The spread of macroscopic droplets from a simulated cough with and without the use of masks or barriers.

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. This 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. 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 2.54 centimeter balloon with 0.3 milliliters 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). 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. 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 barriers between the individuals. Applying barriers and wearing masks successfully prevented macroscopic droplet spread.

Introduction

Mitigation efforts aimed at tackling COVID-19 spread, with recommendations including covering a person’s face with a mask, social distancing, and regular hand washing, appear to be effective [1]. This study was 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. Activities such as speaking, coughing, sneezing and even breathing produce oral and nasal droplets containing viral particles [2-5].

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 [6-11]. The velocity of the cough airflows has been measured as high as 14 m/s [10, 12]. The horizontal distance of a gas cloud after a cough or sneeze may travel more than 8 meters and aerosol transport has been documented at a distance of 4 meters [13]. The size of particles ejected during a cough or sneeze ranges from 0.1 to 1000 microns [14]. 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 [15].

While it was previously thought that larger droplets fall to the ground after a short distance, smaller yet macroscopic droplets may travel farther and be predominantly responsible for transmitting disease [16].

One model of respiratory droplet spread has involved the use of fluorescent dye in a small latex balloon which is inflated until it bursts [17-19]. The droplets produced have been visualized with an ultraviolet light [17-20]. 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 [17-21]. Surgical masks have been shown to alter and reduce the respiratory jets and droplet spread from coughs and sneezes [9, 19–23]. The experiments in this manuscript utilized the model of respiratory droplet spread described above.

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 CDC recommends that people should practice social distancing at least 6 feet apart in combination with other preventative measures such as wearing face masks [24]. However, the majority of 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 are not.

Materials and methods

For each experiment three trials were conducted in a ventilated room simulating a classroom or cafeteria. The tables in experiments 3 through 6 were adjusted to mimic the exact table dimensions in the Blake High School cafeteria. The school table dimensions were 306.07 centimeters in length, 93.98 centimeters in width, and 76.2 centimeters in height. In addition, the chairs in the Blake High School cafeteria were 48.26 centimeters 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 (Paper Art Co., Inc., Indianapolis, Indiana, U.S.A.,) clear plastic wraps (Polyvinyl Films, Inc., Sutton, MA, U.S.A,) and plastic bags (Fleet Farm, Brooklyn Park, MN, U.S.A.) were placed on the tables, mannequin heads (Florocraft, China,) and body and replaced after each experiment. In addition, three different colors of fluorescent paint (Testors Craft, Hawthorn Pkwy, Vernon Hills, IL, U.S.A.,) 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, 1mL of fluorescent paint was diluted with the same volume of water. A wooden frame was built around a mannequin mask (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, as well as on the eyes, in order 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 5.08 centimeters, and the nostrils were cut the same way and had a diameter of 1.27 centimeters in order 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 Fig 1B, and the author has the body habitus of a typical high school student. Two screws were placed on the sides of the wooden frame in order to attach the ear loops of a mask to mimic the top and bottom points of an ear as shown in Fig 1C. Depending on the simulation, whether the mannequin was sitting down or standing up, respectively, two or three identical boxes (Fellowes, U.S.A) covered with plastic bags which were replaced between each experiment, were placed underneath the wooden frame of the mannequin mask as well as other mannequin heads. These boxes were not only used to support the head of the mannequins but also to simulate the body of a student. All the heights of the mannequins were based off of the measurements of the author when sitting at a height of 134.62 centimeters and standing at a height of 177.8 centimeters. To simulate the cough, an air compressor (Bostitch, U.S.A.) was used to fill a 2.54 centimeter long latex balloon (Toysmith, Taichung, Taiwan) filled with 0.3mL of the diluted fluorescent paint, a reasonable volume of fluid that one might expel when coughing, at the mouth of the mannequin mask and inflated at 5 psi until it burst [17]. Five psi has been previously reported as the pressure of a laryngeal cough [18, 25]. After each trial, a black light (Vansky, China) was used in order to observe and record the spread of droplets as shown in Fig 2A–2C. A white metric measuring tape with centimeter and millimeter markings (Lufkin, U.S.A.) was used to measure the distance of droplet spread.

Fig 1

Dimensions and different views of M1.

A white metric measuring tape with centimeter and millimeter markings is shown in each figure. (A) The front of the mannequin head is displayed. The head consists of a wooden base and frame as well as plastic connected to the mask and frame. (B) The measurements of the nostrils and mouth are shown. (C) The side view of M1 is displayed as well as two screws which were used to simulate the human ear to anchor the mask.

Fig 2

Droplets on surrounding surfaces.

A white metric measuring tape with centimeter and millimeter markings is present in each figure. (A) Fluorescent paint droplets can be visualized on the table by illumination with a black light. (B) Five fluorescent paint droplets were found on the forehead of one of the mannequins surrounding M1. (C) Arrows point to five fluorescent paint droplets on the head of the mannequin.

The purpose of the first six 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.

