dimension of sars-cov-2 vs airborne particles

Manuel Gameiro da Silva

Vice-President of REHVA

University of Coimbra

[email protected]

Indoor Air Quality (IAQ) Concepts Case Study COVID-19

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SARS-CoV-2

PM 1

PM 5

PM 10

(NIAID-RML)HEALTHThis Is What The COVID-19 Virus Looks Like Under The MicroscopeJACINTA BOWLER14 FEBRUARY 2020

80-140 nm ≈ 0.1 m

m X 1000 = 1 mm

Virus is about 300 times bigger than the molecules of Nitrogen and Oxigen (≈ 0.000300

m)

Ø < 1 m

Virus is 600 times thinner than a hair

Dimension of Sars-CoV-2 vs Airborne Particles

3Particle Size Ranges in the indoor air

Particle Size Range( m)0.001 0.01 0.1 1 10 100

Airborne Particles

Diesel Particles

Tobacco Smoke

Plant SporesGas Molecules

Viruses Bacteria Pollen

4Airborne Particles

Diameter ( m) Nível de Penetração Classificação

> 7 Oral and Nasal CavitiesInhalable

4.7 – 7 Larynx

3.3 – 4.7 Trachea and BronchiThoracics

2.1 – 3.3 Secondary Bronchioles

1.1 – 2.1 BronchiolesBreathable

0.65 – 1.1 Alveoli

Smaller particles have a higher hazard index, can cause alveolar obstruction and impede respiratory function.

7Emission of Exhaled Droplets

0.1 1 10 100 1000

10

100

1 000

10 000

100 000

1 000 000

Dimensão das Partículas ( m)

Núm

ero

de P

artíc

ulas

Stephanie Taylor, “Optimize Occupant Health, Building Energy Performance and Revenue through Indoor-Air Hydration,” 19 November 2019, Atlanta: ASHRAE.

Sneezing

Coughing

Talking

Farhad Memarzadeh, “Figure 1 Particle generation by sneezing, coughing and during talking,” [https://www.researchgate.net/publication/234076687_Improved_Strategy_to_Control_AerosolTransmitted_Infections_in_a_Hospital_Suite]

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Role of ventilation in the control of the COVID-19 infection: Emergency presidential discourse SHASE, March 23, 2020.

Transmission/Contamination Modes

Mode PM Size MeasuresAirborne < 10 Mask, Face Shield, Ventilation

Droplets 10<D<50 Confinement, Social Distancing

Contact > 50 Hygiene, Disinfection, Behavior

Jianjian Wei; Yuguo LiBuilding and EnvironmentVolume 93, Part 2, November 2015, Pages 86-96https://doi.org/10.1016/j.buildenv.2015.06.018

Fig. 5. Instantaneous dispersion pattern of particles (t = 100 s) in the buoyancy-neutral jet (mouth opening diameter D = 2 cm, initial velocity u0 = 10 m/s, Tamb = 25°C). Particles are continuously released from t = 0. The top-hat width of the jet is indicated by the dashed line, which collapses with the visible boundary of the jet.

Enhanced spread of expiratory droplets by turbulence in a cough jet

Contact

Conclusion

• The safety distance of 2 m between people, regarding the risk of COVID-19 infection, is a myth

• The Mode of Transmission through Airborne Particles (Aerosols) is possible, because the virus remains viable and infectious for at least 3 hours.

• These particles, remain in suspension, follow the internal flows and their deposition rate is residual.

Does it exist a safety distance?

Drops

Airborne2 m

Masks Effects

Effect of Protective Measures

Three countries with 10 millions inhabitants

Country Transmission ModesProtection Protective Measures

Czech Rep Airborne, Droplets, Contact Masks, Ventilation, Confinement, Distancing , Hygiene, Disinfection, Behavior

Portugal Droplets, Contact Confinement, Distancing , Hygiene, Disinfection, Behavior

Sweden Contact Hygiene, Disinfection, Behavior

Population Age Median Life Espectancy Population Density Urban Pop (%)Cz 10 708 982 43.2 79.8 138 (p/km2) 73.5Pt 10 196 707 46.2 82.7 112 (p/km2) 65.9Sw 10 092 270 41.1 83.3 25 (p/km2) 87.9

Effect of Protective Measures

Breakdown of the Probabilitiesof Transmission Modes

Airborne: 64%

Droplets: 21%

Contact: 15%0

100

200

300

400

500

600

Interned in ICUs vs Protection for Transmission Modes

Sweden

Portugal

Czech Rep

Contact; Droplets

Contact

?

Contact; Droplets; Airborne

Cases /Tests

0.038

0.088

0.198

• Face-to-face meetings, during the epidemic crisis, should not be held.

