Aerosolized Transmission

This forum is to discuss general things concerning TSOI.
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Re: Aerosolized Transmission

Post by trader32176 »

Reducing aerosol transmission could help tackle COVID-19 pandemic

12/8/20 ... demic.aspx

Aerosols and their spread play an essential role in the transmission of COVID-19. However, the risk of transmission could be significantly reduced if more could be done to reduce indoor airborne viruses. The Working committee particulate matter (AAF) has therefore issued an statement with concrete recommendations. These include window ventilation, exhaust ventilation, air purification systems and CO2 measuring devices for indoor areas such as classrooms or transportation, and the increased use of N95 and FFP2 masks.

These countermeasures could help in the short term to better contain the corona pandemic, especially in winter, until vaccination is effective on a large scale. They could also help in the long term to better control infections such as seasonal fluor even other pandemics in the future.

The German Working committee particulate matter (AAF) brings together experts from the fields of engineering, chemistry, physics, biology, meteorology and medicine, who are organised in the professional associations ProcessNet (DECHEMA/ VDI-GVC), Gesellschaft Deutscher Chemiker (GDCh) and VDI/DIN Commission Reinhaltung der Luft (KRdL). In its autumn meeting, the AAF discussed the role of aerosol particles in the spread of the SARS-CoV2 viruses and prepared a statement on this topic.

On the basis of their expertise, the authors describe in the now published statement different aerosol types with regard to their formation, range, residence time in the air and derive recommendations for protection by various measures. The authors expressly support the current recommendations of the Robert Koch Institute (RKI), but suggest that even more should be done to reduce the number of viruses in indoor air.

The Working committee particulate matter (AAF) advises strict application of the recommendations based on the active aerosol propagation path: masks (especially the use of N95 and FFP2 masks) are helpful and necessary, ventilation is a good immediate measure and suitable air purifiers should be used.

Furthermore, the Panel concludes that more attention should be paid to the type of ventilation in addition to the measures already taken: Especially the smaller aerosol particles rise with the warm air we breathe and then spread below the ceiling. The experts on the working committee therefore recommend that in ventilation systems, care should be taken to ensure that fresh air is not supplied from top to bottom, as this leads to turbulence between the fresh air and the air we breathe and viruses can then float in the room air for longer. Ceiling fans, which are counterproductive in the current COVID 19 pandemic, would also contribute to this. Instead, care should be taken to ensure that air is actually extracted upwards. In the future, a reversal of the air supply and extraction in aircraft or public transport could help.

The panel of experts also advises to install ventilation and especially overhead exhaust suction systems in many areas at short notice, especially in classrooms or in the catering industry. Monitoring the CO2 concentration is a suitable indicator of how well the ventilation works. For cultural facilities, too, monitoring the CO2 content and thus the indoor air could later provide opportunities for normalising operation. In the Länder, funds should be made available so that ventilation, extraction, air purification systems and CO2 measuring devices can be installed in school classes. At the local level, it would be helpful if administrative regulations were relaxed and school managements were given more freedom of action. If these measures were implemented consistently, about 90 percent of all potentially viral aerosols could be removed from classrooms.

" We clearly see the human and technical effort involved in the short and medium term, but we are convinced that the appropriate consideration of the virus spread via the aerosol path can lead to a short-term and also sustainable containment of the current incidence of infection. Such investments would also be beneficial for later, for example for the air quality in classrooms."

- Prof. Hartmut Herrmann, Leibniz Institute for Tropospheric Research (TROPOS), Chairman of the Working Committee on Particulate Matter (AAF)

Herrmann also contributes to recommendations by an international group of aerosol researchers) and via the VDI/DIN Commission on Air Pollution Control (KRdL), which were incorporated into specific recommendations for German conditions. Even if the World Health Organization (WHO) still pays too little attention to this, experts have long been convinced that aerosols, i.e. tiny suspended particles in the air, contribute strongly to the spread of the SARS-CoV2 viruses. "We are aware that the technical implementation of more efficient ventilation measures is probably one of the most demanding measures in the current situation in Germany. However, protection against infection from virus-contaminated aerosol particles in indoor rooms and means of transport through improved ventilation technology is particularly important in the cold winter months in order to avoid corona superspreader events", emphasizes Prof. Peter Wiesen from the Bergische Universität Wuppertal, who is one of the authors of the statement.

