Viral Transmission Barrier for Group Settings
20220378201 · 2022-12-01
Inventors
Cpc classification
International classification
Abstract
A viral transmission barrier for group settings such as school or workplace cafeterias.
Claims
1. A viral transmission barrier for tables with a height and a top surface with a length, a width, and a perimeter configured to accommodate a group of at least two people that may be strangers sitting in chairs at the perimeter and each having a section of table perimeter before them, the viral transmission barrier comprising, multiple vertical side panels each having a thickness sufficient to permit the vertical side panel to remain in a vertical position for a time exceeding 24 hours, a top edge, a height configured to extend at least the width of a hand of a sitting person above the head of any person sitting in a chair in front of the table perimeter, a length configured to have a first edge that extends outwardly beyond the perimeter of the table and a second edge, a separation between adjacent vertical side panels where they cross the table perimeter having a length of table perimeter of at least 18 inches (47 centimeters), and the multitude of vertical side panels is made of a material that sufficiently non-porous enough to prevents the transmission through the panel thickness of a virion of an airborne virus with a diameter of at least 50 nanometers and is resistant to degradation from exposure to disinfectant fluids, a neighboring vertical panel having a thickness sufficient to permit the vertical side panel to remain in a vertical position for a time exceeding 24 hours, a top edge, and a height configured to extend at least the width of a hand of a sitting person above the head of any person sitting in a chair in front of the perimeter of the table, and a length, and is made of a material that sufficiently non-porous enough to prevents the transmission through the panel thickness of a virion of an airborne virus with a diameter of at least 50 nanometers and is resistant to degradation from exposure to disinfectant fluids, a releasably attaching element attached to the second edge and a neighboring vertical panel with a seal that is sufficiently tight enough to prevent the passage through the seal of a viron of an airborne virus with a diameter of at least 50 nanometers and that is resistant to degradation from disinfectant fluids, and a horizontal ceiling panel releasably attached to the top edge of each perimeter panel.
2. The viral transmission barrier of claim 1 wherein the separation between adjacent vertical side panels where they cross the table perimeter has a length of table perimeter of at least 24 inches (61 centimeters).
3. The viral transmission barrier of claim 1 wherein the tabletop surface is circular, and the neighboring vertical panel is a vertical side panel.
4. The viral transmission barrier of claim 1 wherein the top surface of the table is circular, and the neighboring vertical panel is a cylinder with an outer surface configured with multiple releasably attaching elements configured to releasably attach to the second edge of a multitude of vertical side panels.
5. The viral transmission barrier of claim 1 wherein the top surface of the table is square with a length and a width that are equal, and the neighboring vertical panel is a vertical side panel.
6. The viral transmission barrier of claim 1 wherein the top surface of the table is rectangular with a length and a width that is shorter than the length, and the neighboring vertical panel is a vertical back panel configured to pass down the center of the length of the table and having outer surfaces and multiple releasably attaching elements configured to releasably attach to the second edge of a multitude of vertical side panels.
7. The viral transmission barrier of claim 1 wherein the vertical side panels have lengths configured so that at least some first edges on the lengths extend outwardly at least 5 inches beyond the perimeter of the table.
8. The viral transmission barrier of claim 1 wherein the distance of perimeter between where first ends of adjacent vertical side panels cross the perimeter of the table is at least 30 inches.
9. The viral transmission barrier of claim 1 wherein at least some of the multitude of the vertical side panels are configured to transparent to permit the viewing of a person through the panels.
10. The viral transmission barrier of claim 1 wherein at least some of the neighboring vertical panel are configured to transparent to permit the viewing of a person through the panels transparent.
