ultraviolet irradiation is disputed,
but there is undoubtedly at least some danger if the period of
exposure is prolonged. In explaining the necessary safety
precautions, Riley, R. L. and Nordell, E. A., Clearing the Air, The
Theory and Application of Ultraviolet Air Disinfection, Am. Rev.
Respir. Dis. 1989 139:1286, stated:
[0017] Does germicide UV cause inflammation of skin and eyes? It
can, but the standard set by the National Institute of Occupational
Safety and Health (NIOSH) is very conservative. Overhead
installations must be inspected for `hot spots` (greater than 0.2
uW/cm.sup.2) with a sensitive UV meter. Installers should
anticipate readjusting fixture height up or down based on meter
readings. Baffles designed to prevent direct eye contact will also
need adjustment after the initial installation. Excessively
reflective surfaces about fixtures may contribute to excess
radiation, but this can be reduced with nonreflective paint or by
spraying the surface with stove black. If the intensity of UV does
not exceed 0.2 uW/cm.sup.2, the likelihood of skin or eye
irritation is minimal during an 8-h exposure. Persons with
especially sensitive skin, with systemic lupus erythematous, for
example, may need to avoid exposure or take measures to protect
their skin.
[0018] This illustrates some of the difficulties and dangers of
employing ultraviolet lights behind a simple light shield; the
light may generate dangerous and unpredictable "hot spots", it is
not appropriate for those with sensitive skin or eyes, and it
requires careful consideration of the placement and the orientation
and reflectivity of the surrounding surfaces. Finally, even if all
those precautions are observed, the quote only indicates that skin
and eye irritation is "minimal" rather than nonexistent and only
for exposure periods of 8 hours. Of course, for the system to be
effective against transmission of airborne disease in, for example,
a patient room, it would have to operate continuously and not just
for 8 hour periods. The article goes on to acknowledge that:
[0019] UV or disinfection that is inappropriately applied, poorly
planned, or carelessly used may be ineffective, dangerous, and
falsely reassuring. The guidelines and precautions listed above are
not intended to enable a would-be user of UV to plan, purchase,
install, or check the adequacy of a UV installation. Detailed
instructions for UV installers have been published. However, there
is currently little commercial interest in UV for air disinfection
and, therefore, little expert guidance for comprehensive planning
and installation. Renewed consumer interest may stimulate the UV
industry to correct this deficiency.
[0020] Notwithstanding the uncertainly expressed in the Riley and
Nordell article regarding the dangers of ultraviolet radiation,
that article is actually more cognizant of those dangers than much
of the other literature on the subject. For example, the article by
Riley, Knight and Middlebrook, supra, does not even mention the
dangers to the skin and eyes of ultraviolet radiation, or any
precautions that should be taken to minimize those dangers.
[0021] There are number of ultraviolet germicidal systems that have
been patented, but as in the case of the scientific literature
mentioned above, those patents teach little about the dangers of
ultraviolet radiation and how to effectively minimize the dangers,
or how to position and operate the devices to achieve the requisite
bacterial kill rate to prevent transmission of disease.
[0022] For example, U.S. Pat. No. 3,975,790 by Patterson is for an
ultraviolet lamp fixture used in combination with a conventional
commercial vacuum cleaner, and U.S. Pat. No. 4,087,925 by Bienek is
for a sterilizing hand dryer, in which ultraviolet lights are
positioned within the housing of a blower that is used to dry wet
hands, where the blower is of the type commonly used in commercial
restrooms. The devices of Patterson and Bienek seem to include
little or nothing for light baffling to prevent leakage of
allowable light to outside the housing, and the patents teach
nothing about optimal flow rates, air-exchange rates or other
information for the effective use of the machines. The devices are
obviously intended as general, and only partially effective,
sterilizing tools rather than as comprehensive and predictably
effective systems.
