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This is he pee e iewed e sion o he ollowing a icle: [Ma ín-
Ga cía D, Moyano-Campos JJ, Bien enido-Hue as JD. Dis ances o
ansmission isk o COVID-19 inside dwellings and e alua ion o he
e ec i eness o ecip ocal p oximi y wa ning sounds. Indoo Ai . 2021; 31: 335
347. h ps://doi.o g/10.1111/ina.12738], which has been published in inal o m
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Dis ances o ansmission isk o Co id-19 inside dwellings and e alua ion
o he e ec i eness o ecip ocal p oximi y wa ning sounds
Da id Ma ín-Ga cía1*, Juan Moyano-Campos 1, Da id Bien enido-Hue as2
1Depa men o G aphical Exp ession and Building Enginee ing, Highe Technical School o
Building Enginee ing, Uni e si y de Se ille. 4A Reina Me cedes A enue, Se ille 41012, Spain
2Depa men o Building Cons uc ion II, Highe Technical School o Building Enginee ing,
Uni e si y de Se ille. 4A Reina Me cedes A enue, Se ille 41012, Spain
*Co esponding email: [email p o ec ed]
ABSTRACT
One o he main modes o ansmission and p opaga ion o Co id-19 (SARS-CoV-2) is he di ec
con ac wi h espi a o y d ople s ansmi ed among indi iduals a a ce ain dis ance. The e a e
indoo spaces, such as dwellings, in which he ansmission isk is high. This esea ch aims o
eco d and analyse isk close con ac s in his scope, expe imen ally assessing he e ec i eness
o using elec onic p oximi y wa ning sound de ices o sys ems. Fo his pu pose, he
me hodology is based on moni o ing he loca ion o he occupan s o a dwelling. Then, he days
in which a p oximi y wa ning sound sys em is ins alled and ac i a ed a e compa ed o he days
in which he sys em is no ac i a ed. The esul s s essed he signi ican educ ion o ime and
numbe o close con ac s among indi iduals when he wa ning was ac i a ed. Rega ding he
ela ion be ween he numbe and he du a ion o close con ac s, oge he wi h he educ ions
men ioned, he possibili y o making ce ain p edic ions based on he dis ibu ions ob ained is
p o ed. All his con ibu es o he p og ess in he p e en ion o Co id- 19 ansmission because
o close con ac s in dwellings.
KEYWORDS:
Co id-19; dwellings; close con ac s; p oximi y wa ning.
PRACTICAL IMPLICATIONS
-Cu en ly, Co id-19 is a global epidemic ha causes hund eds o housands o dea hs and high
economic epe cussions a ound he wo ld. Despi e ad ances in diagnosis and ea men , he
global incidence emains high and addi ional s a egies o p e en ion a e u gen ly equi ed.
-This s udy p o ides he i s empi ical da a showing ha he applica ion o an elec onic
p oximi y wa ning sound sys em is e ec i e in imp o ing he con ol o a Co id-19 ou b eak
in indoo en i onmen o a dwelling, also being a b eak h ough in eco ding sys ems and
analysing he isk o close con ac s in dwellings and in he possibili y o p edic o he numbe
o such con ac s.
1. INTRODUCTION
Ce ain beha iou s and cha ac e is ics o indi iduals a e di ec ly ela ed o he le el o in ec ion
isk 1 3, and close con ac s a e he main causes o he expansion o many i al espi a o y
diseases 4 9. These close con ac s usually en ails a ce ain in e pe sonal dis ance which
acili a es he inhala ion o i al d ople s 10,11. B ea hing, alking, coughing, and sneezing a e
ac i i ies ha p oduce such d ople s in a ious amoun and size 12 16. The dis ance ha hese
d ople s can each, and he e o e he secu i y dis ance among indi iduals, has been epea edly
s udied o se e al ypes o si ua ions 17 19.