11. The method of using a viral transmission barrier to prevent the transmission of airborne viral particles from an infected person to others of a group of at least two people that may include strangers and are siting in chairs at a table with a perimeter and each having a section of table perimeter before them at a function where masks are not worn, the method comprising the steps of, providing a table and chairs for seating a group of at least two people; providing a virial barrier for tables with a height and a top surface with a length, a width, and a perimeter configured to accommodate a group of at least two people that may be strangers sitting in chairs at the perimeter and each having at least 24 inches of perimeter before them, the viral transmission barrier comprising, multiple vertical side panels having a thickness sufficient to permit the vertical side panel to remain in a vertical position for a time exceeding 24 hours, a top edge, a height configured to extend at least the width of a hand of a sitting person above the head of any person sitting in a chair in front of the table perimeter, a length configured to have a first edge that extends outwardly beyond the perimeter of the table and a second edge, a separation between adjacent vertical side panels where they cross the table perimeter having a length of table perimeter of at least 18 inches (47 centimeters), and the multitude of vertical side panels is made of a material that sufficiently non-porous enough to prevents the transmission through the panel thickness of a virion of an airborne virus with a diameter of at least 50 nanometers and is resistant to degradation from exposure to disinfectant fluids, a neighboring vertical panel having a thickness sufficient to permit the vertical side panel to remain in a vertical position for a time exceeding 24 hours, a top edge, and a height configured to extend at least the width of a hand of a sitting person above the head of any person sitting in a chair in front of the perimeter of the table, and a length, and is made of a material that is sufficiently non-porous enough to prevents the transmission through the panel thickness of a virion of an airborne virus with a diameter of at least 50 nanometers and is resistant to degradation from exposure to disinfectant fluids, a releasably attaching element attached to the second edge and a neighboring vertical panel with a seal that is sufficiently tight enough to prevent the passage through the seal of a viron of an airborne virus with a diameter of at least 50 nanometers and that is resistant to degradation from disinfectant fluids, and a horizontal ceiling panel releasably attached to the top edge of each perimeter panel; releasably affixing the viral transmission barrier on top of the table; seating people at the table to perform activities that require removal of masks; replacing people with other people as tasks are finished.
12. The method of claim 11, wherein the tabletop surface is circular, and the neighboring vertical panel is a vertical side panel.
13. The method of claim 11, wherein the top surface of the table is circular, and the neighboring vertical panel is a cylinder with an outer surface configured with multiple releasably attaching elements configured to releasably attach to the second edge of a multitude of vertical side panels.
14. The method of claim 11, wherein the top surface of the table is square with a length and a width that are equal, and the neighboring vertical panel is a vertical side panel.
15. The method of claim 11, wherein the top surface of the table is rectangular with a length and a width that is shorter than the length, and the neighboring vertical panel is a vertical back panel configured to pass down the center of the length of the table and having outer surfaces and multiple releasably attaching elements configured to releasably attach to the second edge of a multitude of vertical side panels.
16. The method of claim 11, wherein the vertical side panels have lengths configured so that at least some first edges on the lengths that extend outwardly at least 6 inches beyond the perimeter of the table.
17. The method of claim 11, wherein the vertical side panels have a length that extends the first edge at least 5 inches beyond the perimeter of the table.
18. The method of claim 11, wherein the distance of perimeter between where first ends of adjacent vertical side panels cross the perimeter of the table is at least 30 inches.
19. The method of claim 11, wherein at least some of the multitude of vertical side panels are configured to transparent to permit the viewing of a person through the panels.
20. The method of claim 11, wherein at least some of the neighboring vertical panels are configured to transparent to permit the viewing of a person through the panels transparent.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The invention will become more fully understood by the accompanying drawings, wherein like elements are represented by like reference characters, that are given by way of illustration only and thus are not limitative of the example embodiments herein.
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[0036] While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail below. It is to be understood, however, that the intention is not to limit the invention to the embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION
[0037] The invention of a viral transmission barrier in group settings was developed as a way bot prevent viral spread where the wearing of masks ids not practical, such as, for example, in assisted living facility, workplace and school cafeterias while eating. A series of experiments were conducted to evaluate the distance of simulated respiratory droplet spread and the effectiveness of applying masks and barriers as a mitigation strategy to improve safety.
[0038] Activities such as speaking, coughing, sneezing and even breathing produce oral and nasal droplets containing viral particles. Mitigation efforts aimed at tackling COVID-19 spread include covering a person's face with a mask, social distancing, and regular hand washing, appear to be somewhat effective if correctly done. This study was conducted to evaluate the distance of simulated respiratory droplet spread and the effectiveness of applying masks to particles, and barriers as a mitigation strategy to improve safety. Activities such as speaking, coughing, sneezing and even breathing produce oral and nasal droplets containing viral particles.
