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Publication numberUS3511162 A
Publication typeGrant
Publication dateMay 12, 1970
Filing dateFeb 20, 1969
Priority dateFeb 20, 1969
Also published asCA919486A, CA919486A1, DE2007652A1
Publication numberUS 3511162 A, US 3511162A, US-A-3511162, US3511162 A, US3511162A
InventorsAndrew Truhan
Original AssigneeJohnson & Johnson
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Apparatus and method for isolating a patient zone
US 3511162 A
Abstract  available in
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

May 12., 1970 A. TRUHAN 3,511,162

APPARATUS AND METHOD FOR ISOLATING A PATIENT ZONE Filed Feb. 20, 1969 3 Sheets-Sheet 1 gaffer/a 000/ INVENTOR //V0/PEW THA /41v 77m 27 ,Jecmds ATTORNEY y 12, 0 A. TRUHAN 3,511,162

APPARATUS AND METHOD FOR ISOLATING A PATIENT ZONE Filed Feb. 20, 1969 3 Sheets-Sheet 2 once one.

INVENTOR ,7 ATTORNEY A. TRUHAN May 12., 1970 APPARATUS AND METHOD FOR ISOLATING A PATIENT ZONE 3 Sheets-Sheet 3 Filed Feb. 20, 1969 INVENTOR Ame/a5 7'fiu/M/v I BY 1 ATTORNEY United States Patent "cc 3,511,162 APPARATUS AND METHOD FOR ISOLATIN-G A PATIENT ZONE Andrew Truhan, Somerset, N.J., assignor to Johnson & Johnson, a corporation of New Jersey Continuation-impart of application Ser. No. 671,625, Sept. 29, 1967. This application Feb. 20, 1969, Ser.

Int. Cl. F24f 9/00 US. CI. 98-36 10 Claims ABSTRACT OF THE DISCLOSURE An apparatus and method for providing a controlled environment in a localized patient zone. An air distributing structure, having at least two opposed enclosed sides and two opposed open sides for surrounding the patient zone, is equipped with an overhead inlet plenum and an exhaust duct adjacent the bottom of the zone. The periphery of the plenum along the open sides of the zone is provided with structure for forming a high velocity air curtain between the plenum and the exhaust duct to effect the complete enclosure of the zone. An air treating apparatus feeds purified air into the plenum and withdraws air from the exhaust duct for recirculation through the system.

BACKGROUND OF THE INVENTION This is a continuation-in-part of my copending appli cation Ser. No. 671,625 filed Sept. 29, 1967.

This invention relates to an apparatus and method for controlling the environment in a localized zone and, more particularly, to an apparatus and method for effectively isolating a patient zone from the external environment.

Despite the flourishing in recent years of improved aseptic techniques and antibiotic drugs, hospital-acquired infections continue to harass the most eificiently operated hospitals. These infections are particularly threatening to severely injured or debilitated patients and those whose resistance is lowered by disease or the action of immunosuppresive drugs. Patients with extensive burns, premature infants, and those who have undergone organ transplants are examples of people who are seriously threatened by pathogenic microorganisms. Yet, at the same time, patients are brought for treatment in the same hospitals for infections in which the most dangerous of pathogens are proliferating.

The need to prevent cross-contamination is obvious and has led to well-known methods of prevention, such as antiseptic scrubs, sterilized equipment and clothing, and meticulous housekeeping methods. Yet one pathway remains for pathogenic microorganisms to travelthe air currents within hospital rooms and corridors.

The danger of airborne contaminants has been recognized for decades and previous attempts to reduce infection rates by purifying hospital air and/ or directing its flow have shown promising results.

All of the known devices designed to isolate a patient zone from the environment have been objectionable for one or more of the following and other reasons: the adverse efiect of the patients morale occasioned by total confinement; the high cost and complexity of rebuilding or modifying an existing room construction; the inaccessibility of the patient to the hospital attendants; and the cost and difficulty of training personnel to operate the systems.