[0023] Another patent, U.S. Pat. No. 4,210,429 by Golstein, employs
a "squirrel-cage" type blower which draws air into a housing
through a air intake filter, through the blower, and through a
sterilization chamber containing ultraviolet lights. The air leaves
the sterilization chamber, passes through a second filter and a
charcoal filter and finally exits through an outlet. The
specification indicates that the purpose of the device is to remove
"pollens, lung damaging dust, smoke, bacteria and any one of a
number of other irritants and micro-organisms" and that it does so
for "particles down to 0.3 microns in size with an efficiency of
99.9%". The device is characterized as an "air purifier" rather
than as a germicidal device; the use of three distinct filters
including a very fine filter for removing extremely small
particles, a charcoal filter for removing odors and a pre-filter
for removing particles, is distinguishable in design and function
from the present invention. This extensive filtration would require
a high-capacity blower to achieve any effective air exchange rate.
The device is not specifically designed for destroying the
tuberculosis bacteria or any other specific bacteria, although it
would obviously be effective in doing so to some extent. Therefore,
the patent teaches nothing about the use of the device for that
purpose or the optimal flow rates or positioning of the device for
that purpose.
[0024] U.S. Pat. No. 5,074,894 by Nelson is for a hospital room to
quarantine patients with tuberculosis or other respiratory diseases
caused by airborne pathogens. Although one embodiment of the system
includes an air circulation circuit with ultraviolet lights, the
patent is directed primarily toward negative pressure and filtering
aspects utilizing high-efficiency particulate air filters.
[0025] Other patents describing the use of ultraviolet light as a
germicide against airborne bacteria include, U.S. Pat. Nos.
4,448,750 by Fuesting, 4,896,042 by Humphreys, 4,990,311 by Hirai
and 4,047,072 by Wertz, 4,990,313 by Pacosz, 3,072,978 by Minto,
4,227,446 by Sore, 3,347,0235 by Wiley, 4,786,812 by Humphreys,
4,990,311 by Hirai, 4,931,654 by Horng, 4,806,768 by Keutenedjian,
4,750,917 by Fugii, 3,757,495 by Sievers, 3,750,370 by Brauss,
3,745,750 by Arff, 3,744,216 by Halloran, 3,674,421 by Decupper,
3,576,593 by Cicirello, and 5,185,015 by Searle. Patents directed
toward the use of ultraviolet light as a germicide against bacteria
in water or other liquids include U.S. Pat. Nos. 4,400,270 by
Hillman, 4,482,809 by Maarschalkerweerk, 5,102,450 by Stanley and
5,124,131 by Wekhof.
SUMMARY OF THE INVENTION
[0026] The present invention is an apparatus and process for
destroying airborne pathogenic bacteria such as the tuberculosis
bacteria. Ultraviolet lights of a sufficient intensity are
positioned within a sterilization chamber where they irradiate an
air stream containing the bacteria, typically in the form of
suspended microdroplets of sputum. The sterilization chamber has an
exit and an entrance, and a blower is positioned preferably at the
exit to draw air into the entrance and through the sterilization
chamber and out the exit. The air circulates behind an intake
baffle and into the sterilization chamber having a set of
ultraviolet lights. An outlet baffle at the opposite side of the
sterilization chamber bounces the air that passes the ultraviolet
lights back over the ultraviolet lights a second time, and around
the outlet baffle to the fan. The fan then expels the sterilized
air back into the room. The air passing through the sterilization
chamber is virtually completely sterilized of viable tuberculosis
bacteria by the chosen dosimetry of the system, which is achieved
by appropriately sizing the sterilization chamber employing
ultraviolet lights of the correct intensity, and utilizing the
right air flow rate through the blower. The apparatus is configured
to fit behind a wall in a room, or preferably, above a suspended
ceiling. Air is drawn by a fan from the room into an intake duct
and into the apparatus.
[0027] The sterilization chamber includes a filter on the intake
side to filter out large particles such as dust, in order to
minimize the contamination of the ultraviolet light bulbs. The
filter is deliberately designed not to intercept small particles
such as microdroplets, since the filter could then become a
bacteria colony. The use of a low density filter also minimizes the
resistance to air flow, thereby allowing the use of a smaller, more
efficient and quieter blower. With the exception of this intake
filter for removing large particulates, the apparatus preferably
does not include any devices that would intercept and retain
microdroplets or other small particles in a way that resists the
air flow and poses the possibility of becoming a bacteria
colonization site; the small particulates and microdroplets with
destroyed bacteria simply pass through the apparatus and are
expelled back into the environment.