Protective measures against the spread of SARS-CoV-2 via indoor aerosols currently pose major challenges for many sectors of society. The risk of infection is particularly high in hospitals and nursing homes because infected and healthy people can stay sometimes in the same room for long periods of time.

According to media reports, COVID-19 infections are already reported in almost one tenth of the 12,000 old people's homes and nursing homes in Germany. Homes are now also considered as hotspot for the spread of the virus among new infections in Saxony. An international group of aerosol researchers proposes therefore a variety of measures to prevent the spread of the virus in hospitals and nursing homes. It is particularly important to develop an appropriate strategy to protect healthcare workers from airborne transmission.

Their recommendations in the International Journal of Environmental Research and Public Health include regular ventilation, controlling fresh air consumption via CO2 monitor and using humidifiers to keep the relative humidity indoors at 40 to 60 percent. If it is not possible to ventilate sufficiently, the use of portable air purifiers are also advisable.

In addition to the recommendations already made by the Robert Koch Institute and the National Academy of Sciences Leopoldina in Germany, the Working Committee sees an opportunity to take additional protective measures to contain the Covid-19 pandemic, initially in the short term, until a vaccine has reached a really broad section of the population. In addition, these measures could in the future also help to reduce infections such as seasonal influenza, which are spread through the air.


Leibniz Institute for Tropospheric Research (TROPOS)

Journal reference:

Ahlawat, A., et al. (2020) Preventing Airborne Transmission of SARS-CoV-2 in Hospitals and Nursing Homes. International Journal of Environmental Research and Public Health.
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Re: Aerosolized Transmission

Post by trader32176 »

Risk of COVID-19 transmission increases when walking through corridors

12/15/20 ... idors.aspx

New research has found that COVID-19 infected individuals breathe out water droplets laden with the virus that can form into long streams that trail behind them when walking through narrow corridors. These findings have significant implications on the guidelines in place to protect people from airborne transmission.

Those infected with COVID-19 create a trail of infected droplets

A team of scientists at the Chinese Academy of Sciences have researched how droplets are dispersed in different environments to understand more about how COVID-19 is transmitted. While countries across the globe have enforced some kind of social distancing restrictions for most of the year, scientists continue to investigate how the virus is transmitted to control the pandemic, which is still seeing hundreds of thousands of new cases reported daily.

Published this month in the journal Physics of Fluids, from the American Institute of Physics, the paper published by the Chinese team reveals how they used computer simulations to predict patterns of airflow and droplet dispersal in different scenarios. The team concludes how the shape and size of the space influence these patterns.

The study’s findings highlight how walking quickly behind an infected adult in a narrow corridor is a scenario that increases the risk of transmission, particularly for children who are closer to the height of the trail of droplets as they fall through the air.

Narrow corridors particularly risky, especially for children

Previous researchers had developed the stimulation technique used in the current study to investigate how objects such as air conditioners, glass barriers, toilets, and windows, impact the airflow patterns and ultimately, how the virus is transmitted through the air. These earlier studies focused on airflow patterns in larger, open indoor spaces. Until now, airflow patterns in tighter spaces had not been studied concerning COVID-19 transmission.

The team, based in China, has found that when a person coughs while walking through a corridor, they introduce water droplets into the air that form a trail, traveling around the person’s body as water would move around a speeding boat.

The team referred to this pattern of water droplets as a “re-circulation bubble”, which then forms a trail that lingers behind them as they walk, following them at roughly waist height. This trail of droplets, if produced by someone infected with COVID-19, puts those walking behind the person at an increased risk of contracting the virus.

Further to this, the team found that “flow patterns we found are strongly related to the shape of the human body”, one of the paper’s authors, Xiaolei Yang, continued, “at 2 meters downstream, the wake is almost negligible at mouth height and leg height but is still visible at waist height.”

After determining the airflow patterns, the researchers were able to model the dispersal of the droplets, following them from their origin at the mouth. They found that the shape of the environment had a dramatic effect on droplet dispersal.

They concluded that the droplets dispersed in one of two modes. The first mode seeing the droplets move from the mouth to float steadily behind them, forming a bubble of droplets that hang far behind the person. The second mode involves the droplets attaching themself closely to the person’s back, floating behind them like a tail as they move.