The present invention was designed to overcome all of the above-mentioned objections and, yet, to provide an extremely effective and simply constructed isolation unit.

3,511,162 Patented May 12, 1970 SUMMARY OF THE INVENTION The present invention provides a portable unit for protecting vulnerable patients from airborne bacterial contamination by utilizing a curtain of high velocity, purified air to isolate the patient, yet at the same time permitting easy access to the patient for hospital personnel. The unit is preferably designed to house a standard hospital bed and to be assembled and disassembed easily, so that it can be relocated within the hospital wherever it is needed. In addition to protecting the patient in the bed where it is installed, the unit also serves to reduce bacterial contamination in the immediate environment by capturing and filtering air within the room where the unit is in operation.

By contrast with earlier developments in patient isolation, the present unit does not physically enclose the patient in a relatively inaccessible covering. Instead, the device enables hospital personnel to approach the bed when necessary, taking up airborne contaminants that are introduced and filtering and/or purifying the air before the air is recirculated. In addition to the advantage to hospital personnel, the protected patient derives the psychological advantage of not feeling confined and cut off from his surroundings. The patient can see and hear visitors without being conscious of the air curtain that protects him and his visitors.

The objects and advantages of the invention are accomplished by providing a structure that isolates the patient zone with controlled air flow patterns produced by the inductive effect of symmetrically positioned high velocity air curtains. In a preferred embodiment, a unit is constructed with two opposed structural walls and two opposed openings therebetween to form an essentially rectangular patient zone. A perforated plenum overlies the entire patient zone and an exhaust duct is located near the floor and preferably under the patients bed to exhaust downwardly moving air from the enclosure.

The lateral edges of the plenum along the open sides of the zone are also provided with structure for directing curtains of high velocity air across the openings to effectively seal the openings against airborne contaminants and completely enclose the patient zone. The air curtains, because of their unique symmetrical construction, not only enclose the zone but control the flow patterns of the air from the perforated plenum so that the zone is at all times maintained at an extremely low contamination level and is returned to that level within a short time after bacteria have been introduced into the zone.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be particularly described with reference to the following detailed description of the preferred embodiments of the invention when considered together with the attached drawings, in which:

FIG. 1 is a perspective view of a patient isolation unit constructed in accordance with the teachings of this invention;

FIG. 2 is a vertical sectional view taken through the air treating apparatus of FIG. 1;

FIG. 3 is a vertical sectional view through the controlled environmental patient zone of the apparatus of FIG. 1 and showing the air fiow patterns created within the zone;

FIG. 4 is a vertical sectional view through another another embodiment of the controlled environmental patient zone illustrated in a somewhat schematic form and again showing the air flow patterns created within the patient zone; and

FIG. 5 is a graph illustrating the rapid return of the patient zone to a low contamination level after the zone has had bacteria introduced therein.

3 DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the patient isolation unit A comprises a controlled environmental patient zone shown generally at and an integral air treating device shown generally at 11. Air treating device 11 provides the main structural support for the entire unit and houses the air treating equipment that will be later described. It is an object of this invention to provide an apparatus and method for effectively isolating a patient who is confined to a bed 12 from the remainder of the room environment. Isolation unit A is provided with a first end Wall 13, which may also form an external wall for air treating device 11, and with a second end wall 14 which may be formed of Plexiglas or some other suitable transparent material. Second end wall 14 provides a means for completely sealing the foot portion of bed 12 and at the same time supports one end of the isolation unit. Walls 13 and 14 are both angled laterally outwardly from both sides of the isolation unit to provide additional stability to the unit and to delineate the outer extremity of the air flow which will be described h reinbelow. To aid in the description of the unit, when used herein the word longitudinally shall mean in a direction from the head to the foot of the bed and laterally shall mean in a direction across the bed.