[0028] Both the air intake and exhaust to the sterilization chamber
are baffled so that ultraviolet light must reflect off multiple
surfaces before exiting the sterilization chamber. The interior
surfaces of the baffles may be light-absorptive to minimize their
reflectivity and further lessen the possibility of ultraviolet
light leaking from the sterilization chamber into the
environment.
[0029] The apparatus is used in a space having a volume of air that
results in an air exchange rate of preferably 12-15 air exchanges
per hour. At that air exchange rate, it has been determined that a
sufficient volume of air will circulate through the apparatus and
will prevent any air stagnation in the room, that a high enough
percentage of tuberculosis bacteria will be destroyed before they
are inhaled by persons in the room to prevent transmission of the
disease.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a pictorial cutaway view of the present
invention.
[0031] FIG. 2 is a side sectional view of the present invention,
taken along line 2-2 of FIG. 1, installed in a suspended
ceiling.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] A pictorial view of a preferred embodiment of the invention
is shown in FIG. 1. The principal elements of the invention 10
include an exterior housing 40 having an air intake duct 42 and an
air discharge duct 44, a squirrel-cage type blower 120 and set of
ultraviolet lights 150 in a sterilization chamber 180 within the
housing 40. The air intake duct 42 is preferably positioned at one
end 46 of the housing and the air discharge duct 44 is positioned
at the opposite end 47 of the housing 40.
[0033] As better shown in the sectional view of FIG. 2, the air
intake duct 42 has positioned within it a filter 60 which
substantially fills the intake duct 42 so that all air drawn
through the air intake duct 42 must pass through the filter 60. The
filter 60 is preferably not a high-density filter, but is instead
designed to intercept and retain only fairly large particulates
such as dust. The purpose of the filter 60 is not to allow the
apparatus 10 to purify the air, but is merely to intercept dust
over 10 microns in size that would otherwise contaminate the
ultraviolet light bulbs 150. In a preferred embodiment, the filter
is model no. DP1-40, available from Airguard Industries located in
Louisville, Ky. The filter 60 is retained in the air intake duct 42
by means of clips, brackets or any other suitable retention means
(not shown) that allow easy removal and replacement of the filter
60.
[0034] It is notable that in the preferred embodiment, there is no
filter at all in the air discharge duct 44 or elsewhere downstream
from the sterilization chamber. Therefore, the only filter in the
preferred embodiment is the large particulate filter 60 positioned
in the air intake duct 42. The apparatus 10 is designed to allow
small particulates, including microdroplets of sputum containing
bacteria that are destroyed by the ultraviolet lights as described
below, to be expelled back into the environment. As a result, the
apparatus does not have a site that traps and allows the
colonization of bacteria, which would require frequent cleaning or
sterilization. In addition, there is very little resistance to air
flow, thereby allowing the use of a relatively small, low-energy
and quiet motor and blower system, as further described below.
[0035] In this respect, the present system is fundamentally
different from prior art devices that are designed to remove dirt,
pollen and other particulates and odor from the air. Those prior
art systems employ dense and multiple filters and noisy high-energy
blowers to indiscriminately remove impurities from the air. But
they are not specifically for the purpose of destroying pathogenic
pulmonary bacteria such as tuberculosis and their efficiency in
doing so is undocumented and questionable. In contrast, the present
system is specifically designed for destroying bacteria such as the
tuberculosis bacteria, and is highly effective in accomplishing
that using a relatively small, energy efficient, quiet apparatus,
but the present system makes no attempt at all to remove impurities
from the air. Even the bacteria itself is released back to the
environment once it is killed by the apparatus.