• Indoor spaces with human occupancy must be heavily ventilated, exclusively with fresh air, to decrease virus concentrations, in the event of possible contamination by suspended particles, and to reduce the risk of infection.

• When planning an exit, to crowded spaces, you should wear a mask and, if possible, a visor. Normal masks are not completely effective in preventing the smallest particles. The visor substantially increases the prevention effectiveness.

• Those who work in public places should wear a mask and visor to protect the airways.

Conclusion

April 28, 2020, Jarek KurnitskiREHVA COVID-19 Task Force

How to operate and use building services in order to prevent the spread of the coronavirus disease (COVID-19) virus

(SARS-CoV-2) in workplaces

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Transmission routes

(a) viral particles accumulate in the lungs and upper respiratory tract

(b) droplets and aerosolized viral particles are expelled from the body through daily activities such as coughing, sneezing, talking, and non-routine events such as vomiting, and can spread to nearby surroundings and individuals

(c) Viral particles, excreted from the mouth and nose, are often found on the hands and

(d) can be spread to commonly touched items

Leslie Dietz et al, 2020 Novel Coronavirus (COVID-19) Outbreak: A Review of the Current Literature and Built Environment (BE) Considerations to Reduce Transmission

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Transmission routes

1. Close contact, large droplets > 10 m (<1 m distance), but rule of thumb 2 m

2. Airborne transmission, small particles, droplet nuclei < 5 m stay airborne for hours

3. Via surface (fomite) contact

4. Faecal-oral route

Dark blue: evidence exist

Light blue: evidence for SARS-CoV-1

Infected PersonDroplets

Droplet Nuclei

Droplet Nuclei

Droplets

Droplets

Airborne

Faecal−Oral

Direct Contact

Indirect Contact

5Settling distance of droplets

• Small water droplets evaporate in milliseconds, even 10 m in 0.2 s

• In the mixture of volatiles (mainly water) and nonvolatile substances the final diameter would be about half the initial diameter

• 1 μm to 100 μm range under interest, the rapid factor of 2 change in diameter often considered

• To estimate the settling distance of 1 m, low indoor air velocity 5 cm/s used (higher velocity will increase the distance)

Morawska 2006

0

0.2

0.4

0.6

0.8

1

1.2

0 2 4 6 8 10 12 14 16

Heig

ht, m

Distance traveled, m

Indoor air velocity 5 cm/s

50 micron

30 micron20 micron

10 micron5 micron

7Example of a crowded space with poor ventilation

• Yuguo Li et al. 2020 preprint: https://doi.org/10.1101/2020.04.16.20067728

– Chinese restaurant, where ventilation about1 L/s per person

– An index patient infected 9 persons

– Results show that the infection distribution is consistent with a spread pattern of exhaled virus-laden aerosols driven by AC circulation airflow

• Hospital evidence: no infection risk at 2 m distance https://doi.org/10.1016/j.scitotenv.2020.138401

– CO2 measurement allow to estimate ventilation at at least 36 L/s per person

DOE Better Buildings Webinar Series

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Ventilation and building services guidance

• Traditional infection control pyramid adapted from the US CDC (CDC 2015)

• Until vaccine and medicaments are not available, ventilation is No 1 infection control measure

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Longer and continuous ventilation operation

• Extended operation times are recommended: Change the clock times of system timers to start ventilation at nominal speed at least 2 hours before the building usage time and switch to lower speed 2 hours after the building usage time

• Do not switch off ventilation at nights and weekends, but operate at lowered speed

• Extended ventilation will remove virus particles from air and also released virus particles from surfaces out the building

• The general advice is to supply as much outside air as reasonably possible. The key aspect is the amount of fresh air supplied per person

• Enlarge the spacing among employees (min physical distance 2-3 m between persons) in order to foster the ventilation cleaning effect

• Exhaust ventilation systems of toilets should always be kept on 24/7, and make sure that under-pressure is created, especially to avoid the faecal-oral transmission

10Humidification and air-conditioning have no practical effect

• SARS-CoV-2 stability (viability) has been tested at typical indoor temperature of 21-23 and RH of 65% with very high virus stability at this RH. Together with previous evidence on MERS-CoV it is well documented that humidification up to 65% may have very limited or no effect on stability of SARS-CoV-2 virus.

• Therefore, the evidence does not support that moderate humidity (RH 40-60%) will be beneficial in reducing viability of SARS-CoV-2, thus the humidification is NOT a method to reduce the viability of SARS-CoV-2.