The first experiment was designed to determine the maximum spread of droplets traveling straight outward from M1. As shown in Fig 3B, M1 was seated, measuring 134.62 centimeters tall, at one far end of the table. The length of the table was 306.07 centimeters.

Fig 3

Frontal droplet spread when sitting simulation.

A white metric measuring tape with centimeter and millimeter markings is displayed in each figure. (A) A bird’s eye view photo of the full table in front of the mannequin simulating the cough is shown. (B) The exact measurement of the table is labeled, and the mannequin is labeled as M1.

Similarly, the second experiment was designed to measure the lateral distance of droplet spread. As shown in Fig 4B, M1 was placed in the middle of the long side of the table which was 459.70 cm in length. M1 was placed at the middle of the table to measure the maximum spread of droplets traveling to both sides. The maximum distance of droplet spread on both sides of M1 were recorded.

Fig 4

Lateral droplet spread when sitting.

A white metric measuring tape with centimeter and millimeter markings is shown in each figure. (A) A bird’s eye view photo of the mannequin simulating the cough, placed in the middle of a long table, is displayed. (B) The measurement of the length of the table is shown and the mannequin at the center is labeled M1.

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 to simulate normal seating positions of students in a cafeteria was by orienting them 25.40 centimeters shoulder width apart. All mannequins were aligned symmetrically. Going clockwise from M1, the mannequins were named in consecutive numbers, as shown in Fig 5B. The distance from M1’s mouth to the other mannequins’ bodies was 53.34 centimeters to M2 as well to M10, 114.94 centimeters to M3 and M9, 168.91 centimeters to M4 and M8, 121.92 centimeters to M5 as well as to M7, and 93.98 centimeters to M6.

Fig 5

Measurements of normal seating positions.

A white metric measuring tape with centimeter and millimeter markings can be seen in each figure. (A) A bird’s eye view photo of 10 mannequins seated in normal positions at a table can be seen. These seating positions were designed to mimic students sitting at a cafeteria table without safety protocols. (B) All mannequins are labeled as well as the measurements of the distances from the mouth of M1 to the bodies of M2, M3, M4, M5, and M6. The shoulder-to-shoulder distance between M1 to M2 as well as M1 to M10 is displayed. The length of the table is also shown.

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 whether or not droplets could travel over the barrier, plexiglass was placed over the top of the barrier. Similar to the third experiment, the nine other surrounding mannequins were seated in normal eating positions with a barrier around M1, as shown in Fig 6B. Three 91.44 centimeter tall white boards were used as the barrier surrounding M1. One of the white boards was placed in front of M1, and the two adjacent whiteboards were placed on the sides, ending at the edge of the table. Plexiglass was applied over the top of the barrier to determine if droplets could travel over the barrier. As shown in Fig 6D, a comfortable eating space for a student was determined to be 60.96 centimeters by 38.10 centimeters while still keeping the barriers as close as possible to reduce the dispersion of droplets.

Fig 6

Measurements of normal seating positions and barrier.

A white metric measuring tape with centimeter and millimeter markings is shown in each figure. (A) A bird’s eye view photo of 10 mannequins sitting in the exact same positions as experiment 3 is shown. Three whiteboards were positioned in front of the middle mannequin on the bottom of the photo. A plate and a cup were placed on the interior of the whiteboards in front of that mannequin to better simulate the eating space. In addition, plexiglass can be seen on top of the whiteboards. (B) The ten mannequins are labeled. (C) A closer picture of the barrier in front of the mannequin simulating the cough is shown as well as a plate and a cup. There is also a metric ruler in from of the mannequin on the table as a scale. (D) The height, length, and width of the barrier is shown, and the mannequin simulating the cough is labeled M1.

In the fifth experiment, the positions of each mannequin remained constant. The two side walls of the barrier were extended off the edge of the table by 17.78 centimeters while the eating space remained the same, as shown in Fig 7. Similar to the previous experiment, the purpose of this experiment was to examine whether droplets would spread anywhere outside of the barrier.

Fig 7

Measurements of extended barrier.

The side walls of the barrier have been extended off the edge of the table. There is a white metric measuring tape with centimeter and millimeter markings that travels from the mannequin’s eating space off the edge of the table. A plate and cup are also present.

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 Fig 8A and 8B, and with a mask worn properly, as shown in Fig 8C and 8D while standing in an open space such as a hallway. These experiments were designed to test the effectiveness of a surgical mask by observing whether or not macroscopic droplets were found anywhere beyond the mask. First, table cloths were placed on the floor, covering a large area surrounding the mannequin. Then, three identical boxes were placed on a chair to mimic the height of a student. The mannequin head was then placed on top of the boxes, reaching a height of 5ft 10”. After each trial a black light was used to examine the droplets on the ground and the data was recorded. In the seventh experiment, as shown in Fig 8A and 8B, the surgical mask was placed below the nose and only covered the mannequin’s mouth. In eighth experiment, the mask was fitted around the nose and mouth of the mannequin, as shown in Fig 8C and 8D.

Fig 8

Frontal and side view of M1 wearing a mask in different positions.