[0036] The air discharge duct 44 is preferably positioned remotely
from the air intake duct 42, so that the exhausted air circulates
into the environment rather than being immediately drawn back into
the apparatus 10. In the embodiment shown in FIGS. 1 and 2, the
positioning of the ducts 42 and 44 on opposite ends of the housing
produces a circulatory effect through the environment of the
apparatus 10 by drawing air into the apparatus 10 through the air
intake duct 42 and expelling air from the apparatus 10 through the
air discharge duct 44, roughly in the direction of the arrows shown
in FIG. 2. The air discharge duct 44 may be covered with a grill
(not shown) to prevent the introduction of hands or objects into
the air discharge duct 44 and to diffuse the air stream exhausted
from there. A door 183 is positioned in the bottom of the housing
40 as shown in FIG. 2 and is attached to the housing 40 by a hinge
185 or other suitable attachment means. The door is positioned to
allow ready access to the ultraviolet lights 150 and to the filter
60 to allow them to be changed or cleaned.
[0037] The sterilization chamber 180 is baffled on the upstream
side by an intake baffle 182, and on the downstream side by a pair
of exhaust baffles 184 and 187, to prevent ultraviolet light from
leaking from the sterilization chamber 180 out the air intake duct
42 or air discharge duct 44 and into the environment where it could
damage the skin and eyes of patients and other persons. The baffles
also improve the circulation of the air over the ultraviolet bulbs
in the manner described below. The intake baffle 182 in the
preferred embodiment is an S-shaped element fabricated from sheet
metal or other appropriate material that is not degraded by
ultraviolet light. The lower portion of the intake baffle 182 is
curved away from the air intake duct 42 to receive the incoming
air, while the upper portion of the intake baffle 182 is curved
toward the sterilization chamber 180 to allow the incoming air to
flow smoothly over the top of the intake baffle 182 and into the
sterilization chamber 180. The intake-baffle 182 may be attached to
the housing 40 at the bottom of the intake baffle 182 or at the
ends.
[0038] The exhaust baffles 184 and 187 form a channel therebetween
for the air to leave the sterilization chamber 180, as best shown
in the sectional view of FIG. 2. Both exhaust baffles 184 and 187
are curved with the inner side of the curve away from the
sterilization chamber 180. The air passes under the lower edge of
the upper exhaust baffle 184, through the channel defined by the
upper baffle 184 and 187, and over the upper edge of the lower
exhaust baffle 187.
[0039] The upper exhaust baffle 184 may be attached to the housing
40 at the top of the upper exhaust baffle 184 or at the ends. The
lower exhaust baffle 187 may be attached to the housing 40 at the
bottom of the lower exhaust baffle 187 or at the ends.
[0040] It can be appreciated that for any ultraviolet light to
escape from the sterilization chamber 180 through the air discharge
duct 44, it must reflect off the walls of the sterilization chamber
180, reflect through the channel defined by the upper and lower
exhaust baffles 184 and 187, and then through the blower 120 and
out the air discharge duct 44. For any ultraviolet light to escape
through the air intake duct 42, it must reflect off the walls of
the sterilization chamber 180, into the space between the air
intake duct 42 and the intake baffle 182, through the air intake
filter 60 and through the air intake duct 42. The possibility of
light escaping can be further reduced by applying an absorptive
coating or paint to the interior surfaces of the baffles 182, 184
and 187 and the other interior surfaces of the housing 40.
[0041] Although the baffling described above to prevent ultraviolet
light from escaping presents a circuitous route for the passage of
air from the air intake duct 42 through the sterilization chamber
180 and out the air discharge duct 44, the baffles are still
designed to minimize the resistance to air flow. Thus, as shown by
the arrows in FIG. 2, the air can flow reasonably smoothly with
limited turbulence loses, thereby allowing a small, quiet and
efficient blower system.
[0042] An important aspect of the embodiment shown in FIGS. 1 and 2
is that the baffles 182 and 184 and sterilization chamber 180 are
configured such that the air passes the ultraviolet lights twice.