An overhead plenum shown generally at 16 and an exhaust duct 17 cooperate to form the air distributing structure necessary to completely enclose the patient zone 10 and to isolate the patient from the external environment. Referring to FIGS. 1 and 3, plenum 16 comprises a top wall 18, two side walls 19 and 20 and two end walls 21 and 22. End wall 22 may conveniently be constructed as a portion of the back panel for air treating device 11 as shown in FIG. 3.

The internal construction of plenum 16 is best illustrated in FIG. 3 wherein a first perforated plate 24 is located intermediate top wall 18 and a second perforated plate 25. A pair of florescent light housings 26 and 27 are supported by plenum 16 and extend the entire length of the patient zone 10 for supplying light within the isolation unit. Outwardly of housings 26 and 27 a pair of air directing structures shown generally at 30 and 31 are secured between the perforated plates 24 and and the side Walls 19 and 20, respectively.

Referring to FIG. 3, air directing structure is constructed with two elongated plates 33 and 34 which are pivotally secured to the underside of plenum 16. A pair of depending brackets 35 and 36 support adjusting screws 37 and 38, respectively, which may be turned to adjust the pivotal location of plates 33 and 34 and the space between the plates. With this construction, it is possible to direct the flow of air from the plenum 18 at any desired angle within certain limits, to adjust the width of the current of air emitting from between the plates, and to regulate the velocity of the air curtain. The air directing structure 31 on the opposite side of plenum 16 is constructed in a manner identical to structure 30 and no further description of this device is deemed necessary. Perforated plates 40 and 41 are also positioned above air directing structures 30 and 31, respectively, to provide an even flow of air from the upper plenum construction into the air directing apparatus.

The function of perforated plates 24, 25, 40 and 41 is to establish an even flow of air under static pressure from the upper plenum chamber into the patient zone 10 so that undesirable turbulance may be avoided.

Exhaust duct 17 is constructed in a generally rectangular configuration with a solid top portion 43 and a solid end portion 44. The sides 45 and 46 of duct 17 are essen tially vertically positioned and are perforated to enable the air to be drawn into the interior of the duct and circulated to the air treating device 11.

The unique air flow patterns and the advantages derived therefrom will be fully discussed below, however,

the air treating device 11 will first be thoroughly described in order that the invention may be more fully understood. Referring to FIG. 2, the essential structural components of air treating device 11 are shown in cross section with an inlet duct 50 shown in communication with exhaust duct 17 and an outlet duct 51 shown in communication with plenum 16.

Air treating device 11 comprises a cabinet made up of double Walled, insulation-filled panels 52 and 53, front and back panels 54 (FIG. 1) and 55, and top and bottom panels 56 and 57, respectively. A refrigeration unit, shown generally at 58, is mounted separate from the main device 11, preferably in a window or other access to outside atmosphere to avoid heating attendant with the operation thereof. Such units are well known in the art and pref rably comprise a device in which the refrigerant liquid is in heat exchange with an inert fluid such, for example, as brine within the unit for transmission to the point to be cooled to thereby avoid a possibility of contamination if the refrigerant lines are ruptured.

A vertical interior wall 59 and a perforate horizontal wall 60 are arranged Within the enclosure defined by the aforedescribed walls and panels to form therein an air purifying chamber 61. A horizontal wall 62 is disposed surjacent the perforate wall 60 and in spaced relationship thereto to define therewith a pre-treatment air chamber 63 has disposed therein a heating coil 64 connected, through a control 65, to a suitable source of electric power (not shown). A temperature sensing device 66, located in chamber 61, is connected to control 65.

A transverse channel 67, formed in conjunction with horizontal wall 62, interconnects air chamber 63 with a return inlet chamber 68. Chamber 68 is, in turn, connected to exhaust duct 17 through return conduit 50 disposed through wall 52 of the device as hereinbefore described. A fan or blower 69 is disposed between the channel 67 and return duct 50 to circulate gas as shown by the arrows in the figure.