• SARS-CoV-2 has been found highly stable for 14 daysat 4 ; 37 for one day and 56 for 30 minuteswere needed to inactivate the virus (Chin et al, 2020)

• AC has no effect in this context (recirculationexcluded)

van Doremalen et al. 2020 Aerosol and surface stability of HCoV-19 (SARS-CoV-6 2) compared to SARS-CoV-1 (RH 65%)

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No use of recirculation

• Virus particles in return ducts can also re-enter a building when centralized air handling units are equipped with recirculation sectors (may be in use at least in older all-air heating and cooling systems)

• Recirculation dampers should be closed (via the Building Management System or manually)

• Recirculation air filters are not a reason to keep recirculation dampers open as these filters do not filter out particles with viruses effectively since they have standard efficiencies and not HEPA efficiencies

• When possible, decentralized systems such as fan coil units that use local recirculation, also should be turned off to avoid resuspension of virus particles at room level (esp. when rooms are used normally by more than one occupant)

• If fan coils cannot be switched off because of heating/cooling needs, it is recommended that their fans are operated continuously because the virus can sediment in filters and resuspension boost can follow when the fan is turned on

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Filtration and air cleaners

• Outdoor air filters (filter class F7 or F8 or ISO ePM1) do not operate in the capture range of viruses – the size of a coronavirus particle of 80-160 nm (PM0.1) is smaller than the capture area of F8 filters (capture efficiency 65-90% for PM1)

• Outdoor air is not a source of viruses, thus no need to replace filters

• No need to clean ventilation ductworks as well

• In the case of air cleaners, to be effective, HEPA filter efficiency is needed

• Air cleaners with electrostatic filtration principles (not the same as room ionizers!) often work quite well too

• Because of limited airflow through air cleaners, the floor area they can effectively serve is normally quite small, typically less than 10 m2 – to be located close to breathing zone

• Maintenance personnel needs to apply common protective measures when replacing filters including respirators, because filters may have active microbiological material on them

15Summary of practical measures for HVAC operation1. Secure ventilation of spaces with outdoor air2. Switch ventilation to nominal speed at least 2 hours before the building usage time and switch

to lower speed 2 hours after the building usage time3. At nights and weekends, do not switch ventilation off, but keep systems running at lower speed4. Ensure regular airing with windows (even in mechanically ventilated buildings)5. Keep toilet ventilation 24/7 in operation6. Avoid open windows in toilets to assure the right direction of ventilation7. Instruct building occupants to flush toilets with closed lid8. Switch air handling units with recirculation to 100% outdoor air9. Inspect heat recovery equipment to be sure that leakages are under control10.Switch fan coils either off or operate so that fans are continuously on11.Do not change heating, cooling and possible humidification setpoints12.Do not plan duct cleaning for this period13.Replace central outdoor air and extract air filters as usually, acc. to maintenance schedule14.Regular filter replacement and maintenance works shall be performed with common protective

measures including respiratory protection

HVAC systems to reduce infectious disease transmission

5 August 2020

Prapoot Ponglaohapan PE, LEED AP, mASHRAETechnical Committee ACAT

MITR Technical Consultant Co.,Ltd.

1

References

• ASHRAE, 2020. ASHRAE Position Document on Infectious Aerosols

• Manuel Gameiro da Silva, Jarek Kurnitski, REHVA, 2020. Indoor Air Quality (IAQ) Concepts Case Study COVID-19

• Brent Stephens, NAFA, 2013. HVAC filtration and the Wells-Riley approach to assessing risks of infectious airborne diseases.

• S.-C. Chen, C.-M. Liao, 2007. Modelling control measures to reduce the impact of pandemic influenza among schoolchildren.

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References

• G. Buonanno, L. Stabile, L. Morawska, 2020. Estimation of airborne viral emission: quanta emission rate of SARS-CoV-2 for infection risk assessment.

• Hui Dai, Bin Zhao, 2020. Association of infected probability of COVID-19 with ventilation rates in confined spaces: a Wells-Riley equation based investigation.

• Chanjuan Sun, Zhiqiang Zhai (John), 2020. The efficacy of social distance and ventilation effectiveness in preventing COVID-19 transmission.

• Julia Collins, Nadia Abdelal. Spread of Disease

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Risks of airborne infectious diseases

Wells-Riley model (1978). based on a concept of

“quantum of infection,” = the rate of generation of infectious.

airborne particles (or quanta) can be used to model

the steady state well-mixed indoor environment, which people being exposed to the infectious particles and subsequently succumbing to infection.

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Wells-Riley equation (steady-state well-mixed)

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q = quanta generation rate (per hour)

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How many quanta infect susceptible

500 m2 (5,300 ft2) office building ; 24 workers + 1 infected workers

adults pulmonary ventilation rate 0.48 m3/hr

minimum outdoor air ventilation rate 450 cfm (750 m3/hr),

At 0.6 air changes per hourProbability of infected influenza virus = 40% (q = 100/hr).

= 9-10 workers acquire the flu virus (40% of 24 susceptible).