A white metric measuring tape with centimeter and millimeter markings is positioned in each figure. (A) The Frontal view of M1 wearing a surgical mask improperly is displayed. (B) The side view of M1 wearing a surgical mask improperly is shown. (C) The frontal view of M1 wearing a surgical mask properly is presented. (D) The side view of M1 wearing a surgical mask properly can be seen.

Droplet sizes were measured in experiments 3, 4, and 5 with a digital fractional caliper (Ironton, China) with an accuracy of 0.013 millimeters. A total of 67 droplets were measured. The diameter of the largest droplets ranged from 0.95 mm to 3.57 mm, while the diameter of the smallest droplets ranged from 0.22 mm to 0.91 mm. The majority of the droplets were less than 1 mm in diameter.

Results

The results are separated by experiment type, and the distances of droplet spread are listed in centimeters.

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 272.42 centimeters with a range of 181.61 centimeters to 272.42 centimeters as shown in Table 1.

Table 1

(Experiment 1): Maximum distance of droplet spread traveling straightforward on the table.

	Maximum distance of droplet spread (centimeters)
Trial #1	181.61
Trial #2	204.47
Trial #3	272.42

This table shows the measurements of the maximum distance of frontal droplet spread during a simulated cough that landed on the table.

In experiment two, which was designed to determine the maximum lateral dispersion of droplets, the maximum distance of droplets traveling to the left of M1 was 200.66 centimeters with a range of 170.18 centimeters to 200.66 centimeters. Similarly, the maximum distance of droplets traveling to the right of M1 was 184.79 centimeters with a range of 158.75 centimeters to 184.79 centimeters as shown in Table 2.

Table 2

(Experiment 2): Maximum distance of droplet spread traveling laterally on the table.

	Maximum distance of droplet spread to the left of M1 (centimeters)	Maximum distance of droplet spread to the right of M1(centimeters)
Trial #1	200.66	184.79
Trial #2	176.53	132.72
Trial #3	170.18	158.75

This table displays the measurements of the maximum droplet spread travelling laterally from M1.

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 of their eating spaces, which was within at least 38.10 centimeters from the mannequin. Droplets were found on the bodies and heads of the surrounding mannequins as shown in Table 3.

Table 3

(Experiment 3): Droplet spread in normal cafeteria seating positions.

	Mannequins on which droplets were found	Droplets found on the head of the mannequin	Droplets found on the body of the mannequin	Droplets found in the eating space (within 38.10 centimeters from mannequin) of the surrounding mannequins
Trial #1	M5, M6, M7, M8, M10	M5, M6, M7	M5, M6, M7, M8, M10	M2, M3, M4, M5, M6, M7, M10
Trial #2	M2, M5, M6, M7, M8, M10	M2, M5, M6, M7, M8, M10	M6, M7, M8, M10	M2, M5, M6, M7, M8, M9, M10
Trial #3	M2, M4, M5, M6, M7, M10	M2, M4, M5, M6, M10	M2, M4, M5, M6, M7, M10	M2, M3, M4, M5, M6, M7, M9, M10

This table presents the mannequins on which droplets were found as well as the eating spaces on which droplets were found.

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 Table 4, the maximum height of droplet spread on the barrier from the fourth experiment was 90.50 centimeters, with a range of 88.70 centimeters to 90.50 centimeters. Droplets were also found on the inside of the top cover of the barrier in each trial. Droplets were most dense on the board at the height of the mouth of M1 and were found farther spread apart the higher they were found on the board. Droplets were found on the body of M2 and M10 in the third trial.

Table 4

(Experiment 4): Droplet spread with barrier use.

	Maximum height of droplet spread (centimeters)	Droplets found on the cover of the Barrier	Mannequins on which Droplets were Found with the Barrier	Droplets found on the head of the mannequin	Droplets found on the body of the mannequin	Droplets Found in the Eating space (within 38.10 centimeters from mannequin) of the Surrounding Mannequins with the Barrier
Trial #1	89.10	Yes	None	None	None	None
Trial #2	90.50	Yes	None	None	None	None
Trial #3	88.70	Yes	M2, M10	M2, M10	M2, M10	None

This table shows the maximum height of droplets that traveled on the barrier, the inside of the top cover of the barrier, the surrounding mannequins, and their eating spaces.

The fifth experiment was designed to test whether droplets were found on surfaces other than the extended barrier. As shown in Table 5, there were no droplets found on the body or head of any mannequin as well as in their eating spaces with the use of the extended barrier.

Table 5

(Experiment 5): Droplet spread with extended barrier use.

	Mannequins on which droplets were found	Droplets found in the eating space (within 38.10 centimeters from mannequin) of the surrounding mannequins
Trial #1	None	None
Trial #2	None	None
Trial #3	None	None

This table displays the effectiveness of the extended barrier in the fifth experiment.