[0039] There appear to be two components of a sneeze or cough, a ballistic droplet component and a turbulent gas or puff component which have been visualized using high speed videography, distortion of projected schlieren light beams and shadowgraph imaging. The velocity of the cough airflows has been measured as high as 46 feet per second (ft/s) (14 meters/second (m/s)). The horizontal distance of a gas cloud after a cough or sneeze may travel more than 26.2 feet (ft) (8.0 meters (m)) and aerosol transport has been documented at a distance of 13.1 ft (4.0 m). The size of particles ejected during a cough or sneeze ranges from 0.1 to 1000 μm with large droplets called macroscopic droplets having diameters of 1 to 1000 μm or larger and aerosols, called microscopic droplets having diameters of from 1 to 0.1 μm. 90% of viral transmission is now believed to be from aerosol particle under 1 μm. Mathematical models have been used to calculate the effect of drag, diffusion, gravity, humidity, temperature and wind flow on the velocity and distances traveled by respiratory droplets.
[0040] While it was previously thought that larger droplets fall to the ground after a short distance, smaller yet still macroscopic droplets may travel farther and be predominantly responsible for transmitting disease. One model of respiratory droplet spread has involved the use of fluorescent dye in a small latex balloon which is inflated until it bursts. The droplets produced have been visualized with an ultraviolet light. This model has been used in multiple experiments to examine the spread of droplets in clinical and surgical settings, with and without masks and various barriers. Surgical masks have been shown to alter and reduce the respiratory jets and droplet spread from coughs and sneezes.
[0041] One of the main challenges during the COVID-19 pandemic is the lack of safety measures and guidelines to reduce the risk of viral spread among people during gatherings. A study was conducted to evaluate the distance of oral and nasal droplet spread in a model that simulates coughing and sneezing in a public setting, specifically a school setting, to guide faculty and staff members with safety measures and guidelines to reduce droplet spread. Results could be extended to other public settings such as, for example, workplace and assisted living facility cafeterias. Several models were prepared to observe and visualize the spread of fluid simulating respiratory droplets in places such as the classroom and the cafeteria, in which a student would be more susceptible to contract a virus since individuals cannot wear masks while eating. For all trials, a 1.0 in. (2.5 cm) balloon with 0.3 milliliter (ml) of diluted fluorescent paint was placed inside a mannequin head and was exploded outwards from the mannequin's mouth at 5 pounds per square inch (psi) to generate droplets with an average diameter 100 to 300 μm. Using a black light, the expelled fluorescent macroscopic droplets were visualized. When applying safety precautions and guidelines such as mandating face masks, the results of the experiments conducted in this study with a surgical mask, were extremely positive for the size droplets studied. However, without other safety precautions such as face masks and barriers, social distancing proved to be ineffective. In conclusion the most effective way to prevent droplet spread during activities where masks simply cannot be worn, such as eating, is to apply a viral transmission barrier of the invention between the individuals. Applying viral transmission barriers and properly wearing masks successfully prevented macroscopic droplet spread. For microscopic-sized droplets, only viral transmission barriers still would be effective. Masks would need to be used that could screen smaller particles than surgical masks that were used in this study.
[0042] Understanding the maximum spread of oral droplets may assist in producing more effective measures to combat COVID-19 and protect students and faculty when returning to school. The Centers for Disease Control and Prevention (CDC) until recently has recommended that people should practice social distancing at least 6 feet apart in combination with other preventative measures such as wearing face masks. However, many people believe that only social distancing is effective in preventing the spread of COVID-19, leading them to believe that they are safe, when in fact they may not.
[0043] As a result of the study that is discussed later, a viral transmission barrier in group settings has been invented that is effective in preventing the spread of COVID-19 and other airborne virus particles where wearing masks is not practical. There are two aspects to the invention, an article aspect and a method of using aspect.
[0044] The article aspect is a viral transmission barrier for tables with a height and a top surface with a length, a width, and a perimeter configured to accommodate a group of at least two people that may be strangers sitting in chairs at the perimeter and each having a section of table perimeter before them. The viral transmission barrier comprises an article aspect and a method aspect. Specifically, the article aspect comprises four elements, a multitude of vertical side panels, at least one neighboring vertical panel, a releasably attaching element, and a horizontal ceiling panel.