Since 31 Decembe 2019, when he Wuhan Municipal Heal h Commission (Wuhan is in he
p o ince o Hubei, China) communica ed o he Wo ld Heal h O ganisa ion (WHO) he
exis ence o pa ien s a ec ed by Co id-19, he wo ld scien i ic communi y knows much be e
his i us, pa icula ly i s in ec ious beha iou . Simila ly o o he co ona i us, he main mode
o ansmission, al hough no he only one 20 22, is he con ac wi h espi a o y d ople s, ha is,
he mucus o he mou h, nose o eyes 23, as he i us is ound in nasopha yngeal sec e ions and
sali a 24. Thus, he modes o ansmission and p opaga ion among indi iduals, i indi iduals do
no use o he means o p o ec ions, a e di ec ly ela ed o he dis ance among hem and he
exposu e ime. A close in e pe sonal dis ance implies a g ea e inhala ion o he i us, hus
inc easing he isk o in ec ion h ough he close con ac ou e 25. A e analysing he exis ing
esea ch s udies ying o es ablish he mos adequa e secu i y dis ance, i is clea ly deduced
ha he e is no unanimi y when es ablishing an accu a e unique dis ance 26 because many
ac o s could a y he dis ance om a me e o eigh o nine me es o speci ic si ua ions, such
as sneezes 27,28. Howe e , a ious bodies and coun ies ha e ecommended o keep minimum
dis ances among indi iduals be ween one 29 and wo me es 30 because his is gene ally a
easonable measu e o educe he isk o in ec ion as long as he e a e no o he ac o s
con ibu ing o p opaga ion, such as s ong sneezes, ai cu en s, in ec ious ae osols in closed
spaces 31 o con ac s wi h con amina ed su aces 32.
Recen esea ch s udies 33 and expe s like B omage 34 indica ed ha mos ansmissions a e he
esul o he sp ead o he in ec ion a home. I a amily membe is in ec ed ou side he dwelling,
hen he o he membe s usually become in ec ed when he in ec ed indi idual e u ns. This ac
is con i med by Qian e al. 33, who iden i ied 318 ou b eaks wi h 3 o mo e cases, in ol ing
1,245 cases con i med in 120 ci ies.
The scien i ic li e a u e ela ed o ansmissions in buildings 35, he sp ead o in ec ion in amily
en i onmen s and households 36 and he beha iou o close con ac s including he body
posi ioning in de ail 37 is almos unanimous in conside ing ha in a closed a chi ec u al
en i onmen , such as dwellings and simila spaces, he isk o ansmission due o p oximi y is
high, pa icula ly i an occupan is in ec ed ou side and li es wi h he o he occupan s o he
dwelling. The main easons a e he cha ac e is ics o hese closed spaces and he
beha iou because he e is usually a g ea e in e ac ion among hem 38, pa icula ly in modes
dwellings and in si ua ions in which he cohabi a ion is in ensi ied 36. In hese cases, he
ansmission isk is closely ela ed o he dis ance and posi ion among indi iduals, he numbe s
o indi iduals, he ac ions ela ed o he expulsion o con amina ed d ople s (sneezing,
coughing, speaking o jus b ea hing), and he exposu e ime, among o he speci ic
cha ac e is ics o hese spaces. Ne e heless, he le el o p esence o he i us due o he
exposu e ime is he acking basis o he isk close con ac . Al hough sneezing o coughing
implies su icien i al d ople s o di ec ly in ec , some minu es alking ace- o- ace o an
in ec ed people 10,39 and e en 20 minu es exposed o hei b ea hing a e necessa y o be in ec ed,
all his based on he numbe o d ople s expelled and ecei ed pe minu e 34.
Va ious companies and en ep eneu s om he echnological sec o a e oday o e ing wa ning
sound de ices and sys ems which, wi h g ea e o lowe success, in end o de ec he ecip ocal
p oximi y among indi iduals. These de ices o sys ems a e applying se e al echnologies and
p ocedu es and a e p esen ed in a ious o ma s, such as independen uni s, applica ions o
sma phones, e c. This esea ch is he e o e ocused on analysing he e ec i eness o hese
de ices by applying hem in a dwelling whose dimensions, cha ac e is ics, and amily uni a e
ela i ely common. Fo his pu pose, his esea ch is based on he s udies on he human
beha iou when he e a e non- e bal wa ning sounds 40,41. In addi ion, an expe imen al
campaign is conduc ed in a eal en i onmen by using spa ial posi ion loca o s, and a sys em
ha gene a es a wa ning sound i ecip ocal p oximi y is de ec ed among indi iduals is
es ablished. I should be emphasized ha i he e is no in ec ed indi idual in he dwelling, hen
amily membe s can be close. Fo his eason, his esea ch ocuses bo h on he hypo hesis ha
he isk exis s when a amily membe mee s o he indi iduals, becomes in ec ed and e u ns
home and on he analysis o o wha ex en hese de ices o sys ems a e e ec i e o con ol and
p e en in ec ions ela ed o social dis ance, such as he case o Co id-19.
2. SIMILAR WORKS

Se e al esea ch s udies ha e eco ded he eal- ime loca ion o indi iduals and ha e analysed
he du a ion and dis ance o con ac s in a ce ain pe iod and in a ious indoo spaces 2,37,42 46;
howe e , no esea ch analyses and compa es he esul s om ac i a ing o no a wa ning sound
de ice o sys em o a oid close con ac and he e o e ansmission in a dwelling like ha
chosen.