A fluid holding tank 70 is located surjacent channel 67 and is in communication therewith through openings 71 and 72. A valve means, illustrated as a movable flapper valve 73, is disposed in channel 67 between opening 71 and opening 72 whereby a portion of the air stream passing through the channel may be bypassed from an air treating zone 74 in the tank 70 and recirculated directly to chamber 63. This valve means provides additional control for the controlled environment device and will be described below.

Arranged in the tank 70 are a heater coil 76 connected to a suitable source of electric power (not shown). A sensing element, which may comprise a thermister 80, is disposed in tank 70 and is connected to the control 78. Coil 76 and sensing element 80 are submerged in a liquid sump 82 formed in tank 70.

A cooling coil 84 connected by flexible conduits 86 to refrigeration apparatus 58, is also submerged in sump 82 to provide cooling for the fluid therein as required. The refrigeration unit is also connected to the control 78 in such a manner that, by suitable adjustment of that control, heat may be added to sump 82 through heating coil 76 or removed therefrom through cooling coil 84 to maintain a desired temperature therein. Devices suitable for achieving such control are standard in the art and, since the device per se does not constitute a portion of this invention, further detailed description thereof is not included herein. As was discussed hereinbefore, refrigeration unit 58 is of the type wherein the cooling fluid transmitted to coil 84 is cooled in heat exchange relationship to the refrigerant in the unit. This is achieved, in the device illustrated, through means of a heat exchanger 88 in which refrigerant, circulated through a refrigerant line 90, and brine, circulated through the cooling line 92 by a pump 94, are passed in heat exchange relationship to one another. An electric pump 96 communicates with a plurality of spray nozzles 98 disposed in air treatment zone 74 and with liquid sump 82, whereby gas humidifying and temperature conditioning liquid is, in part, continuously recirculated.

A significant component of the air treating device is filter 100 which is designed to fill the entire cross sectional area of air purifying chamber 61. Filter 100 is preferably a high efllciency particulate air (HEPA) filter which is designed to remove 99.97 to 99.99% of all particles and bacteria, 0.3 micron in diameter and larger. Smaller particles also are removed by this type of filter, but the amount of removal has not been established. Removal of smaller particles has not been a matter for concern, however, since bacteria range from 0.3 to 30 microns in size and very rarely exist in the air as single unattached cells but usually attached to particles of dust and skin scales considerably larger than themselves. The median diameter particles carrying pathogenic bacteria in the air has been reported to be about 12. microns, with a range of 4 to 24 microns. The organism chiefly responsible for post operative infection is the hemolytic Staphylococcus aureus, which is approximately 0.5 micron in diameter. The use of high efiiciency particulate air filters for the filtration of minute particles is well known in the art and the success of these filters is well documented.

Additional filters may be employed in the air treating device, such as, pre-filters for removing large particles from the air prior to the contact of the air with the HEPA filter and charcoal filters for removing fumes and odors from the air. These filters have not been illustrated in the drawings since they are well known in the air filtration art.

Although the filter system provides virtually total purification of the air, it has been found to be desirable to provide a bank of ultraviolet lamps 101 within air purifying chamber 61. Ultraviolet radiation has been found to be effective in inactivating living microorganisms and is utilized in this system as an additional safeguard. Al though lamps 101 are shown in FIG. 2 in a location above filter 100, the lamps may conveniently be located anywhere within air purifying chamber 61.

The aforedescribed insulated walls help to reduce to a minimum heat transfer between the chamber 61 and the ambient atmosphere. Such insulation may be of any type standard in the art such, for example, as foam polyurethane, glass wool or the like, or may comprise an evacuated area between the double wall construction. Although any form of perforate wall is suitable within the chamber 61, a hardboard wall having A" diameter perforation on, for example, /2" centers, will provide satisfactory uniform air fiow through the chamber.