Change to 4 air change per hour Probability =8% ; 2 workers acquire the flu virus (8% of 24 susceptible)

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Reduce risk in Wells-Rilley model (Fennelly, Nardell, Nazaroff, Fisk)

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Non-steady state Wells-Rilley model (Gammaitoni, Nucci, Rudnick, Milton)

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Viral load

• 15% infectious droplet nuclei are in 0.3-1 µm particle

• 25% infectious droplet nuclei are in 1 - 3 µm particle

• 60% infectious droplet nuclei are in 3 - 10 µm particle

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Filter Efficiency

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Filter efficiency for virus

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Other parameters for 3 case studies

• Kdeposition = 0.7 per hour• Influenza = 100 quanta per hour• Tuberculosis = 13 quanta per hour• Rhinovirus = 5 quanta per hour• Adult pulmonary ventilation rate = 0.67 m3/hour• Child pulmonary ventilation rate = 0.50 m3/hour• ASHRAE Standard 62.1 for Office & School• ASHRAE Standard 170 for Hospital

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Kfiltration for Office (0.51 ACH-FA +1.52 ACH-RA)

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Kfiltration for School (2.7 ACH-FA +8.14 ACH-RA)

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Kfiltration for Hospital waiting room (2 ACH-FA +10 ACH-RA)

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The efficacy of social distance and ventilation effectiveness in preventing COVID-19 transmission

(Chanjuan Sun and Zhiqiang Zhai, 2020)

• What is the safe distance? (2-6 m)

• What is sufficient ventilation?

• The distance index = Pd ?

• The ventilation index = Ez ?

• Note: unknown “dose response” the model used actual case to calibrate the infectious dose (quantum of infection = 856.8/h)

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Distance of droplets

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Zone air distribution effectiveness (Ez) ASHRAE 62.1-2019

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Wells-Riley (pulmonary ventilation rate 0.3 m3/h)

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Modified Wells-Riley model with Pd & Ez

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Association of infected probability of COVID-19 with ventilation rates in confined spaces

(Hui Dai, Bin Zhao, 2020)

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Ro range 2.0 - 2.5 quanta = 14 – 48 /h

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No Mask Ventilation rate [100-350 m3/h for 15 minutes][1200-4000 m3/h for 3 hours] to ensure 1% infected

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Mask Ventilation rate [50-180 m3/h for 15 minutes][600-2000 m3/h for 3 hours] to ensure 1% infected

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8-11 กรกฎาคม 2563

Modelling control measures to reduce the impact of pandemic influenza among schoolchildren

(S.-C. Chen, C.-M. Liao, 2007)• Coupled the Wells-Riley equation and

the susceptible-exposed-infected-recovery (SEIR) model

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Influenza (68.67 quanta/hour)

Mask 80% + 1.5 ACH Ro = 1.06More Air Change = better

Good Mask = better

Modelling the progress of a 30-day influenza outbreak at an elementary school with a kindergarten. (a) We also represent the proportions of time-dependent infected number/total number because the population size is different between age groups. (b) Time-dependent infected number was estimated by the SEIR model. Parameter values: β=0·043, 0·082, 0·086, 0·094, and 0·011 for age groups 4–6, 7–8, 9–10, 11–12, and 25–45 years, respectively. 44

Impact of multiple measures on infected numbers in the 4–6 years age group. Control measures consider the situation without intervention and five integrated control methods including 80% vaccination coverage rate, 80% respiratory masking efficacy, and enhanced 1•5 ACH.

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Ro < 1

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“New Normal HVAC & Preventive Measures of COVID-19

in Public Buildings”

Mall & Department StoreBy

Prapoot Ponglaohapan PE, LEED AP, mASHRAEMitr Technical Consultant Co.,Ltd.

Technical Committee ACAT

131/7/2020 Department Store

3 Modes of transmission



Czechia=8,683 /Portugal=29,660 /Sweden=31,523 /worldometer 20May2020Czechia=16,371 /Portugal=50,868 /Sweden=81,100 /worldometer 31Jul2020


SARS-CoV-2 / quanta emission rates at viral load 100,000,000 copies/ml

31/7/2020 Department Store 5



Aalto University, the Finnish Meteorological Institute, the VTT Technical Research Centre of Finland

and the University of Helsinki.

modeled a space with aisles between shelves, typical grocery store.

The researchers simulated “cough,” spraying a cloud of aerosol particles smaller than 20 micrometers.

to observed how these particles moved throughout the simulated space.

• ..\8850.t.mp4


Thermal scan = eliminate riskQR check in = infection tracking



Cleaning & Touchless



UVC Mobile unit


Clean AHU & UVC lamp


Escalator, Air Conditioner Swab


Cinema deep clean


dimension of sars-cov-2 vs airborne particles

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