" for the detached mode, the droplet concentration is much higher than for the attached mode, five seconds after a cough, this poses a great challenge in determining a safe social distance in places like a very narrow corridor, where a person may inhale viral droplets even if the patient is far in front of him or her.”


The team concluded that children were at particular risk of this type of transmission, given that in both modes, the droplets move to what is around mouth level for children. The findings of this study will likely be invaluable to the development of more effective social distancing guidelines.
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Re: Aerosolized Transmission

Post by trader32176 »

Slower drill rotation during dental procedures can reduce COVID-19 spread

12/17/20 ... pread.aspx

Dental procedures can pose a high risk of viral transmission because the tools that are used often produce aerosols, which can contain high numbers SARS-CoV-2 virions, copies of the virus causing COVID-19.

The aerosols are generated when saliva mixes with water and air streams used in dental procedures. As a result, access to routine dentistry continues to be limited during the current COVID-19 pandemic.

Dental practices, which are now back in operation, have had to introduce new room decontamination processes and personal protective equipment measures which have dramatically reduced the number of patients that can be treated in a single day.

In particular, dentists need to leave long intervals between treatments, leaving rooms unoccupied to allow aerosols to dissipate. This is limiting patient access and challenging financial feasibility for many dental practices worldwide.

Now, researchers at Imperial College London and King's College London have measured and analysed aerosol generation during dental procedures
and suggested changes to prevent contamination in the first place to improve safety for both patients and the dental practice workforce.

They suggest that dentists avoid using dental drills that use a mixture of air and water as the abrasion coolants, and carefully select and control drill rotation speeds for those instruments that only use water as a coolant. Parameters have been identified that would allow some procedures such as dental fillings to be provided whilst producing 60 times fewer aerosol droplets than conventional instrumentation.

Lead author Dr Antonis Sergis of Imperial's Department of Mechanical Engineering said: "Aerosols are a known transmission route for the virus behind COVID-19, so, with our colleagues at King's, we have tested suggested solutions that reduce the amount of aerosols produced in the first place. These could help reduce the risk of transmission during dental procedures."

Co-author Professor Owen Addison of King's College London's Faculty of Dentistry, Oral & Craniofacial Sciences said:

" This important work describes the basic mechanisms that lead to the features of dental aerosols that we currently consider to be high risk. This has enabled us to choose drill parameters to keep our patients and the dental team safe at this difficult time. Although we cannot provide every procedure, because slowing our drills is much less efficient, we now have the basis to do more than we have done in the last 6 months."

The results are published today in Journal of Dental Research and are already being included as evidence in guides for dental practices in the UK during the pandemic. The collaborative research used the engineering expertise at Imperial and clinical expertise at King's College London's Faculty of Dentistry, Oral & Craniofacial Sciences.

The researchers used dental clinical rooms at Guy's Hospital in London to test how aerosols are generated during procedures such as decay removal, applying and polishing fillings and adjusting prostheses. They measured the aerosol generation using high speed cameras and lasers. They then used these findings to suggest modifications.

They found that using air turbine drill types, which are the most common type of dental drill, creates dense clouds of aerosol droplets that spread as fast as 12 metres per second and can quickly contaminate an entire treatment room. Just one milliliter of saliva from infected patients contains up to 120 million copies of the virus, each having the capacity to infect.

They tested a different type of drill, known as high torque electric micromotor, with and without the use of water and air streams. They found that using this drill type at low speeds of less than 100,000 rpm without air streams produced 60 times fewer droplets than air turbine drill types.

In addition, they found that aerosol concentration and spread within a room is dependent on the positioning of the patient, presence of ventilation systems, and the room's size and geometry. It is also influenced by the initial direction and speed of the aerosol itself, which can be affected by the type of cutting instrument (burr), and the amount and type of cooling water used.

The researchers say that by understanding how to reduce the amount of aerosol generated in the first place, their suggestions could help dentists practice more and help patients get the treatment they need.
They also note that patients should still not attend dental appointments if they have symptoms of COVID-19.

Professor Owen Addison from King's said: "Because of the COVID-19 pandemic, dentistry has become a high-risk practice - but the need for treatments hasn't gone away. Our suggestions could help begin to open up dentistry to patients once again."