[0045] The first element is the multiple vertical side panels where each has a thickness sufficient to permit the vertical side panel to remain in a vertical position for a time exceeding 24 hours, a top edge, and a height configured to extend at least the width of a hand of a sitting person above the head of any person sitting in a chair in front of the table perimeter. Each also has a length configured to have a first edge that extends outwardly beyond the perimeter of the table and a second edge. There is a separation between adjacent vertical side panels where they cross the table perimeter having a length of table perimeter of at least 18 inches (47 centimeters). Each is made of a material that is sufficiently non-porous enough to prevents the transmission through the panel thickness of a virion of an airborne virus with a diameter of at least 50 nanometers and is resistant to degradation from exposure to disinfectant fluids.
[0046] The dimensions are configured to provide a comfortable eating space in a cafeteria setting that also bars forward and lateral transmission of viral particles. The thickness should be sufficient for the vertical side panels to remain in a vertical position for a time exceeding 24 hours. Lengths of adjacent side panels provide a space in the table perimeter where adjacent vertical side panels cross over the table perimeter that is at least 18 in (47 cm) to comfortably accommodate people at the table that may be children. Some embodiments have a table perimeter space of at least 24 in. (61 cm), some at least 26 kn. (66 cm), some at least 28 in. (71 cm), and some at least 30 in. (76 cm) where larger people are to be accommodated such as office cafeterias. The height is sufficient to achieve comfort for the people sitting at the table and may depend upon the age of the people. Elementary school students may have a maximum height less than high school students where the height extend at least the width of a hand of a sitting person above the head of any person sitting at the table. In some embodiments, the height may extend at least 4 in. (10 cm), in some at least 5 in. (13 cm), in some at least 6 in. (15 cm), and in some at least 7 in. (18 cm) above the head of the tallest person that the viral transmission barrier is configured to accommodate. The first edge of the table extends outward beyond the perimeter of the table to block lateral viral transmission. In some embodiments the extension is at least 5 in. (13 cm), in some 6 in. (15 cm), in some at least 7 in (18 cm), and in some at least 8 in. (20 cm).
[0047] The material has several properties. It must be rigid to allow it to remain vertically positioned for at least 24 hours. It must be sufficiently non-porous enough to prevents the transmission through the panel thickness of a virion of an airborne virus with a diameter of at least 50 nanometers and is resistant to degradation from exposure to disinfectant fluids. In addition, some embodiments are transparent, i.e., enabling people sitting before the viral transmission barrier while performing a task such as eating to see others sitting at the table and possibly communicating with them without having the urge to look around the viral transmission barrier to see others. Transparency fosters a sense of community and not one of isolation. Suitable materials include plastics such as Plexiglass and glass.
[0048] The second element is the at least one neighboring vertical panel that has a thickness sufficient to permit the vertical side panel to remain in a vertical position for a time exceeding 24 hours, a top edge, a height configured to extend at least the width of a hand of a sitting person above the head of any person sitting in a chair in front of the perimeter of the table, and a length. It also is made of a material that sufficiently non-porous enough to prevents the transmission through the panel thickness of a virion of an airborne virus with a diameter of at least 50 nanometers and is resistant to degradation from exposure to disinfectant fluids. The height and materials are similar to that of the vertical side panels. In some embodiments the neighboring vertical panel is the same as a vertical side panel, in some it is a cylinder configured to be attached to multiple vertical side panels at a distance away from the center of the table, and in some it is a panel extending down the middle of the length of a table.
[0049] The third element is the releasably attaching element that is attached to the second edge and a neighboring vertical panel with a seal that is sufficiently tight enough to prevent the passage through the seal of a viron of an airborne virus with a diameter of at least 50 nanometers and that is resistant to degradation from disinfectant fluids. Such a seal is known to the industry and include, for example, (1) round cylindrical base rods affixed to multiple outward extensions with U-shaped cross-sections configured to friction-fit to the second edges of the vertical side panels; (2) flat bases with one side configured to attach to a neighboring vertical panel and the other side having an outward protrusion with a U-shaped cross-sections configured to friction-fit to the second edge of a vertical side panel; and two-part adhesive-backed mechanical fastening tapes configures to adhere to both the sides of vertical side panel at its second end and the length of a neighboring vertical panel to form a seal between two panels. One example of material that may be used for the releasably attaching elements is rubber or another thermoset elastomer.