The sixth, seventh, and eighth experiment were designed to observe the effectiveness of a surgical mask in preventing droplet spread. As shown in Table 6, droplets were found at a maximum radius of 248.92 centimeters with a range of 232.41 centimeters to 248.92 centimeters when coughing standing up without a surgical mask. In the eighth experiment, droplets were found at a maximum radius of 119.38 centimeters with a range of 99.06 centimeters to 119.38 centimeters when wearing a mask improperly. In the final experiment, no droplets found beyond the mask when the mask was worn properly. In experiment 6, 7, and 8, the results of droplet spread without a mask, with a mask worn improperly (covering only the mouth, but not the nose), and with a mask worn properly (covering both the mouth and nose) were deduced as follows. 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 6 both with the mask worn improperly and properly but not in the space or surfaces around M1 with the mask worn properly, led to the deduction that the mask prevented droplet spread.

Table 6

(Experiment 6, Experiment 7, Experiment 8): Droplet spread with and without a surgical mask.

	Maximum Radius of droplet spread without wearing a mask (centimeters)	Maximum radius of droplet spread when wearing a mask improperly (centimeters)	Maximum radius of droplet spread when wearing a mask properly (centimeters)	Droplets found on the inside surface of the mask when wearing a mask improperly and properly	Droplets found on the outside surface of the mask when wearing a mask improperly and properly
Trial #1	232.41	119.38	0	Yes	No
Trial #2	248.92	99.06	0	Yes	No
Trial #3	236.86	109.86	0	Yes	No

This table shows the spread of droplets without wearing a mask, while wearing a mask improperly and wearing a mask correctly.

Discussion

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.

It is not completely known whether respiratory macroscopic droplets can spread beyond 6 feet (2 meters) [22]. Although, a recently published study showed a simulated jet containing microscopic droplets traveling up to 12 feet [23], and another recent study show that turbulent gas clouds can travel 23–27 feet (7–8 meters) [13]. However, it is not proven at this time that microscopic respiratory jets are the predominant mechanism of disease transmission. In fact, macroscopic droplets maybe more likely the predominant mechanism involved in disease transmission since many outbreaks such the 1981 outbreak of infectious meningitis in a Texas elementary school involved students who became infected while seated within less than 3 feet 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 up to 12 feet (>2 meters) away or gas clouds travelling up to 23–27 feet (7–8 meters) away, where none of the other students were infected [26]. In the experiments contained in this manuscript, it became clear that social distancing at 6 feet (1.83 meters) 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 feet (1.83 meters) 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 much more sparse. Furthermore, when extending the sides of the barrier 17.78 centimeters offset from the table’s edge toward 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 barriers. 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.

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 [27]. In all experiments the room ventilation emanated from central ducts in the ceiling on one side of the room with the vents facing M1 and all experiments were conducted with M1 facing the ventilation ducts. Thus, the airflow was directed towards M1 and could have decreased the distance of droplet travel. However, since the airflow was not specifically measured, it could have influenced the results in other unknown ways. 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. There has been experimental evidence from other studies that the droplets generated in respiratory droplet models can vary in size and may be susceptible to evaporation [28]. 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. If the droplets did evaporate without any fluorescent residue, this may have led to an underestimation of droplet spread particularly if any droplets travelled beyond the mask in experiment 6. This could have produced a false negative finding. However, since the inside surface of the mask contained droplets and no droplets or fluorescent residue were visible on the outside of the mask or surrounding surfaces, it is less likely that substantial macroscopic droplets could have escaped the mask. 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. To the author’s knowledge, this is 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 Coronavirus during this global pandemic [29].

Conclusions

Based on the results of these experiments, social distancing at a distance of 6 feet (1.83 meters) 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.

Physical barriers should also be established in places where masks are not worn, such as cafeterias in schools to limit droplet spread. Clear barriers would seem prudent so that students would be less likely to lean back to see or to talk to other students. A barrier that was aligned with the edge of the table was not sufficient to prevent lateral droplet spread. Therefore, the barrier was extended to 17.78 centimeters beyond the edge of the table toward M1, and this prevented lateral droplet spread. In addition, droplets were consistently found on the top cover of the barrier, meaning that droplets could travel over the barrier. When the barrier extended past the edge of the table, in other words in front of the table 17.78 centimeters, it effectively prevented droplets from spreading anywhere outside the barrier. Based on these findings, it would be prudent for barriers to be constructed with this in mind.

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.

Most importantly, this series of experiments can help guide schools to establish safety guidelines and precautions as they re-open to prevent droplet spread both in the classroom and in the cafeteria setting.

11 Nov 2020

PONE-D-20-26616

“The Spread of Macroscopic Droplets from a Simulated Cough with and without the Use of Masks or Barriers”

PLOS ONE

Dear Mr Bhavsar,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Your manuscript was assessed by three external experts, whose comments are appended to this letter.

Two of the reviewers raise the important point that your submission does not engage fully with the body of existing literature on droplet dissemination and how it is affected by mask-wearing. This is important in order that the reader can understand how your findings relate to what is already known in the literature.

Reviewer 3 notes a key limitation with the methods you used that has not been discussed in your manuscript, namely that it is unclear whether the distribution of droplet sizes in your model 'cough system' is representative of those generated by humans.