Their suggestions have been included in the evidence appraisal in dentistry document entitled "Rapid Review of Aerosol Generating Procedures in Dentistry", published by the Scottish Dental Clinical Effectiveness Programme (SDCEP). The results from the study have also been considered by an expert task force convened by the Faculty of General Dental Practice (FGDP (UK)) and the College of General Dentistry and published in their guide entitled "Implications of Covid-19 for the safe management of general dental practice."

Co-author Professor Yannis Hardalupas of Imperial's Department of Mechanical Engineering said:

" The impact of the results is significant. For example, the risk categorisation for dental procedures included in the FGDP (UK) document was certainly influenced by our work."

The team's research is ongoing. They are currently better assessing the risk of infection by quantifying the amount of saliva mixed into the generated aerosols by dental instruments.


Imperial College London
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Re: Aerosolized Transmission

Post by trader32176 »

A hand-held device that measures aerosols could help prevent spread of COVID-19

12/22/20 ... ID-19.aspx

Researchers have confirmed the efficacy of a portable particle detector at calculating the concentration of aerosols in public spaces. Hand-held devices may be vital in the fight against the COVID-19 pandemic, given the important role that aerosols play in the transmission of the virus.

Aerosol transmission of COVID-19

The latest research has uncovered the fundamental role that aerosols play in the transmission of the COVID-19 virus. Aerosols, produced when humans respire and release water droplets into the immediate environment. These droplets can measure less than 60 μm and can be laden with the COVID-19 virus if expelled into the air by an infected person.

Data has shown that aerosols can persist in public spaces and that the duration that they can linger, along with the concentrations they accumulate in, contribute to the risk of transmission of the virus in different environments.

Obtaining a clearer understanding of what impacts aerosol duration and persistence will help scientists make recommendations on how best to manage shared spaces to prevent the spread of COVID-19.

However, until now, it has been difficult to accurately measure aerosol concentrations, with specialized staff and equipment required to carry out the task. It was this limitation that inspired a team at the Cardiology Centers of the Netherlands and the University of Amsterdam to establish an accurate, portable, and simple to use method of measuring aerosol concentration.

The researchers investigated the efficacy of the Fluke 985, at determining the concentration of aerosols in public spaces. The researchers believe hand-held devices will be useful in determining how suggested measures impact the concentration of potentially virus-laden particles in the environment, thus measuring their potential efficacy at preventing COVID-19 transmission.

Eliminating background dust from aerosol measurements

In a paper published this month in the journal Physics of Fluids, the team describes developed their method using a hand-held particle counter that is capable of overcoming the challenge of separating background dust particles that are prevalent in shared spaces. Previously, it had been difficult for equipment to distinguish particles of interest, such as water droplets produced by breathing, speaking, sneezing, or coughing, from irrelevant dust particles.

The researchers recognized that particles of dust differ in size from that of aerosols. This difference allowed the University of Amsterdam scientists to subtract the signal produced by dust from the signal produced by aerosols. To do this, the team measured the dust for an extended period and monitored how the signal changed as they added aerosols into the mix.

One of the study’s authors, Daniel Bonn, summarizes how the overcame the problem of dust interfering with the signal, “there's a lot of fine dust, so we can't measure aerosols in that range, but there is a reasonably sized range where you can detect the aerosols.” Bonn and the team compared the aerosol concentration calculated via this method to that of laboratory-based techniques, they found that the results were identical.

The study’s findings demonstrate that the Fluke 985, developed to monitor the air and dust quality in clean rooms, can determine the aerosol concentration in a public space. Bonn highlights that the findings aren’t likely to be specific to the Fluke 985, and it is likely that other handheld devices may be just as effective.

While technology cannot measure or detect the presence of infected particles, it provides a useful tool to help scientists understand how particles build up and linger in shared spaces. This data is vital to understanding how virus-laden particles spread and what risk they pose to those using the shared space.

Hand-held devices will likely help to confirm the efficacy of strategies to prevent transmission of COVID-19, such as demonstrating how ventilation can reduce aerosol concentration, as well as help to develop new strategies.

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Re: Aerosolized Transmission

Post by trader32176 »

New portable shield prevents spread of saliva and aerosols generated during dental procedures

12/21/20 ... dures.aspx

Dental treatments are performed at close proximity to the mouths and noses of the patients, and the procedures are often related to the generation of aerosols as well as handling of oral fluids and blood. This puts dentists at a high risk of exposure to COVID-19, and other critical infectious diseases.