[0050] The fourth element is the horizontal ceiling panel is releasably attached to the top edge of each perimeter panel. This may be made of similar materials as used for the vertical side panels or other materials the are as rigid but less transparent, such as plastics or wood. Generally, materials like those used for the vertical panels are more desirable to encourage a greater sense of community.
[0051] The table on which the invention is releasably attached may be round, square, or rectangular. They generally provide a section of perimeter for each person seated before the table of at least 18 in. (47 cm) to 30 in. (76 cm) or larger. Dimensions are provided for common tables but are not meant to limit the scope of the invention. Round tables commonly have a dimeter of 42 in. (107 cm) and seat 3 people comfortably. Larger tables may be used with larger diameters and seat 8 people comfortably. Square tables have various side dimensions of at least 30 in. (76) or larger and generally seat 4 people comfortably. Rectangular tables, commonly used in school cafeterias, generally have a width of at least 60 in. (152 cm) and a length of at least 120 in. (305 cm), and generally seat 8 people comfortably with a perimeter of at least 30 in. (76 cm).
[0052] In some embodiments, the tabletop surface on which the viral transmission barrier is releasably attached is circular and the neighboring vertical panel is a vertical side panel. It may cover part of the table or predominately most of the table as desired. Some embodiments are used for large gatherings while other are used to isolate some from large groups.
[0053] Because the use of viral transmission barriers for group settings may change with the presence of the infection in the community or the use of the room, some embodiments of the viral transmission barriers may be configured to be disassembled and stored for later use as the tables often are so configured. Viral transmission barriers may contact the top of tables differently. In some embodiments, the viral transmission barrier rests upon the top of a table. In some embodiments, the viral transmission barrier is releasably attached to the top of a table.
[0054] The viral transmission barrier of the invention is suitable for tables of different shapes. Depending on the shape of the table, the nature of the neighboring vertical panel may be different. In some embodiments, wherein the top surface of the table is circular with a diameter of around 42 in. (107 cm), the neighboring vertical panel is the same as a vertical side panel and the second ends of each are releasably connected to each other with a releasably attaching element.
[0055] In some embodiments, wherein the top surface of the table is circular with a diameter of more than 50 in (127 cm), the neighboring vertical panel of the viral transmission barrier is a cylinder with an outer surface configured with multiple releasably attaching elements configured to releasably attach to the second edge of a multitude of vertical side panels.
[0056] In some embodiments, wherein the top surface of the table is circular, the neighboring vertical panel of the viral transmission barrier is a cylinder with an outer surface configured with multiple releasably attaching elements configured to releasably attach to the second edge of a multitude of vertical side panels. This occurs when the circular table has a diameter large enough to seat up to 6 to 10 people comfortably.
[0057] In some embodiments, where the top surface of the table is square with a length and a width that are equal, the neighboring vertical panel of the viral transmission barrier is a vertical side panel, and the second ends of each are releasably connected to each other with a releasably attaching element, like with the viral transmission barrier on the small circular table discussed above.
[0058] In some embodiments, where the top surface of the table is rectangular with a length and a width that is shorter than the length, the neighboring vertical panel of the viral transmission barrier is a vertical back panel configured to pass down the center of the length of the table and having outer surfaces and multiple releasably attaching elements configured to releasably attach to the second edge of a multitude of vertical side panels. In some embodiments, the releasable attaching element are on both sides of the vertical back panel, and multiple vertical side panels are releasably attached and extend outward to the nearest long length of the table. In some embodiments, the neighboring vertical panel of the viral transmission barrier is a vertical back panel configured to pass down one edge of the length of the table and having outer surfaces and multiple releasably attaching elements on one side configured to releasably attach to the second edge of a multitude of vertical side panels. In some embodiments, the vertical back panel has a length that runs short of the ends of the table. In some embodiments the vertical back panel has a length that runs to the end of the table. In some embodiments, the vertical back panel extends beyond the ends of the table.
[0059] The method aspect is aa method of using a viral transmission barrier to prevent the transmission of airborne viral particles from an infected person to others of a group of at least two people that may include strangers and are sitting in chairs at a table with a section of table perimeter before each of them at a function where masks are not worn. Specifically, the method comprises five steps.
[0060] The first step is providing a table and chairs for seating a group of at least two people.
[0061] The second step is providing a virial barrier as discussed above.
[0062] The third step is releasably affixing the viral transmission barrier on top of the table.