As shown by the arrows of FIG. 2, the air passes the ultraviolet
lights a first time immediately after it passes over the top of the
air intake baffle 182 and into the sterilization chamber. The air
pathway is blocked on the opposite side of the sterilization
chamber by the air exhaust baffle 184. The inclined and curved
surface of the air exhaust baffle, together with the top wall of
the housing 40, define a space 186 to receive the air after it
passes the ultraviolet light a first time. The air then reflects
off the air exhaust baffle 184 and out of the space 186 and back
toward the ultraviolet lights for a second pass. The air is then
drawn out of the sterilization chamber 180 by passing under the
exhaust baffle 184 and into the blower 120.
[0043] The blower 120 in the preferred embodiment is of the
"squirrel-cage" type. The blower 120 draws air through its ends and
propels the air out the middle and into the exhaust duct 44. The
exact size of the blower and the motor for the blower depend on the
desired use of the machine and the size of the environment in which
it will be used, as further discussed below. The motor is
preferably of the normal alternating current type and is in
communication with the electrical system (not shown) of the
apparatus, which also powers the ballasts for the ultraviolet
lights 152. The electrical system is ordinary, and the details of
it will be apparent to those skilled in the wiring of lights and
motors, and it is not further described herein.
[0044] The apparatus 10 is preferably positioned in the suspended
ceiling 191 of a patient room as shown in a preferred arrangement
in FIG. 2. Cutouts in the ceiling 191 are provided for the air
intake duct 42, air discharge duct 44 and access door 183. The
microdroplets from the patient are expectorated from the patient
into the surrounding air where they are suspended. The air currents
produced by the apparatus 10 draws air into the apparatus 10 from
intake duct 42. The filter 60 traps large dust particles, but
allows small particles to pass including the micro droplets of
small bacteria-containing sputum. The air with the suspended
microdroplets passes through the sterilization chamber where the
bacteria are destroyed by passing twice over the ultraviolet
lights, and the air along with the suspended microdroplets with the
then-killed bacteria are expelled from the apparatus 10 back into
the room through the air discharge duct 44. Because the air
discharge duct 44 is preferably positioned at one end 46, of the
apparatus 10 while the air intake duct 42 is positioned at the
other end 47 of the apparatus, the air being drawn into the air
intake duct 42 and expelled from the air discharge duct 44 produces
a circulatory effect through the room which increases the flow of
new unsterilized air into the apparatus. This circulatory effect
also helps prevent the air from short-circuiting the circulation
pattern by leaving the apparatus 10 through the air discharge duct
44 and immediately re-entering the apparatus 10 through the air
intake duct 42 without passing through the room.
[0045] It has been determined experimentally that transmission of
the tuberculosis bacteria from an infected patient to an uninfected
person can be effectively prevented by ensuring that there are
approximately 10 to 15 air changes per hour in the patient room
using the apparatus and positioning described above. The phrase "10
to 15 air changes per hour" means a circulatory effect through the
apparatus in which the total volume of air through the apparatus
per hour equals the air volume of the room multiplied times a
number between 10 and 15, inclusive. For example, one air change
per hour in a 1,000 cubic foot room would require an apparatus
through which 1,000 cubic feet of air pass per hour. Therefore, in
a patient room having dimensions of 10 by 10 by 10 feet for a total
volume of 1,000 cubic feet, or other dimensions for a total volume
of 1,000 cubic feet, the apparatus should be capable of circulating
through it at the rate of 10,000 to 15,000 cubic feet of air per
hour.
[0046] The exact dimensions of the apparatus to achieve such a flow
rate in a preferred embodiment include a housing 40 having a length
of about 48 inches, a height of about 15.5 inches, and a depth of
about 36 inches. The air intake duct 42 is roughly 6 inches by 24
inches and the air discharge duct 44 is roughly 6 inches by 18
inches. The opening between the top of the air intake baffle 182
and the housing 40 is about 4 inches, and the opening between the
bottom of the air exhaust baffle 184 and the housing 40 is about 4
inches. The motor is a 115 volt, 1,725 rpm motor, and the blower
120 includes 4 by 9 inch blower wheels. The ultraviolet lights 152
are model D-36-3 by American U.V. Co.
* * * * *