Now, researchers from the National University of Singapore (NUS) have invented a portable tent-like shield to prevent the spread of saliva and aerosols generated during dental procedures. The Dental Droplet and Aerosol Reducing Tent (Dental DART) can be placed around the patient's head to serve as a barrier to protect dentists, nurses and patients from direct and indirect exposure to infectious diseases such COVID-19.

In addition, the Dental DART limits the spread of aerosols onto environmental surfaces, decreasing pathogen availability and potential cross-contamination.

This device is an adaptation of DART, an earlier NUS innovation that protects healthcare workers when they perform procedures that generate droplets and aerosols, such as intubation and extubation.

" The Dental DART is a design evolution, and has been prepared to protect dentists and their patients from potential infectious agents present in the aerosols that are generated during dental procedures."

- Freddy Boey, Study Lead Researcher, Professor, and Deputy President (Innovation & Enterprise), National University of Singapore

How the Dental DART works

The Dental DART is a clear tented shield with a depth of 54 centimetres at its base, and is 64 centimetres high. Its width is adjustable to between 60 and 70 centimetres, to suit dental chairs of different sizes. It comes with three access ports, for dentists and nurses to reach in and safely perform dental procedures.

The tent is attached to vacuum pumps that are available on dental chairs. This system safely removes the contaminated air from the tent, directing it to the scavenging system. This decreases the amount of contaminated materials in contact with the clinician's hands and arms, and instruments.

"It took us three months to come up with an ideal model. We had to design 'universal hinges' that allow for the device to suit all models of dental chairs, derive a proper design that allows foldability, as well as incorporate suitable positions for the access ports," shared Mr Sudarshan Anantharaman who is from the NUS Industry Liaison Office, and a co-inventor of this innovation.

The Dental DART has been tested in a clinical setting by measuring the bacterial content on the surface of the dental chair light, and on the face shield worn by the dentist. The tests were conducted before and after scaling procedures – which are known to significantly increase air contamination – were performed.

The results showed that was no increase in the number of viable bacteria on these surfaces after the treatment with the use of the Dental DART. On the other hand, without the use of the tent, there was a significant increase in contamination by 14 times.

"Personal protective equipment, or PPE, can be infected after being exposed to aerosols from dental procedures. The use of the Dental DART can decrease the PPE exposure to aerosols and prevent further environmental contamination at the time the clinicians remove theirs arms, hands, and instruments from the tent," said Associate Professor Vinicius Rosa, who is from the NUS Faculty of Dentistry and a co-inventor of the device.

Safer visits to the dentist

The US Bureau of Labour Statistics has categorised dentists within the class of workers with the highest high risk of COVID-19 contamination due to both high proximity to individuals and exposure to disease. Furthermore, other infectious agents responsible for pneumonitis, influenza, hepatitis, skin and eye infections, may also be transmitted during routine dental procedures.

"Dentistry is an essential service and it has suffered tremendously since the beginning of this pandemic. Many dental service providers in Singapore have imposed a complete ban in aerosol-generating procedures during the COVID-19 outbreak. While imposing such extreme measure is understandable, it has also left thousands of people without proper treatment. Our Dental DART can help provide a safer environment in the dental clinic setting, and decrease the anxiety and psychological distresses imposed by the COVID-19 pandemic on all parties involved," explained co-inventor of the device Professor Mandeep Singh Duggal, who is from the NUS Faculty of Dentistry.

Deployment in dental clinics in Singapore and globally

The four NUS researchers have filed a patent for the design of the Dental DART. They are looking to collaborate with healthcare and industry partners to make this device available to dentists in Singapore and around the world.
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Re: Aerosolized Transmission

Post by trader32176 »

Nasolaryngoscopy hood effectively reduces aerosol exposures to patients

12/23/20 ... ients.aspx

The COVID-19 pandemic has continued to cause dramatic shifts in the practice of otolaryngology. Even with standard precautions such as physical distancing and wearing personal protective equipment, aerosol-generating procedures such as nasolaryngoscopy (a commonly performed in-office procedure in which a soft, flexible fiber-scope is passed through the nose and into the throat) and intranasal instrumentation were determined to carry a risk of potential transmission if not adequately protected.