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Reviewer #1: Partly

Reviewer #2: No

Reviewer #3: Partly

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Reviewer #1: N/A

Reviewer #2: No

Reviewer #3: N/A

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Reviewer #3: Yes

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Reviewer #1: Very nice effort from what appears to be a high-school student - done in the family garage with the help of family members! I commend the effort - well done! See if the journal can waive their publication fees ($1350 at present) for a high-school student.

Some suggestions to improve this paper below:

- change all distances to metric - science is metric now

- combine the smaller figures into a 4-panel figure, and the larger ones into a 3-panel figure. Make sure the Figure legends fully describe what readers are seeing - without having to refer to the main text - each Figure and its legend should stand alone. Use arrows in the figures and refer to them in the figure legend to make things clearer - sometimes it is not quite clear what the authors is saying, e.g. the overhang of the vertical barriers over the edge of the table.

- expand your reference list - before claiming a first for anything, and I wouldn't do this anyway, as by the time your paper is published, other studies may have been published already (some may already be in review), making this statement inaccurate and redundant. It does not help your study get published, and in fact some reviewers may be more critical of your paper because of you claiming this.

Some additional related studies on coughing and airflow/droplet dissemination with/without masks:

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0034818

https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1003205

https://www.pnas.org/content/115/5/1081

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2843945/

https://www.nejm.org/doi/full/10.1056/NEJMicm0904279

https://pubmed.ncbi.nlm.nih.gov/18843121/

https://pubmed.ncbi.nlm.nih.gov/32982136/

https://pubmed.ncbi.nlm.nih.gov/32304605/

https://pubmed.ncbi.nlm.nih.gov/32631450/

The limitations are good.

Try to avoid fish-eye/panoramic photos for illustration as they may distort the distances - diagrams are also useful, but it would be helpful if the author can retake all of these photos with a ruler (metric) of some sort in the image as a scale.

The cafeteria table model looks too narrow? Can the authors provide some measurements of their typical school cafeteria table to validate this model more?

Reviewer #2: This paper is very useful in demonstrating the effects of wearing masks. However, it is not clear how the results were deduced. The authors should add a section showing some intermediate results. For example, adding photographs showing aerosol, particulate or even tracers motion for scenarios with and without mask will be more convincing.

Reviewer #3: This is an admirable study performed by a high school student, and the methods and results could serve as excellent educational material in school settings. However, in my opinion, the methods are not sophisticated enough for publication in a journal with the stature of Plos One. You should cite more of the literature on the transport of droplets, as much has been published lately, e.g., from Lydia Bourouiba from MIT in JAMA 2020 and William Lindsley in 2016. A major limitation of the methods is the inability to measure the particles sizes generated by your apparatus to know whether or not they are similar to those generated by humans. One point that may seem picayune is that scientific papers should include measurements using the metric system.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

29 Dec 2020

Response to Reviewers

Reviewers’ Comments to the Author and the Author’s Responses:

Reviewer 1

1. Comment from Reviewer 1: Very nice effort from what appears to be a high-school student - done in the family garage with the help of family members! I commend the effort - well done!

Author response: Thank you!

2. Comment from Reviewer 1: See if the journal can waive their publication fees ($1350 at present) for a high-school student.

Author response: Thank you! That would be very much appreciated.

3. Comment from Reviewer 1: “Change all distances to metric.”

Author response: All measurements have been changed to the metric system.

4. Comment from Reviewer 1: “Combine the smaller figures into a 4-panel figure, and the larger ones into a 3-panel figure.”

Author response: Thank you for pointing this out. I have combined the smaller figures into 4 panel figures and the larger ones into 2 panel figures.

5. Comment from Reviewer 1: “Make sure the Figure legends fully describe what readers are seeing - without having to refer to the main text - each Figure and its legend should stand alone.”

Author response: The figure legends have been changed and fully describe the figures in the current manuscript.

6. Comment from Reviewer 1: “Use arrows in the figures and refer to them in the figure legend to make things clearer”

Author response: Arrows have been used in some of the figures to make things clearer and are referred to in the figure legend.

7. Comment from Reviewer 1: “Expand your reference list.”

Author response: The reference list has been expanded with more recent publications. The additional references that I reviewed have been included in references 3 through 15, 18 through 21, and 25.

8. Comment from Reviewer 1: “before claiming a first for anything, and I wouldn't do this anyway, as by the time your paper is published, other studies may have been published already (some may already be in review), making this statement inaccurate and redundant. It does not help your study get published, and in fact some reviewers may be more critical of your paper because of you claiming this.”

Author response: I have reviewed the literature again six months after the original manuscript was written and I am still unable to find any publications regarding cafeteria barrier use as I have described in this manuscript.

9. Comment from Reviewer 1: “The limitations are good.”

Author response: Thank you!

10. Comment from Reviewer 1: “Try to avoid fish-eye/panoramic photos for illustration as they may distort the distances – diagrams are also useful, but it would be helpful if the author can retake all of these photos with a ruler (metric) of some sort in the image as a scale.”

Author response: All panoramic photos have been eliminated, and all photos have been retaken with a metric ruler.