3. MATERIALS AND METHODS
As a es bed, a dwelling loca ed in he sou h o Spain was used. I s cha ac e is ics and he
amily uni li ing in i a e usual in his coun y 47.
3.1. Cha ac e is ics o he dwelling and amily uni
The dwelling has a hall, a li ing-dining oom, a ki chen, h ee bed ooms, wo ba h ooms, a
balcony, and a co ido , all made independen by walls and doo s. The occupan s o he amily
uni a e ou indi iduals (a man, a woman, a boy, and a gi l). The adul s a e be ween 40 and 50
yea s old, and he subjec s unde 18 a e 10 and 12 yea s old. All occupan s ha e been li ing in
he dwelling o mo e han en yea s, so hey a e amilia ized wi h he expe imen al
en i onmen , hus compensa ing any bias o igina ed by ha en i onmen . The ac ual spa ial
cha ac e is ics, dimensions, uses, su aces, and u ni u e o he dwelling a e eliably ep esen ed
wi h he lowes possible e o by using a h ee-dimensional modelling Au odesk Re i 2019®
48. The model and ep esen a ion o he loo s co esponding o he dwelling (Fig. 1) a e used
in he g aph o he loca ion da a ob ained.
3.2. De ec ion de ices
Fo he expe imen al phase, de ec ion de ices we e used o he eal- ime loca ion o each
subjec . Gi en ha hese de ices should p o ide eadings as accu a e as possible ega ding he
eco ding o he loca ion om which he in e pe sonal dis ance could be deduced, he
echnologies no mee ing hese equi emen s we e no conside ed, ollowing he speci ici ies o
he scien i ic li e a u e 42,49,50. As a esul , he eal- ime loca ing sys em (RTLS) based on ul a-
wide band (UWB) was he mos adequa e echnology o he pu pose o his esea ch 49,51
55. Based on bo h he compa isons conduc ed by o he au ho s 56 and ou analysis and a ailable
esou ces, a Decawa e® 57 equipmen was chosen as he e we e expe imen al p eceden s in
se e al spaces and si ua ions 58 65. This equipmen is an ul a-wideband ne wo k cons i u ed by
ixed nodes (ancho s) and mo ing nodes ( ags). Rega ding he accu acy, al hough
±10 cen ime es and second in e als, o he
indica ions we e also conside ed 66,67. Howe e , hese echnical cha ac e is ics we e adap ed o
he basic equi emen s o his ype o expe imen a ion in ela ion o he eal- ime collec ion o
mode which each expe imen al subjec pe manen ly had, and he emaining ancho s we e
placed in he walls o he dwelling nea o he ceiling. The sys em gene a ed eal- ime da a
which we e collec ed by a mobile de ice and a compu e hough he p ocedu e, he so wa e
and he APIs indica ed by he manu ac u e . On he o he hand, an Excel® sp eadshee was
used o he da a compila ion and p ocessing, and Mic oso Visual S udio®68 o he
p og amming o some algo i hms, as well as H ml, Php, and Mysql, among o he s. When an
indi idual was ge ing close o ano he o o he s om a ce ain dis ance, a no e y high sound
signal, bu audible, was gene a ed, whose one and in ensi y we e p e iously chosen by he
expe imen al subjec s o be as mos pleasan as possible. To sum up, he sys em was designed
by placing ancho s in se e al poin s o he dwelling and ags o he expe imen al subjec s (Fig.
2), so he loca ion da a o hese subjec s we e gene a ed. A e da a p ocessing, he dis ances
among subjec s we e de e mined, and all was coo dina ed by po able Blue oo h Speake s o
he p oximi y wa ning sound sys em among indi iduals. The placing o he ancho s he e o e
cons i u ed a coo dina e sys em o an o igin co esponding o one o hese ancho s, so he
dis ance om each ag o each ancho was calcula ed, hus allowing he ags o be always placed
as he ini ial coo dina es o he ancho s we e known because hey we e p e iously de e mined.
Las ly, be o e s a ing he expe imen a ion, he co ec calib a ion o de ices was checked by
e i ying i he o e ed da a co esponded o ac ual da a.
3.3. Dis ance and isk posi ion conside ed
This s udy only conside ed he dis ances among expe imen al subjec s and no hei co po al
posi ion due o he easons men ioned below.
To make he goal o he esea ch easible ega ding he compa a i e s udy, he concep o isk
con ac o was ini ially es ablished in a unique, clea and accu a e way.