In an effort to mitigate exposure to these airborne particles, researchers from Boston University School of Medicine (BUSM) designed and tested a prototype nasolaryngoscopy hood, worn by the patient that offers safe and effective protection in reducing aerosols exposures.

In order to test the efficacy of the hood, a particle counter was used to calculate the average number of 0.3-mm particles/L detected during various clinical scenarios that included sneezing, nasolaryngoscopy, sneezing during nasolaryngoscopy and topical lidocaine spray administration. Experiments were repeated to compare the effectiveness of the hood versus no protection.

When no patient barrier (hood or mask) was used, a significant increase in aerosols was detected during sneezing, sneezing during nasolaryngoscopy and topical spray administration. With the hood was in place, the level of aerosols returned to baseline levels in each scenario.

" This simple intervention allows patients to undergo routine flexible nasal laryngoscopy, even with topical lidocaine spray administration, with less risk to the provider. If a patient begins to sneeze during the examination, our data suggest that providers will remain protected through the use of the hood."

- Christopher Brook, MD, Corresponding Author, Assistant Professor of Otolaryngology--Head and Neck Surgery, BUSM

While this study evaluated the efficacy of the hood in the setting of a routine nasolaryngoscopy in reducing aerosol spread, there are other possible applications but also one major barrier to overcome. "For clinical use, either the hood would need to be mass produced to allow for single use, or a safe and effective protocol of cleaning and reusing each hood would need to be established," said Brook who also is an otolaryngologist at Boston Medical Center.

These findings appear online in the journal Otolaryngology-Head and Neck Surgery.


Boston University School of Medicine

Journal reference:

Plocienniczak, M.J., et al. (2020) Evaluating a Prototype Nasolaryngoscopy Hood During Aerosol-Generating Procedures in Otolaryngology. Otolaryngology-Head and Neck Surgery.
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Re: Aerosolized Transmission

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Schlieren techniques demonstrate patterns of exhaled air spread from wind instruments and singers

1/10/21 ... ngers.aspx

The airborne spread of pathogens has assumed great importance in the public eye following the onset of the coronavirus disease 2019 (COVID-19 pandemic). In an interesting new research paper published recently on the bioRxiv* preprint server, scientists describe the dispersal of exhaled air, potentially infected, from singers and those playing wind instruments, using Schlieren techniques, a visual process that is used to photograph the flow of fluids of varying density. This could help assess measures to assess the actual spread of infectious droplets or aerosols in such situations.

It is now known that both droplets and aerosols, with a size of > 5 µm and < 5 µm, respectively, carry the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can spread outwards depending on their size. Heavier droplets, about 100 µm in size, travel only a few seconds before they fall to the ground, reaching about 1.5 m from the source. However, the smaller particles in aerosols can remain suspended far longer in the air.

Earlier, several studies have concluded that the spread of such particles is almost nil at 0.5 m from the mouth of a professional singer, as indicated by the presence of only minute disturbances observed at a candle flame placed at this distance from the source of exhaled air. Later, it was observed that exhalation of air is much more forcible during professional singing rather than during speaking or breathing.

With wind instruments, the pattern of air escape is similar to that of singing, with the distance of spread being determined by the speed at which air escapes from the mouth or instrument and the outlet diameter.

The current study applies flow visualization techniques and anemometry to investigate the dispersal of exhaled air in terms of the pattern of spread and the velocity at which the air escapes. The scientists used two methods to observe the flow, namely, schlieren imaging using a schlieren mirror and background-oriented schlieren (BOS).

Schlieren refers to a method of photography applied to the visualization of flows of varying density by exploiting the bending or refraction of light rays when they pass across an interface separating two substances of different densities.

The advantages of these techniques are the ability to observe density gradients in transparent media, due to variations in temperature or pressure, without distorting the flow field. The measurement field of schlieren imaging is restricted by the mirror size, that is, 100 cm. To correctly visualize the spread of exhaled air beyond these limits, BOS was used.

The breathing air is warmer and more humid than the surrounding air, leading to gradients that can be captured by these techniques. The researchers looked at woodwind instruments, which release air in an initial laminar pattern followed by turbulence, and finally mixing with the surrounding room air. With singers, the air spreads most as the tone production begins and is highest when singing consonants or when precise articulation is required.