The heating coils 64, positioned in chamber 63, are conventional electric coils connected to a suitable source of electric current through a thermostat (not shown) whereby the temperature of the coils may be suitably adjusted and maintained to thereby finally adjust the temperature and humidity of the gas stream to the desired value immediately prior to entrance thereof into chamber 61. This final adjustment provides means to closely control the properties of gas flow.

In operation of the device, the temperature regulating controls 65 and 78 are energized and the pump 96 and fan 69 initiate circulation of gas through conduits 50- and 51 and liquid through the gas treating zone 74. Bypassed gas flowing through the gas treating zone 74 is saturated by the liquid spray from the nozzle 98 and is thereby humidified and simultaneously brought to a temperature condition proximate that in the sump 82. The gas stream is then passed through the chamber 63, through the heating coils 64 to finally adjust the temperature and the rela tive humidity of the gas stream to the value desired in the zone 10. By suitably controlling the quantity of gas which is to fiow through the zone 74 to become saturated at the predetermined temperature of the liquid in the sump 82, the relative humidity and the final temperature of the gas after passing the heating coils 64 is critically maintained. The gas stream then flows through the perforate wall 60 and is purified by filtration through the filter and exposure to the ultraviolet radiation from the lamps 101.

The gas, now fully conditioned and purified, flows through outlet duct 51 into the upper chamber of plenum 16. The gas then flows downwardly through perforated plates 24 and 25 and into the patient zone 10 where it is evenly distributed at a relatively low velocity. Simultaneously, air is ejected from the two air directing struc tures 30 and 31 as indicated by the arrows in FIG. 3 to form air curtains along the open sides of patient zone 10. The air is then exhausted from the patient zone through the perforated sides 45 and 46 of the exhaust duct 17 and into inlet duct 50 of the air treating device for recirculation and purification of the air.

Where radiation such as that emitting from ultraviolet lamps 101 is utilized, a certain amount of heat will be added to the gas stream during the cycling thereof. By suitable regulation of the amount of heat added to the air stream by the heating coils 64, however, and by having a substantial volume of gas flowing constantly through the zone, very uniform temperature and humidity conditions may be maintained through the zone. Where the desired humidity and temperature cannot be fully maintained by the steps of saturating and heating the gas stream, valve 73 may be adjusted to permit a predetermined portion of the air flowing in the channel 67 to be recirculated through the heating coils 64. This bypassed, non-rehumidified air, mixing with the gas stream flowing from the gas treating zone 74, provides a further measure of control for the chamber.

From the foregoing description of the preferred embodiment of the present invention, it can be seen that an improved device for maintaining controlled environment in a portable apparatus is provided. Throughout the discussion of this preferred embodiment of the invention the gas employed has been described as air; however, it will be apparent to those skilled in the art that, in a closed cycle device such as that disclosed herein, an inert atmosphere such as nitrogen may be maintained in the zone 10. Further, the gas may comprise a mixture of gases which may be high in oxygen, high in CO high in CO or the like, without departing from the principles of the invention. Further, in addition to injecting water into the gas stream to provide a saturated gas, other liquid treating agents may be employed so that an atmosphere having a bacteriacidal or fungicidal property may be maintained in the zone 10.

It will be further recognized by those skilled in the art that, while specific controls for regulating the temperature of coils 64 or the temperature of the heating and cooling coils 76 and 84 are not illustrated, a wide variety of commercial means including recorders may be employed with the gas treating device of the invention.

Referring to FIG. 4, another embodiment of the invention is illustrated and like numerals are utilized to designate parts similar to those that appear in the FIG. 3 embodiment. This embodiment is illustrated in a somewhat schematic manner since the only modification to the device is found in the construction of exhaust duct 17. Since the air curtains are moving at a rapid velocity, they have a tendency to scatter when they reach the fioor level thus the unit has been modified to provide structural means for aiding the flow of air to duct 17. Adjustable air direction bafiles 105 and 106 are secured to the lower portions of sides 45 and 46, respectively, and act to capture the curtain air and direct it into the perforated sides of the duct. As can be seen from the air flow as illustrated by the arrows, the air after reaching the zone of the exhaust duct is prevented from splashing over into the portion of the environment external of the patient zone.