11. Comment from Reviewer 1: “The cafeteria table model looks too narrow? Can the authors provide some measurements of their typical school cafeteria table to validate this model more?”

Author response: The measurements of the school cafeteria have been validated and reproduced in each of the experiments as explained in lines 120 through 124.

Reviewer 2

1. Comment from Reviewer 2: “This paper is very useful in demonstrating the effects of wearing masks.”

Author response: Thank you!

2. Comment from Reviewer 2: “It is not clear how the results were deduced.”

Author response: The results were deduced by observing the fluorescent paint droplets that were ejected onto the surfaces surrounding the mannequin after the simulated cough event.

3. Comment from Reviewer 2: “The authors should add a section showing some intermediate results. For example, adding photographs showing aerosol, particulate or even tracer motion for scenarios with and without masks will be more convincing.”

Author response: I tried to capture the particle spread in motion but the particles were too small to capture by my video equipment.

Reviewer 3

1. Comment from Reviewer 3: “This is an admirable study performed by a high school student, and the methods and results could serve as excellent educational material in school settings.”

Author response: Thank you!

2. Comment from Reviewer 3: “However, in my opinion, the methods are not sophisticated enough for publication in a journal with the stature of Plos One.”

Author response: The methods of the simulated cough used in these experiments were previously used in manuscripts that have already been published in the New England Journal of Medicine, American Academy of Ophthalmology website, and the Canadian Journal of Ophthalmology in references 17, 18, and 19 in the current manuscript. Therefore, I respectfully submit that the methods that were used in this study deserve consideration for publication in Plos One.

3. Comment from Reviewer 3: “You should cite more of the literature on the transport of droplets, as much has been published lately, e.g., from Lydia Bourouiba from MIT in JAMA 2020 and William Lindsley in 2016.”

Author response: Additional scientific publications including the ones suggested in the above comment have been reviewed and cited in the current manuscript in lines 72 through 110.

4. Comment from Reviewer 3: “A major limitation of the methods is the inability to measure the particles sizes generated by your apparatus to know whether or not they are similar to those generated by humans.”

Author response: The experimental model used in the current manuscript has already been used in several other scientific published papers listed below. These have been cited as references 17, 18, and 19 in the current manuscript. In addition, the droplet sizes were measured during several experiments, and this is addressed in lines 518 to 522. Most of the droplets were less than 1 mm and that is consistent with droplet sizes that have been measured in the human cough as cited in reference 14 in the current manuscript.

1. Canelli R, Connor CW, Gonzalez M, Nozari A, Ortega R. Barrier Enclosure during Endotracheal Intubation. N Engl J Med. 2020;382(20):1957-1958. doi: 10.1056/NEJMc2007589.

2. Felfeli T, Batawi HI, Aldrees SS, Mandelcorn ED (2020, June 3). Infection Control Measures During Simulated Slit-Lamp Examination. Retrieved July 15, 2020, from https://www.aao.org/clinical-video/infection-control-measures-during-simulated-slit-l

3. Felfeli T, Batawi HI, Aldrees SS, Hatch W, Mandelcorn ED Utility of patient face masks to limit droplet spread from simulated coughs at the slit lamp. Can J Ophthalmol; 2020;55(5):e163-e165. doi: 10.1016/j.jcjo.2020.06.010.

5. Comment from Reviewer 3: “One point that may seem picayune is that scientific papers should include measurements using the metric system.”

Author response: All measurements in the current manuscript have been converted to the metric system.

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

27 Jan 2021

PONE-D-20-26616R1

The Spread of Macroscopic Droplets from a Simulated Cough with and without the Use of Masks or Barriers

PLOS ONE

Dear Dr. Bhavsar,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Mar 13 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

We look forward to receiving your revised manuscript.

Kind regards,

Zezhi Li, Ph.D., M.D.

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #2: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Reviewer #2: No

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: N/A

Reviewer #2: No

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: No

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Almost there.

Figure 2 first image - the tape measure figures are not visible properly - you cannot include any blurred images/dimensions in a scientific paper as it raise doubts about the results/interpretation - as well as the ability for others to reproduce the result accurately. Please retake this image - ensuring that the tape figures are clear and visible.

I note the concerns of one other reviewer about the method - please cite these two papers in the appropriate place to counter other similar criticisms like this:

https://royalsocietypublishing.org/doi/10.1098/rsif.2009.0388.focus

https://royalsocietypublishing.org/doi/10.1098/rsif.2009.0311.focus

Reviewer #2: Appears not yet revised thoroughly following:

This paper is very useful in demonstrating the effects of wearing marks. However, it is not clear how the results were deduced. The authors should add a section showing some intermediate results. For example, adding photographs showing aerosol, particulate or even tracers motion for scenarios with and without mask will be more convincing.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: Yes: Julian W Tang

Reviewer #2: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

14 Feb 2021

Response to Reviewers

Dear Dr. Li,

Thank you for providing me the opportunity to submit a revised version of the manuscript. “The Spread of Macroscopic Droplets from a Simulated Cough with and without the Use of Masks or Barriers” for publication in the journal of the Public Library of Science. I appreciate the time and effort that you and the reviewers dedicated to address the limitations in the paper and provide feedback. All of the changes suggested by the reviewers have been updated and addressed in the revised manuscript.