[0063] The fourth step is seating people at the table to perform activities that require removal of masks.
[0064] The fifth step is replacing people with other people as tasks are finished.
[0065] Figures of various embodiments of the viral transmission barrier invention may further increase understanding of the invention.
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[0074] The study that led to discovery of the above invention consisted of eight experiments, each done with three trials. The following are descriptions of the materials and methods used, the nine experiments conducted, and results gained.
Materials and Methods
[0075] For each experiment three trials were conducted in a ventilated room simulating a classroom or cafeteria. The tables used in experiments 3 through 6 were adjusted to mimic the exact table dimensions in a local high school cafeteria. The school table dimensions were 10.0 ft or 120.0 in. (306.1 cm) in length, 37.0 in. (94.0 cm) in width, and 30 in. (76.2 cm) in height. In addition, the chairs in the high school cafeteria were 19.0 in (48.3 cm) in height, and the chairs used in this experiment were the same height. For each trial only one mannequin head (M1) simulated a student coughing. To ensure non-contamination and efficiency between each experiment, tablecloths, (from Paper Art Co., Inc., Indianapolis, Ind., U.S.A.), clear plastic wraps (from Polyvinyl Films, Inc., Sutton, Mass., U.S.A,) and plastic bags (from Fleet Farm, Brooklyn Park, Minn., U.S.) were placed on the tables, mannequin heads (from FloraCraft Corporation, China,) and body and replaced after each experiment. In addition, three different colors of fluorescent paint (from Testors Craft, Hawthorn Pkwy, Vernon Hills, Ill., U.S.)—orange, green, and pink—were used for each trial with one color being used per trial. This would allow clear distinction between each trial run. To mimic the viscosity of saliva, 1 mL of fluorescent paint was diluted with the same volume of water. A wooden frame was built around a mannequin mask (from Creatology, China) to simulate a laryngeal cough from the interior, while also resembling a person's head. Plastic was attached between the wooden frame and the mask, and on the eyes, to ensure droplets were only exiting from the mouth and nasal cavity. The mannequin's mouth was cut in a circular shape and had a diameter of 2.0 in. (5.1 cm), and the nostrils were cut the same way and had a diameter of 0.50 in. (1.27 cm to simulate the measurements of a student's mouth and nostrils when coughing. These measurements were obtained from the author's mouth and nostrils as shown in
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[0078] The purpose of the first five experiments was to simulate the spread of droplets from a student's unprotected cough while seated in a cafeteria setting. The last three experiments were designed to study the spread of droplets and the effectiveness of a mask when standing in an open space such as a hallway.
[0079] The first experiment was designed to determine the maximum spread of droplets traveling straight outward from M1. In
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[0081] Similarly, the second experiment was designed to measure the lateral distance of droplet spread. As shown in
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[0083] For the third experiment, 10 mannequins were oriented in normal eating positions without social distancing measures to examine the spread of droplets. A reasonable distance was used to simulate normal seating positions of students in a cafeteria by orienting them 10.0 in. (25.4 cm) shoulder width apart. All mannequins were aligned symmetrically. Going clockwise from M1, the mannequins were named in consecutive numbers, as shown in
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[0085] The purpose of the fourth experiment was to identify the maximum height of droplet spread on the barrier as well as on the top cover of the barrier to determine a sufficient barrier height and whether a top cover was necessary in order to prevent droplets from spreading to the surrounding mannequins and table. To determine if droplets could travel over the barrier, Plexiglass was placed over the top of the barrier. Like the third experiment, the nine other surrounding mannequins were seated in normal eating positions with a barrier around M1, as shown in
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[0087] In the fifth experiment, the positions of each mannequin remained constant as in the previous experiment. The two side walls of the barrier were extended off the edge of the table by 7.0 in. (17.8 cm) while the eating space remained the same as shown in
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[0089] The purpose of the sixth, seventh, and eighth experiments was to simulate the spread of droplets from a person coughing without a mask, with a mask worn improperly, as shown in
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[0091] Droplet sizes were measured in experiments three, four, and five with a digital fractional caliper (Ironton, China) with an accuracy of 0.51 mils or 0.013 millimeters (mm) (13 μm)). A total of 67 droplets were measured. The diameter of the largest droplets ranged from 37.4 mils (0.95 mm or 950 μm) to 0.14 in. (3.57 mm or 3457 microns), while the diameter of the smallest droplets ranged from 8.7 mils (0.22 mm or 2220 μm) to 35.8 mils (0.91 mm or 910 μm). Most of the droplets were less than 39.4 mils (1 mm or 1000 μm) in diameter. While these were considerably larger than the diameter of droplets believed to be carrying virus infections as discussed earlier, it is believed that the conclusions of these experiments are still valid. Smaller droplet size wound be expected to travel farther but evaporate more quickly resulting in an unknown resulting distance from coughs.