The above description is primarily directed to the construction of the unique patient isolation unit and the manner in which this construction functions to maintain the patient zone at an extremely low contamination level and to avoid the invasion of the zone by airborne microorganisms.

This is obviously one of the important advantages of the unit, however, an equally important advantage is the ability of the unit to rapidly return the patient zone to the low operating level of contamination, i.e. the recovery rate, after bacteria have been introduced into the zone.

In order to optimize the recovery rate of the unit, the direction and velocity of air flow must be carefully selected. In other words, the air flow patterns must be designed to rapidly flush the patient zone free of bacteria and this must be accomplished with a minimum of air turbulence or roiling.

Referring to FIG. 3, it has been found that in order to maintain the integrity of air curtains 110 and 111, the initial velocity of the air flowing from air directing means 30 and 31 should fall within the range of 500 feet per minute to 3000 feet per minute with a preferred value of 1700 feet per minute. This insures that the major portion of the curtain air and essentially all of the internal air will be retained within the system and exhausted from the patient zone by exhaust duct 17. Tests have shown that for a normal volume of air supplied to the patient zone that the velocity of the air curtains with an initial velocity of 1700 feet per minute decreases to about 200 feet per minute at the floor level and again accelerates to about 500 feet per minute at the entrance to the exhaust duct 17.

The velocity of the air entering the patient zone through wall 25 is also significant since this has a marked effect on the flow conditions within the zone and the ultimate recovery rate of the unit. As shown by arrows 112 within the zone, the air is initially distributed vertically downwardly into the zone and then a definite division or splitting of the air occurs along the approximate longitudinal centerline of the patient zone. This division is created by the inductive effect of the higher velocity air curtains and it is this phenomenon that is thought to be responsible for the very high recovery rate of the unit. It has been found by experiment that the velocity of air 112 should fall within the range of feet per minute to 100 feet per minute and that the preferred velocity is 80 feet per minute. This velocity enables a portion of the air to descend to the bed level where it is induced to flow in a manner illustrated by arrows 113 in FIG. 3. Thus the entire body of air within the patient zone is continuously moving and sweeping the zone free of contamination without creating any stagnant or turbulant areas which would tend to impede the recovery of the system.

The results of a significant experiment are reproduced in FIG. 5 and these results dramatically illustrate the speed at which this unit can purge itself of bacteria. The experiment was performed in the following manner: with the unit running with the preferred air velocities indicated above, three Reynier slit samplers were placed on the bed with sampler No. l positioned approximately 22" from the head of the bed on the approximate ngitudinal centerline of the patient zone, sampler No. 2 was placed approximately 22" from sampler No. 1 toward the foot of the bed and sampler No. 3 was placed approximately 22" from sampler No. 2 toward the foot of the bed. A four milliliter aliquot of a suspension of Sarcina lutea containing approximately 10 million viable bacteria per milliliter was put into a Devilbiss No. 40 nebulizer and nebulized by a jet or air from a combination vacuum-pressure pump under a pressure of approximately pounds per square inch. The nebulizer was located within the patient zone approximately one foot from the head of the bed and one foot below the air supply plenum. The nebulizer was permitted to generate a bacteria laden mist for 2 minutes, which time is indicated on the graph of FIG. 5 as negative time. Zero time on the graph indicates the time at which the nebulizer was turned off and the bacteria count was begun. Since the number of bacteria colonies picked up by split sampler No. 1 during the first minute after nebulization was so extremely high and, in fact, too numerous to count, the curve representing this sampler is broken off at the top and continued at approximately the first second. The second curve represents the number of bacteria colonies appearing in slit sampler No. 2 and the lowest curve represents those picked up by slit sampler No. 3.