Conside ing he au ho s a o emen ioned and he indica ions gi en by he mos known
in e na ional heal h o ganisa ions, such as WHO 29 o he Eu opean Cen e o Disease
P e en ion and Con ol (ECDC) 30, he app oaches a a dis ance less han 2 me es o
a household as long as he con ac ook place wi hou
p o ec ion ( ace mask, eye p o ec ion, e c.). Rega ding ime, al hough he du a ion o 15 minu es
is used in ce ain scopes 30, he secu i y ma gin was inc eased by using 10 minu es. The same
occu ed when 2 me es we e chosen, ins ead o 1 me e, as ecommended in some cases.
As o he exposu e ime, he e is no absolu e ce ain y o how many pa icles should be inhaled
and he e o e how much exposu e ime is necessa y in each ci cums ance o p oduce a
ansmission. Fo his eason, his s udy uses a ime ma k ha may seem high bu assu es ha
he esul s e lec high- isk con ac s.
A e coun ing close con ac s, al hough hey we e i s de ined as episodes o 10 con inuous
minu es a less han 2 me es in some momen s, some cases we e no s ic ly sui able o hese
condi ions. Howe e , hese cases we e also conside ed because one o hese condi ions was
ul illed and he o he was almos ul illed.
The goal o he esea ch was no o es ablish whe he ansmissions would ake place a o he
dis ances o exposu e imes di e en o hose p e iously chosen. The main goal was o assess
he e ec i eness o p oximi y wa ning sound de ices o sys ems wi h espec o
beha iou when a oiding dis ances which could imply his ansmission, ega dless o whe he
he ansmission was p oduced, so he easonable and ounded e e ences chosen we e enough.
3.4. Da a collec ion and p ocessing
Rega ding he da a collec ion, all occupan s we e moni o ed om he hou in which he i s
occupan go up in he mo ning o he hou in which he las occupan wen o bed a nigh , so
he p og ammed ime was om 8:00 a.m. o 24:00 p.m. (16 hou s). When a subjec go up, he
loca ion de ice was immedia ely placed and ac i a ed. Howe e , he connec ion o he wa ning
sound de ice was no ac i a ed un il a leas 2 subjec s go up, a ound 9:00 a.m. On he o he
hand, he subjec s on bed a e 8:00 a.m. we e assigned a ixed coo dina e o hei loca ions
which coincided wi h he lying posi ion in hei espec i e bed un il hey also go up and he
loca ion de ise was placed and ac i a ed. The expe imen al days coincided wi h he
con inemen days dec eed by he Spanish Go e nmen in Ma ch 2020, so all amily membe s
s ayed in he dwelling all he expe imen al hou s. The in e nal empe a u e was be ween 21 and
23 ºC. Acco ding o he Spanish Building Technical Code, he en ila ion a e o dwellings was
0.94 ai changes pe hou . In hese expe imen al days, he dis ances o he ags o each subjec
o he ancho s we e ob ained a each momen . Wi h hese da a and by iangula ion, he
coo dina es (x, y) o each indi idual we e au oma ically ob ained in eal ime, and he
coo dina e (z) was no equi ed, as p e iously jus i ied, conside ing he goal. No all he
coo dina es we e he esul o he da a eco d p o ided by he loca ion de ices because hese
we e upda ed based on he ac i i y o he mo emen senso . In addi ion, ce ain dispa i ies we e
u n en ails he dis ibu ions and hei espec i e g aphs. This esea ch showed ha sho close
con ac s we e he mos usual, hus dec easing he equency as he du a ion inc eased by
ollowing a loga i hmic dis ibu ion.
The ansmission isk inc eased by educing he in e pe sonal dis ance, and ice e sa 18,69
71. Al hough he loca ion o indi iduals could no be accu a ely quan i ied a each momen ,
human beha iou usually a ied acco ding o ce ain ac o s al eady men ioned 2,3. Based on
he esul s, all subjec s esponded o he wa ning in a simila way mos o he ime. Gi en he
amily uni and he dwelling analysed, i would be in e es ing and e en in ce ain cases
necessa y o expe imen wi h se e al dwelling ypologies and amily uni s o di e si y he es
bed and o ob ain mo e da a o e i y he esul s, and e en o add conclusions.
Rega ding he esul s o he means o he dis ances in he day when he wa ning sound was no
ac i a ed, he mean pe sonal dis ances in case o mo e a ec i e subjec s we e he mos equen
and some imes e en ine i able, al hough he wa ning sound was connec ed. These isk con ac s
we e usual acco ding o wha some au ho s indica ed 25,37.