The researchers observe that both the distance to which exhaled air spreads and the angle at which air escapes are both different with the instrument and player, or singer.

Woodwind instruments

With woodwind instruments, air escapes from the bell, the tone holes, and is blown over (flutes) or leaks near the mouthpiece (with the oboe or bassoon). Playing the oboe or bassoon requires intermittent exhalation through the mouth and nose as well, since all the air cannot escape from the tone holes. The air travels fastest when high pitches are used, but also during intermittent exhalation. With the latter, the velocity decreases steadily thereafter.

Convective flow may also occur, accounting for air movements of about 0.02 m/s at 85 cm away from the bell. This is the farthest sensor. With the most proximal sensor, the highest velocity is observed at 45 seconds, corresponding to very transient jets produced by large emissions of breathing air.

Air escapes from the bell over much shorter distances relative to the air that leaks from the instrument at various points, or during intermittent blowing, and other practices of sound production. Air leaks can travel about 60 cm into the room from the intermittent exhalation of air through the mouth and nose between two phrases. However, it moves to within 30 cm when playing various notes. At high pitches, air hardly escapes from the bassoon bell, while the greatest velocity of airflow from the bell is at low notes. Since most tone holes are uncovered at high notes, these produce maximal airflow from these holes.

The air escaping from the bell travels different distances depending on the bore width and the breathing pressure at the moment of playing.

Brass instruments

With brass instruments, the schlieren imaging shows that with most of these instruments, the escaping air from the bell is very turbulent because of the bigger diameter of the bell. The air blown into the mouthpiece blows into the bell.

The breathing air either travels up because of natural convection or mingles with the room air. The factors that decide the shape and the distance of the air that escapes from the bell include the musician’s physique and blowing technique, and the angle of the instrument to the mouth. The distances were measured from the bell, the mouth, or the mouthpiece. Breathing air goes out from the bell to about 25 cm at low pitches and a little more at high pitches. Air can leak from the mouthpiece when the player’s lips become tired, when playing staccato, or when the musicians are untrained or older.

With damper use, the escape of air is substantially reduced, except with the F tuba and the French horn when a stopping mute is used.

Anemometry findings confirmed the results of the Schlieren visualizations, showing that flow values are always above about 0.02 m/s. The reasons might include finger or hand movements during playing, air escape from the tone holes, taking a breath between musical phrases, or other convection airflows in the same room. With some instruments, the measured velocity first decreases as the distance from the instrument increases and then begins to increase. This effect may be due to turbulent flow, producing small vortexes that result in varying velocity.

To reduce such flow from all kinds of brass instruments, the researchers said a simple filter could be used, made of cellulose, and taped to the instrument's bell. This will work because the air that is breathed through such instruments escapes entirely through the bell.

With woodwind instruments, air escapes from the tone holes and even leaks from the mouthpiece, in addition to the bell. A filter will not hinder the spread of the air, therefore.

What are the implications?

This data could help discover the range to which exhaled air, potentially containing infectious particles, could spread during infectious airborne disease outbreaks. However, the studies only show the range of larger droplets' spread since small droplets or aerosols are not visualized by Schlieren methods. These results show that airflow does not travel more than 1.2 m into the room.

Secondly, these patterns relate to air blown out by professionally trained singers and musicians. Amateurs and learners may produce very different exhalation patterns and leakage, which may result in a larger volume of air spread into the room.

The movement of the player can also change the velocity of the breathing air, which also varies with the bell diameter and the breathing pressure. Air escaping from the mouth or leaking at the mouthpiece shows a higher velocity of up to 0.15 m/s.

Using this data, the range of spread, dimensions of escaping air, and velocity at which it escapes and spreads, can be estimated for woodwind and brass instruments and professional singers. This would help quantify the risk of viral transmission during such performances so as to develop the best safety precautions for such situations.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:

Becher, L. et al. (2021). The spread of breathing air from wind instruments and singers using schlieren techniques. medRxiv preprint. doi: ... 20240903v1
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Re: Aerosolized Transmission

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Research used to shape how dentistry can be carried out safely during Covid-19

1/11/21 ... id-19.aspx

Leading research at Newcastle University has been used to shape how dentistry can be carried out safely during the Covid-19 pandemic by mitigating the risks of dental aerosols.