Results
[0092] The results are separated by experiment type, and the distances of droplet spread are listed in ft or in. and cm. The purpose of the first experiment was to examine the maximum distance of frontal droplets spread. The maximum distance of droplets traveling straightforward from M1 was 8.9 ft or 107.2 in. (272.4 cm) with a range of 6.0 ft or 71.5 in. (181.6 cm) to 8.9 ft or 107.2 (272.4 cm) as shown in
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[0094] In the second experiment, which was designed to determine the maximum lateral dispersion of droplets, the maximum distance of droplets traveling to the left of M1 was 6.6 ft or 79.0 in. (200.7 cm) with a range of 5.6 ft or 67.0 in. (170.2 cm) to 6.6 ft or 79.0 in. (200.7 cm). Similarly, the maximum distance of droplets traveling to the right of M1 was 6.1 ft or 72.8 in. (184.8 cm) with a range of 4.4 ft or 52.2 in. (132.7 cm) to 6.1 ft or 72.7 in. (184.8 cm) as shown in
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[0096] In experiment three, which was designed to examine the spread of droplets in a cafeteria or classroom setting at a table, macroscopic droplets were found on every mannequin as well as in all their eating spaces, which was within at least 15.0 in. (38.1 cm) from the mannequin. Droplets were found on the bodies and heads of the surrounding mannequins as shown in
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[0098] The fourth experiment was designed to determine the height of droplet spread on the barrier, as well as whether droplets spread on the inside of the top cover and anywhere outside the barrier. As shown in
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[0100] The fifth experiment was designed to test whether droplets were found on surfaces other than the extended barrier. As shown in
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[0102] The sixth, seventh, and eighth experiments were designed to observe the effectiveness of a surgical mask in preventing droplet spread. As shown in
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[0104] The finding that there were droplets found on the inner surface of the surgical mask (the inside surface of the mask facing the nose and mouth) during each separate trial in Experiment Seven where masks were worn improperly and Experiment Eight where masks were worn properly but not in the space or surfaces around M1 with the mask worn properly, led to the deduction that the mask was preventing droplet spread. Although the assessment of droplet spread on the surrounding surfaces around M1 was performed immediately after the simulated cough, it is possible that rapid evaporation could have led to an underestimate of any droplets that might have penetrated the mask and evaporated prior to observation of the droplets remaining on the surfaces around M1. However, that would presume that there would be no residual fluorescent residue remaining on the surrounding surfaces after potential evaporation and although that is possible, it seems less likely. It is also possible that the large size of the droplets, averaging 100 microns in diameter, may have resulted in a false conclusion that masks worn properly would prevent transmission of droplets. In 2009, four researchers examined how well surgical masks worked to filter small particles, those of 1 micron (1000 nanometers) or less. In a paper called “Filtration performance of FDA-cleared Surgical Masks”, the scientists tested five surgical mask brands. Most mask brands allowed 15 percent or more of 100-nanometer (viron-size) to 1-micron diameter particles through. At least one allowed more than half of those particles through.
Discussion
[0105] As schools begin plans to reopen, safety precautions and guidelines need to be established to protect students and teachers from respiratory droplet spread in order to mitigate transmission and infection from COVID-19. The experiments conducted in this study help clarify some characteristics of macroscopic droplet spread which can aid in the implementation of safety measures.