Reviewers’ Comments to the Authors:

Reviewer 1

Comment from Reviewer 1: “Almost there.”

Author response: Thank you!

Comment from Reviewer 1: “Figure 2 first image - the tape measure figures are not visible properly - you cannot include any blurred images/dimensions in a scientific paper as it raise doubts about the results/interpretation - as well as the ability for others to reproduce the result accurately. Please retake this image - ensuring that the tape figures are clear and visible.”

Author response: The first image in Figure 2 has been retaken so that the measuring tape is clear and visible.

Comment from Reviewer 1: “I note the concerns of one other reviewer about the method - please cite these two papers in the appropriate place to counter other similar criticisms like this.”

Author response: The method of how the results were deduced regarding the experiments with masks and the associated shortcomings have been addressed in lines 294 to 300, 339 to 344, and 347 to 359. References 27 and 28 have been revised with the reviewer’s suggested new references added to the manuscript.

Reviewer 2

Comment from Reviewer 2: “This paper is very useful in demonstrating the effects of wearing masks.”

Author response: Thank you!

Comment from Reviewer 2: “It is not clear how the results were deduced.”

Author response: The method of how the results were deduced regarding the experiments with masks and the associated shortcomings have been addressed in lines 294 to 300.

Comment from Reviewer 2: “The authors should add a section showing some intermediate results. For example, adding photographs showing aerosol, particulate or even tracer motion for scenarios with and without masks will be more convincing.”

Author response: I tried to capture the particle spread in motion but the particles were too small to capture by my video equipment. I did add an explanation of how the methods were deduced in lines 294 to 300, and I added columns to table 6 explaining that droplets were present on the inside of the mask and not on the outside of the mask during the simulations.

Sincerely,

Atreyus A. Bhavsar

Submitted filename: Response to Reviewers.docx

Click here for additional data file.

3 Mar 2021

PONE-D-20-26616R2

The Spread of Macroscopic Droplets from a Simulated Cough with and without the Use of Masks or Barriers

PLOS ONE

Dear Dr. Bhavsar,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Apr 17 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

We look forward to receiving your revised manuscript.

Kind regards,

Zezhi Li, Ph.D., M.D.

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: No

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: No

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: No

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The author has responded satisfactorily to my comments - congratulations! For interest - some links to the use of barriers and masks in schools in Southeast Asia - where they have dealt with the COVID-19 pandemic much more effectively:

Thailand:

https://www.google.co.uk/amp/s/metro.co.uk/2020/08/10/school-children-put-boxes-return-class-lockdown-13108120/amp/

https://www.google.co.uk/amp/s/www.dailymail.co.uk/news/article-8611385/amp/Thai-kindergartners-sealed-perspex-boxes-playtime-fight-against-coronavirus.html

Hong Kong:

https://www.google.co.uk/amp/s/amp.scmp.com/news/hong-kong/education/article/3084267/masks-while-singing-no-basketball-and-recess-inside-hong

Taiwan:

https://www.google.co.uk/amp/s/www.cbc.ca/amp/1.5505031

Vietnam:

https://www.google.co.uk/amp/s/www.vox.com/platform/amp/21270817/coronavirus-schools-reopen-germany-vietnam-new-zealand

For interest - here are some links showing actual barriers used in sine schools in Southeast Asia - where they have managed the COVID-19 pandemic much more effectively:

Reviewer #2: Appears that the following have not yet been revised thoroughly:

This paper is very useful in demonstrating the effects of wearing masks. However, it is not clear how the results were deduced. The authors should add a section to show some intermediate results. For example, adding photographs showing the aerosol, particulate or even tracers motion for scenarios with and without mask will be more convincing.

1. Not clear what have been revised, photographs are still not too clear.

2. There are articles published recently using high-speed camera with higher quality photographs.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: Yes: Julian W Tang

Reviewer #2: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

15 Mar 2021

Response to Reviewers

Dear Academic Editor,

I received the response dated March 3 regarding my manuscript submission. In my prior responses to the reviewers and my revisions submitted on February 14, I have responded to each of the reviewers' comments and made all the requested and appropriate revisions to the manuscript.

Sincerely,

Atreyus A. Bhavsar

Reviewers’ Comments to the Authors:

Reviewer 1

1. Comment from Reviewer 1: “The author has responded satisfactorily to my comments - congratulations!”

Author response: Thank you!

2. Comment from Reviewer 1: “For interest - some links to the use of barriers and masks in schools in Southeast Asia - where they have dealt with the COVID-19 pandemic much more effectively”

Author response: Thank you!

Reviewer 2

1. Comment from Reviewer 2: “This paper is very useful in demonstrating the effects of wearing masks.”

Author response: Thank you!