It is well known that coronavirus can spread in airborne particles, moving around rooms to infect people, and this has been a major consideration when looking into patient and clinician safety.

Research, published in the Journal of Dentistry, has led the way in helping shape national clinical guidance for the profession to work effectively under extremely challenging circumstances.

The findings have been used by the Dental Schools' Council, Association of Dental Hospitals and the Scottish Dental Clinical Effectiveness Programme to guide key Covid-19 policies for the profession.

Research findings

Research revealed that aerosol generated procedures - such as fillings and root canal treatment - can spray aerosol and saliva particles from dental instruments large distances and contamination varied widely depending on the processes used.

In the open clinic settings, dental suction substantially decreased contamination at sites further away from the patient, such as bays five meters away. Often these distant sites had no contamination present or if contamination was detected it was at very low levels, diluted by 60,000 - 70,000 times.

It was also found that after 10 minutes, very little additional contaminated aerosol settled onto surfaces and therefore is a suitable time to clean a surgery after an aerosol-generating procedure.

" Our research has improved our understanding of dental aerosol generated procedures and identified how cross-contamination could be a risk for spreading Covid-19.

When the pandemic began, dental services were significantly reduced and there was an urgent need by the profession to focus on how dental clinics could work in a safe environment for patients and staff.

We now have a much greater understanding of where the splatter of aerosols go and how far they travel during different procedures and settings, allowing clinical teams to make informed decisions to protect people.

I am pleased that our research here at Newcastle has been used nationally by leading dental bodies to inform their policies on how the profession should carry out procedures during the pandemic."

- Dr Richard Holliday, NIHR Clinical Lecturer in Restorative Dentistry at Newcastle University, UK

Collaborative effort

A research team from the School of Dental Sciences, including clinicians, dental nurses, microbiologists and scientists carried out the study.

The team used the tracer dye, fluorescein, while carrying out aerosol-generating procedures on a dental mannequin to analyse how far and where aerosol particles and saliva travelled from the patient's mouth.

A range of procedures were done and the effect of suction and ventilation analysed. Experts looked at contamination close by and also in an open plan clinic.

Kimberley Pickering, a research dental nurse involved in the study, said: "For the safe re-opening of dental services, it was essential to understand the behaviour of the aerosols that come out of a patient's mouth during dental work.

"We now better understand where the aerosols go and how far they travel during different procedures and settings.

"We also understand how dental aerosols settle over time, which has helped inform cross-infection control procedures."

Further research will continue to focus on where aerosol and droplets from dental instruments travel and how far they go. Experts will also look at how long aerosols hang around in the air and examine a number of common dental procedures and methods of controlling aerosols.

A key part of the research will investigate if viruses can be carried in dental aerosols, and if viruses remain infective at a distance from the procedure. This will help experts to understand how to reduce the risk of microbes, like Covid-19, being spread by aerosols during dental treatment.

Student case study

The research led the team to develop a new clinic configuration to allow the safe return of dental students and their patients.

Newcastle University's School of Dental Sciences is one the first universities in the country to recommence teaching aerosol-generating procedures to students in person during the pandemic.

Fourth year student Paddy Crawshaw said: "Being a dental student during the pandemic has been a big challenge, but dental students feel lucky to come into University every day and get in-person teaching as it's a privilege to treat our patients.

"The Dental School has been very supportive since the pandemic began. It is clear that senior clinicians and academics have worked hard behind the scenes to allow us to return to clinical teaching.

"The common goal of delivering first-class treatment for our patients has enhanced the Dental School's sense of community and this has really helped me through this term.

"I am proud of the way Newcastle Dental School and all of its staff and students have come together in the face of adversity through the Covid-19 pandemic. To know we are one of the first schools in the country offering a full range of student-led treatments for our patients makes me feel lucky to be studying here.

"Due to the extensive research undertaken by the School I have never felt unsafe, whether extracting a tooth or doing a simple examination I know the School's protocols are allowing me to work safely."


Newcastle University

Journal reference:

Holliday, R., et al. (2021) Evaluating contaminated dental aerosol and splatter in an open plan clinic environment: Implications for the COVID-19 pandemic. Journal of Dentistry.
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