As o he ac i i ies and he way o ci cula ion o subjec s h oughou he day, al hough habi s
s ongly in luenced he p obabili y o close con ac s, he esul s also showed ha hese habi s
could be modi ied by he wa ning sound, hus g ea ly educing hese con ac s, a leas in he
sho e m. In his ega d, he subjec s, who a he same ime we e ca ying ou di e en
ac i i ies, usually eco ded a low p obabili y o con ac among hem, hus indica ing ha he
design o dwellings should in luence his aspec con ibu ing ha each subjec has hei own
space acco ding o he ac i i y. In his manne , subjec s could ca y ou hei ac i i ies in a
zones, pa icula ly i hey we e awa e o a possible close con ac , such as he case when he
wa ning sound was ac i a ed.

On he o he hand, he zones wi h com o able sea s we e usually ho spo s o con ibu e o close
con ac s, and i hese sea s we e big, such as he so a, and play ul ac i i ies could be ca ied
ou , hey u ned in o a space whe e con ac s we e equen e en wi h he wa ning sound
connec ed, as subjec s usually sa oge he .
Ano he aspec was a high p obabili y o sho close con ac s when he subjec s wen om a
poin o ano he o he house as he subjec s who coincided in he passing places o he dwelling
did no gene ally ha e enough space as hese zones we e no wide enough o keep he dis ance
equi ed. Ne e heless, con ac s we e sho and spo adic in hese cases. The pe o mance o he
senso s was gene ally adequa e; howe e , o ely on he mo ion senso s, hese we e checked a
in e als simila o he imes es ablished o conside close con ac s. Da a we e no gene ally
co ec ed, bu when he ags we e away om he ancho s o when he e we e mo e obs acles
be ween hem da a we e co ec ed.
Finally, hese esul s could be use ul o analyse he isk o in ec ion a a g ea e scale. Fo
ins ance, i he numbe o dwellings, hei ypology, and amily uni s in he households o a
ce ain zone a e known, he numbe o close con ac s which could be educed by applying
wa ning sound de ices o sys ems could be calcula ed.
6. CONCLUSIONS
The p obabili y o isky close con ac a a dis ance less han 2 me es is e y high in closed
spaces, such as dwellings, and he human beha iou inside hem is a de e minan ac o o he
ansmission isk.
Close con ac s could be dec eased wi h hese wa ning sound de ices o sys ems, making he
con ac s almos null.
Bo h when he wa ning de ice was disconnec ed and connec ed, he li ing- oom o he
dwelling, and pa icula ly he so a, he zones in which people usually ea , and he ki chen we e
he zones whe e close con ac s we e mo e equen and he e o e he e was a g ea e p obabili y
o p oximi ies a a dis ance less han 2 me es o mo e ime. In his ega d, he subjec s ca ying
ou di e en ac i i ies a he same ime usually eco ded a low p obabili y o con ac among
hem, hus indica ing ha he design o dwellings should acili a e ha each subjec has hei
own space o he espec i e ac i i ies. Howe e , he e was an impo an dec ease o close
con ac s in hese places when he wa ning sound was connec ed.
On he o he hand, i he wa ning was disconnec ed, he esul s indica ed ha he ela ion
be ween du a ion da a and he sum o con ac s ollowed loga i hmic dis ibu ions. I he wa ning
was connec ed, he dis ibu ion was linea a e a ound 5 minu es, o exponen ial including
hese 5 minu es, so p edic ions could be made wi h a de e mina ion coe icien g ea e han
80%. Based on he da a o some o hese wo a iables, he o he a iable could be deduced
wi h a p obabili y o success o 80%, al hough his limi should be inc eased by s udying a mo e
ex ensi e casuis y.
Rega ding a mo e long- e m easibili y o using wa ning sounds in a dwelling, and acco ding
o wha expe imen al subjec s mani es ed, i could be less easible i i is in ended o be used
o a long ime. On he o he hand, he e a e s ill si ua ions in which secu i y dis ances a e no
espec ed consciously, whe he he wa ning is connec ed o no , ei he because i is ma e ially
di icul o ul il acco ding o he cha ac e is ics o he dwelling o because he op ions o
al e na i es o he dis ance a e con a y o ce ain habi s which subjec s do no wan o
enounce ega ding hei ela ionships as amily uni . Finally, as he day passed, he wa ning
was less e ec i e.
Funds and con lic s o In e es : This esea ch has no been inanced. The au ho s decla e no
con lic s o in e es s.
Da a a ailabili y s a emen : Resea ch da a a e no sha ed.
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