The aerosol discussion is a thing of the past in the scientific world, as evidenced by the medical follow-up studies on the generation of aerosols. I came across a study that shows that singing and speaking generate many more aerosols than coughing and sneezing. When coughing/sneezing, the large droplets, which were traditionally seen as the main contaminants, end up on the ground within one and a half meters. The small, almost weightless droplets, which are mainly released when speaking and singing, float longer, ready to be inhaled.
Curious about how aerosols are actually created, I ended up with nebulizers. These are used, for example, in inhalation equipment. One particular type, the ultrasonic nebulizer, has remarkable similarities with voice use. The similarity is so thick on top that I wonder why everyone is so obsessed with falling droplets within one and a half meters, sneezing, 'coughing' – and that while just speaking - and certainly singing - might produce more aerosols? That can't be true, can it? Maybe so. First a simple explanation of atomization or aerosol production, then the reference to the science behind it.
Aerosol production
Vernevelaars en inhalatoren moeten (tenzij ze poeder verstuiven, dat kan ook) vloeistof omzetten in druppeltjes die klein genoeg zijn om te inhaleren. Er zijn verschillende systemen en apparaten, afhankelijk van de toepassing. De basis is hetzelfde. Het begint vaak met geluidstrillingen. ultrasoon, zodat we geen last hebben van gebrom of gepiep. Dus:
- aerosols are vibrated with sound vibrations (singing/resonance are also sound vibrations)
- pressure is built up to spray them outwards (pressure on diaphragm, squeezing vocal cords)
- The aerosols are forced out through a (too) small opening or narrow slit to 'atomize' them (voice slit)
Because of the desired volume, the breathing pressure is increased higher and breathing is deeper and 'from the abdomen'. I assume less shallow breathing, more from the lower airways. That is precisely where the biggest infection problems arise.
Remember that in (group) conversations you are generally speaking one by one. When singing and cheering, dozens (hundreds) of people can 'speak' at the same time, at volume and breathing deeply. That means a much larger aerosol production. Do this in poorly ventilated rooms and it is not surprising that you hear a relatively large amount about infections through choirs and churches.
(EDIT for Maarten Keulemans: Natural ventilation is bad ventilation if there is not enough wind. What counts is the 'ventilation rate'. That must be much higher for a choir than for an office space. I hope I don't have to do the math.)
Nice hypothesis, so I googled it and yes: virologists have known it for a long time! (Not in the Netherlands of course, but elsewhere it is). This article from February 2019 confirms this and contains several links to previous research on aerosols and the importance of aerogenic spread in infectious respiratory diseases.
Below are some facts from the article https://www.nature.com/articles/s41598-019-38808-z , where they Comparing coughing, sneezing, speaking and singing in terms of aerosol emissions. It goes without saying that aerosol clouds can cause infections, as has been shown in countless other studies. As long as this is not accepted by WHO and RIVM, it will continue to fight a losing battle in the Netherlands, mopping up with the tap open.
It could also explain why the Japanese colleague of Prof. Dr. Voss was unable to obtain a good aerosol sample, right in front of the mouth of a corona patient. If only that patient had sung a piece...
[EDIT 31-10: By the way, it is now others managed to sample 'viable' SARS-Cov-2. (opens in new tab) ]
Fun facts
- The louder the voice volume, the more aerosols (think of environments with loud music such as après-ski, carnival)
- zingen genereert 6 keer zoveel aerosolen als normaal praten
- 10 seconden zingen levert net zoveel aerosolen op als een hoestbui van 10 seconden
- 30 seconden hoesten staat gelijk aan 30 seconden “aah” zeggen
- sommige mensen genereren opvallend veel meer aerosolen dan anderen tijdens het praten. De oorzaak daarvan is nog niet duidelijk. Zulke mensen zullen dan ook een relatief groot aandeel hebben bij superspread events.
- een goed mondkapje minimaliseert de uitstoot van grote en kleinere druppels en vermindert de aerosolenuitstoot. [edit: Ca. Vermindert met max. 10% bij de meest gangbare mondkapjes]
Aerosolen vormen sowieso al een belangrijker besmettingsgevaar dan grotere nies- en hoestdruppels, want
- ze blijven langer in de lucht hangen dus hebben een grotere kans ingeademd te worden
- de kleinste druppeltjes komen makkelijker diep in de longen terecht waar ze zwaardere infecties veroorzaken.
Overigens komen alle bovenstaande beweringen uit het rapport van het onderzoek in Nature, ik verzin het echt niet zelf.
‘Zachte g’ versus ‘Harde g’
In dit kader is dit recente artikel ook aardig. De Engelse klank “th” genereert de meeste druppeltjes van alle klanken (je ziet in de video alleen de druppeltjes die deze camera kon registreren, ik neem aan dat microscopisch kleine druppeltjes niet gefilmd zijn). Ik ben benieuwd wanneer het RIVM erachter komt dat een ‘zachte g’ fijnere en dus gevaarlijkere aerosolen genereert dan de ‘harde g’… maar dat heb ik dan wel gewoon zelf gefantaseerd 🙂 .
Enfin, Gisteravond was er weer een corona-persconferentie met Rutte en de Jonge. Het woord ‘ventilation‘ kwam er niet eens in voor. Het is om radeloos van te worden.