2. Comment from Reviewer 2: “It is not clear how the results were deduced.”

Author response: The method of how the results were deduced regarding the experiments with masks and the associated shortcomings have previously been addressed in lines 294 to 300 during the prior round of revisions.

3. Comment from Reviewer 2: “The authors should add a section showing some intermediate results. For example, adding photographs showing aerosol, particulate or even tracer motion for scenarios with and without masks will be more convincing.”

Author response: I tried to capture the particle spread in motion but the particles were too small to capture by my video equipment. I previously added an explanation of how the methods were deduced in lines 294 to 300, and I added columns to table 6 explaining that droplets were present on the inside of the mask and not on the outside of the mask during the simulations.

4. Comment from Reviewer 2: “Not clear what have been revised, photographs are still not too clear.”

Author response: The revisions are clearly listed in my previous response to reviewers in lines 294-300. In the last set of revisions, Figure 2.A was the only figure that was requested to be revised and this was revised to show the measuring tape in the background.

5. Comment from Reviewer 2: “There are articles published recently using high-speed camera with higher quality photographs.”

Author response: I do not have access to a high-speed camera, and the images that have been submitted have already been approved by both Reviewer 1 and Reviewer 2 in prior revisions of this manuscript.

Submitted filename: Response to Reviewers..docx

Click here for additional data file.

24 Mar 2021

PONE-D-20-26616R3

The Spread of Macroscopic Droplets from a Simulated Cough with and without the Use of Masks or Barriers

PLOS ONE

Dear Dr. Bhavsar,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

One of the reviewer's comments should be carefully addressed.

Please submit your revised manuscript by May 08 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Zezhi Li, Ph.D., M.D.

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #2: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #2: No

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: No

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

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Reviewer #2: No

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Reviewer #2: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #2: Without clear photographs as said, what is the value of this paper ?

However, in order not to cause too much trouble, perhaps the authors can improve the paper by trying the following, if they do not have access to a high-speed camera :

1. Draw better diagrams on what they try to present, and put those diagrams next to the unclear photographs.

2. Compare with other references showing clear photographs.

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Reviewer #2: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

31 Mar 2021

Response to Reviewers

Dear Dr. Li,

Thank you for providing me the opportunity to submit a revised version of the manuscript. “The Spread of Macroscopic Droplets from a Simulated Cough with and without the Use of Masks or Barriers” for publication in the journal of the Public Library of Science. I appreciate the time and effort that you and the reviewer dedicated to address the limitations in the paper and provide feedback. All of the changes suggested by the reviewers have been addressed below.

Reviewer’s Comments to the Author:

Reviewer 2

1. Comment from Reviewer 2: “Without clear photographs as said, what is the value of this paper ? However, in order not to cause too much trouble, perhaps the authors can improve the paper by trying the following, if they do not have access to a high-speed camera : 1. Draw better diagrams on what they try to present, and put those diagrams next to the unclear photographs. 2. Compare with other references showing clear photographs.”

Author response: I sent all the native tiff figure files to the academic editor and he responded as follows:

“Dear Dr. Bhavsar,

The pictures you send to me are very clear. Thank great! You can submit these pictures as supplementary files if you possible.

Kind regards,

Zezhi Li

Academic Editor

PLOS ONE”

The editorial office also wrote the following to explain that the built PDF images are of low resolution and the original figure files that I uploaded were of high resolution:

“Dear Dr. Li,

Thank you for acting as Academic Editor for this submission to PLOS ONE. Further to your previous correspondence with the Corresponding Author, we have received the email below along with figures attached.

Unfortunately, we do sometimes find that the figure quality in the PDF for review can be poor, but please be assured that the submission PDF is for reviewing purposes only and does not reflect the appearance of the final publication. Should the manuscript be accepted, the figures will be typeset at the resolution of the original submitted figures.

I have attached a copy of the Revision 3 PDF for review to this email and you can access to the original source files via the blue download link in the top right corner of the PDF rendering of the figure.

If I can be of any assistance in forwarding a response to the Corresponding Author on your behalf, please do let me know and I would be happy to help. If you respond directly to the corresponding author, please could I ask that you copy us in at - plosone@plos.org.

Please do not hesitate to contact me if you have any queries, or if I can be of any assistance at all. Many thanks again for your time and efforts with this manuscript.

Kind regards,

Noelle Noelle Gibbs

Editorial Office”

Therefore, the academic editor, Zezhi Li, has asked me to submit the manuscript again without needing any additional revisions to the figures since the original figures submitted are of high resolution.

Sincerely,

Atreyus A. Bhavsar

Submitted filename: Response to Reviewers .docx

Click here for additional data file.

5 Apr 2021

The Spread of Macroscopic Droplets from a Simulated Cough with and without the Use of Masks or Barriers

PONE-D-20-26616R4

Dear Dr. Bhavsar,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Zezhi Li, Ph.D., M.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

12 Apr 2021

PONE-D-20-26616R4

The Spread of Macroscopic Droplets from a Simulated Cough with and without the Use of Masks or Barriers

Dear Dr. Bhavsar:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Zezhi Li

Academic Editor

PLOS ONE