[0106] It is not completely known whether respiratory macroscopic droplets can spread beyond 6 ft (1.8 meters (m)). Although, a recently published study showed a simulated jet containing microscopic droplets traveling up to 12 ft (3.6 m), and another recent study show that turbulent gas clouds can travel 23-27 ft (7.0-8.2 m). However, while suspected by some, it is not proven at this time that microscopic respiratory jets are the predominant mechanism of disease transmission from COVID-19. In fact, macroscopic droplets may be more likely the predominant mechanism involved in disease transmission since many outbreaks such the 1981 outbreak of infectious meningitis in a Texas elementary school involving students who became infected while seated within less than 3 ft (0.9 m) of the first person infected. In this case one could hypothesize that it was the shorter traveling larger droplets that landed on the children which caused the infection, rather than microscopic droplets which are known to travel over 12 ft (3.6 m) away or gas clouds travelling up to 23-27 ft (7.0-8.2 m) away, where none of the other students were infected. In the study described above, it became clear that social distancing at 6 ft (1.8 m) alone was not effective at preventing macroscopic droplet spread. In multiple trials, sitting or standing without a mask or barrier, the maximum distance of macroscopic droplets was found farther than 6 ft (1.8 m) from the mannequin simulating the cough. In the experiments simulating a cafeteria setting, droplets were found in the majority of the other mannequins' eating space. Although it may not seem harmful, if infectious droplets land in one's food, one could be infected. However, when applying a barrier, droplet spread was less. Furthermore, when extending the sides of the barrier 7 in. (17.8 cm) beyond the table perimeter on both sides of M1, the results showed a more protective effect. There was no droplet spread to any of the surrounding mannequins as well as anywhere outside the barrier when a top was included. This would seem to provide protection from sideways spread of droplets that could travel to and infect a person sitting next to the person coughing.
[0107] One of the weaknesses of the experiments that were conducted was that only three trials were conducted for each experiment, whereas a larger number of trials would have enabled a more sophisticated statistical analysis. In addition, the mannequins in each experiment were only facing straight, whereas human beings are constantly moving. Moreover, because all experiments were conducted in a ventilated room, droplet spread could have been influenced. Furthermore, an air compressor was used to inflate a balloon filled with fluorescent paint to simulate the cough. If a real human being was used during these experiments, the results may have been different. The viscosity of the fluorescent paint was diluted to mimic the viscosity of saliva. However, the viscosity of the solution or of saliva was not measured. In addition, it was not known whether a cloth mask or an N95 mask would perform differently in these experiments. However, despite these challenges, the strengths of these experiments include the generation of valuable information on droplet spread from a simulated cough. These experiments have consistently shown that macroscopic droplets travel farther than was previously thought. This appears to be the first study to report data on droplet spread using barriers in a cafeteria type setting. In addition, the information provided in this study can help guide mitigation efforts in preventing droplet spread. The prevention of droplet spread can help reduce transmission of the COVID-19 virus during this global pandemic and other airborne invention s in the future.
CONCLUSIONS
[0108] Based on the results of these experiments, social distancing at a distance of 6 ft (1.8 m) without a mask or barrier was ineffective at preventing droplet spread. However, a surgical mask was effective at preventing droplet spread anywhere beyond the mask of the coughing mannequin for the size droplets studied. But this would not apply to situations where mask wearing is impractical such as while eating in a cafeteria.
[0109] Physical barriers should be established in places where masks are not worn, such as cafeterias in schools, workplaces, or assisted living facilities to limit droplet spread. Clear barriers would seem prudent so that students, workers, or residents would be less likely to lean back to see or to talk to other students, workers, or residents. A barrier that was aligned with the edge of the table was not sufficient to prevent lateral droplet spread. However, lateral droplet spread was eliminated when the barrier was extended to 7 in. (17.8 cm) outwardly beyond the edge of the table on both sides of M1. In addition, droplets were consistently found on the top cover of the barrier, meaning that droplets could travel over the barrier unless a top was included with the barrier. When the barrier extended past the edge of the table with a top, it effectively prevented droplets from spreading anywhere outside the barrier. Based on these findings, it would be prudent for barriers to be constructed following the structure of the viral transmission barriers disclosed above and claimed.
[0110] Wearing a mask properly over the mouth and nose or utilizing barriers where masks cannot be worn, such as cafeterias, were effective in preventing macroscopic droplet spread of the droplet size studied. While the effect of masks may change when considering particles from a turbulent cloud, it is not expected to affect the viral transmission blocking benefits of a viral transmission barrier as described above and claimed.
[0111] Most importantly, this series of experiments can help guide schools, workplaces, and nursing homes to establish safety guidelines and precautions as they re-open to prevent droplet spread both in the classroom and in the cafeteria setting.