There are two very significant conclusions that can be drawn from the results of this experiment. First, the patient zone of the isolation unit, when the unit is operated in accordance with the preferred conditions, will be virtually completely cleared of bacteria within 2 minutes after bacteria have been either deliberately or accidentally introduced into the patient zone. Secondly, the patient zone will be cleared within 2 minutes regardless of the number of bacteria introduced into the patient zone and regardless of the location at which the bacteria are introduced.

What is claimed is:

1. An apparatus for isolating a patient zone from the external environment comprising in combination:

(1) a bed located adjacent the bottom of said zone;

(2) structural means for enclosing two opposed vertical sides of said zone;

(3) a plenum having at least one downwardly directed pervious wall positioned over said zone to enclose the upper portion thereof and to evenly distribute low velocity purified air vertically downwardly within said zone;

(4) an exhaust duct located under said bed, and

(5) means associated with the periphery of said plenum along the opposed structurally open sides of said zone for directing curtains of high velocity air between said periphery and said exhaust duct to completely enclose said zone.

2. The apparatus of claim 1 wherein said bed is positioned so that the longitudinal centerline thereof lies on the approximate longitudinal centerline of said zone and said structural means encloses the head and the foot portions of said bed.

3. The apparatus of claim 2 wherein said exhaust duct has a generally rectangular construction having a width not greater than the width of said bed and the vertical sides thereof are perforated to permit air to be drawn into said duct.

4. The apparatus of claim 3 further comprising bafile means associated with the lower portion of said exhaust duct for entrapping and directing air into said duct.

5. A method of isolating a patient zone from the external environment comprising the steps of:

(l) positioning a bed adjacent the bottom of said zone;

(2) structurally enclosing the top, bottom and two opposed sides of said zone;

(3) evenly distributing purified low velocity air vertically downwardly into said zone through said enclosed top;

(4) enclosing the remaining opposed two sides of said zone with high velocity air curtains; and

(5) exhausting said low and high velocity air through an exhaust duct located under said bed.

6. The method of claim 5 wherein said bed is positioned with the longitudinal centerline thereof approximately coinciding with the longitudinal centerline of said zone.

7. The method of claim 6 wherein said air curtains are symmetrically formed on opposite sides of said zone and said low velocity air is formed into two controlled air flow patterns which are produced by the inductive effect of said air curtains.

8. The method of claim 7 further comprising the steps of purifying the exhausted air and recirculating said purified air through said enclosed top and into said zone.

9. The method of claim 5 wherein said low velocity air is distributed at an initial velocity of from 5 to 100 feet per minute and said high velocity air has an initial velocity of from 500 to 3000 feet per minute and a terminal velocity of from 300 to 700 feet per minute.

10. The method of claim 9 wherein the initial velocity of said low velocity air is approximately 80 feet per minute and the initial and terminal velocities of said high velocity air are approximately 1700 feet per minute and 500 feet per minute, respectively.

References Cited UNITED STATES PATENTS 3,038,400 6/1962 Rufi 9836 3,380,369 4/1968 Allander 98-36 3,385,036 5/1968 Webb 9836 X FOREIGN PATENTS 481,991 3/1938 Great Britain.

10 WILLIAM E. WAYNER, Primary Examiner US. Cl. X.R.

S-362; 98-ll5; 128l45, 191

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U.S. Classification454/187, 454/189, 55/DIG.290, 55/DIG.180, 128/205.26, 96/223
International ClassificationA61G10/02, A61G11/00, F24F9/00, A61G13/00, F24F3/16, A61G7/00
Cooperative ClassificationA61G13/108, F24F3/1607, A61G11/00, A61G10/02, Y10S55/18, F24F9/00, Y10S55/29
European ClassificationF24F9/00, A61G11/00, A61G10/02, F24F3/16B3, A61G13/10V