Airborne Infectious Diseases - ashrae-london.com · •ASHRAE does not provide specific requirements for infectious disease control in schools, prisons, shelters, transportation,

09/03/2020

Prof Ljubomir Jankovic 1

Prof Ljubomir Jankovic

Professor of Advanced Building Design, University of HertfordshireChapter President 2019-2020, ASHRAE UK London & SE Chapter

Airborne Infectious DiseasesASHRAE Position Document

Part of ASHRAE COVID-19 Preparedness Resources

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Presentation scope

To reference ASHRAE resources in the context of the COVID-19 outbreak

To provide an overview of ASHRAE's approved position document on Airborne Infectious Diseases, relating to the operation of heating, ventilating and air-conditioning systems

To discuss practical implications for building owners, operators, and engineers

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Online resources

The ASHRAE COVID-19 Preparedness Resources webpage: https://www.ashrae.org/technical-resources/resources

Including ASHRAE's approved position document onAirborne Infectious Diseases

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ashrae.org/COVID19 resources

“ASHRAE's COVID-19 Preparedness Resources are available as guidance to building owners, operators and engineers on how to best protect occupants from exposure to the virus, in particular in relation to airborne particles that might be circulated by HVAC systems”2019-20 ASHRAE President Darryl K. Boyce

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https://www.ashrae.org/technical-resources/resources

09/03/2020


ashrae.org/COVID19 resourcesThe preparedness resources page contains a variety of documents:

Guidance documentsContacts for relevant technical committeesASHRAE publicationsReferences to ASHRAE Handbook ContentRelevant journal papersASHRAE Standards and GuidelinesVideos…and others

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ashrae.org/COVID19 resources

We will focus on:

ASHRAE's approved position document onAirborne Infectious Diseases

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Airborne Infectious Diseases position document (PD)Information on the following:• the modes of transmission of airborne infectious diseases

• the implications for the design, installation, and operation of heating, ventilating, and air-conditioning (HVAC) systems

• the means to support facility management and planning for everyday operation and for emergencies

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Airborne Infectious Diseases PD

• The PD covers the spread of infectious disease by small airborne particles (an aerosol) that contain microorganisms

• The PD does not cover transmission via direct contact with individuals or surfaces

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Higher transmission rates within 1 to 2 m(risk zone 6-8 m?)

Diagram of aerosol movement

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Airborne Infectious Diseases PDDegree of exposure to airborne infection

D = I ⋅ q ⋅ p ⋅ t / Q I – number of infectorsq - number of doses of airborne infection

p - pulmonary ventilation per person

t – exposure timeQ – volume of fresh or disinfected air

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Airborne Infectious Diseases PDWells-Riley standard model of airborne infection

C = S(1 – e–Iqpt/Q)

C – number of new infections

S – number of susceptiblesI – number of infectors – reducing I (people density) decreases exposure

q - number of doses of airborne infection – reducing q (2m distance) decreases exposure

p - pulmonary ventilation per person – individual

t – exposure time – reducing t (duration in high density areas) decreases exposure Q – volume of fresh or disinfected air - increasing Q decreases exposure

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degree of exposure to infection

probability of a single infection

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0.10 0.10

0.99 0.63



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Practical implications forbuilding owners, operators, and engineers• transmission through HVAC systems must be considered

• HVAC systems may contribute to both to transmission of disease…

• …and, potentially, to reduction of transmission risk

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Practical implications forbuilding owners, operators, and engineersVarying Approaches for Facility Types:• health-care facilities have criteria for ventilation design to

mitigate airborne transmission of infectious disease

• but most infections are transmitted in ordinary occupancies

• ASHRAE does not provide specific requirements for infectious disease control in schools, prisons, shelters, transportation, and other public facilities

• general ventilation and air quality requirements of Standards 62.1 and 62.2 apply

• this position document applies to all these facilities

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Practical implications forbuilding owners, operators, and engineersVentilation and Air-Cleaning Strategies:

• supplying clean air to susceptible occupants

• containing contaminated air and/or exhausting it to the outdoors

• diluting the air in a space with cleaner air from outdoors

• cleaning the air within the room

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• dilution ventilation

• laminar and other in-room flow regimes

• differential room pressurization

• personalized ventilation

• source capture ventilation

• filtration (central or unitary)

• upper room ultraviolet germicidal irradiation (UVGI)

• Note: the UV radiation needs to be in the UV-C spectrum with wavelength of 100-280 nm, which deactivates or destroys RNA and DNA

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• ventilation represents a primary infectious disease control strategy through dilution of room air

• highly efficient particle filtration is likely to reduce the airborne infectious particles

• directed supply and/or exhaust ventilation is important in several settings, including operating rooms

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Breathing, coughing and sneezing (non-ASHRAE)

2m6m

8m

BreathingCoughingSneezing

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Dilution

Filtration

100%

Cough-generated droplets 0.65 μm to 3.3 μmExhaled breath droplets: 80% in range 0.3 μm - 1 μmCorona virus size 0.12 μm is contained in dropletsHEPA filters eliminate 99.95% of droplets size ≥ 0.3 μmUV radiation can be combined with filtering

< 100%

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Unidirectional lowvelocity flow

High velocityturbulent flow

~

~

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• energy-conserving strategies, including demand controlled ventilation should be used with caution

• natural ventilation by user-operable windows, is not covered as a method of infection control by most ventilation standards and guidelines

• …but it does help in the absence of other measures

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• room pressure differentials are important for controlling airflow between areas in a building

• airborne infection isolation rooms (AIIRs) are kept at negative pressure with respect to the surrounding areas

• hospital rooms with immune-compromised individuals are kept at positive pressure in protective environments

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Practical implications forbuilding owners, operators, and engineers

negative pressure positive pressure

airborne infection isolation rooms

surrounding rooms

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positive pressure

rooms with immune-compromised individuals

surrounding rooms

negative pressure

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• personalised ventilation systems supplying 100% highly filtered or UV disinfected air may be protective

• there are no known field studies that justify the efficacy

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Practical implications forbuilding owners, operators, and engineersTemperature and Humidity:• ASHRAE PD refrains from making a universal recommendation• evidence that controlling relative humidity (RH) can reduce

transmission of certain airborne infectious organisms• lower humidity change droplets into droplet nuclei and make

them fall on the floor• evidence of lower inhalation of droplets at higher RH• breathing dry air could cause desiccation of the nasal mucosa and

susceptibility to respiratory virus infections• no sufficient evidence that maintaining temperature and RH

reduces airborne survival

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Non-HVAC Strategies:

• allowing and encouraging employees to stay at home when ill is more effective than any HVAC interventions

• prompt identification of patients with illness and use of respiratory hygiene source control

• high-efficiency personal protective equipment may be considered (N95 respirators remove 95% of ≥ 0.3 μm particles)

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Practical implications forbuilding owners, operators, and engineersEmergency Planning:

• increasing dilution ventilation, increasing relative humidity, or quickly applying upper room UVGI, provided that this does not create either

• flow of air to less contaminated areas or

• conditions of extreme discomfort

• creating pressure differentials may be the appropriate strategy

• actions should be undertaken in collaboration with infection control professionals

• knowledge of the system operation and the nature and source of the threat are important

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Recommendations• all facility designs should follow the latest practice standards

• commissioning, maintenance, and proper operation of buildings, and systems for controlling airborne infectious disease, are necessary for buildings and systems to be effective

• enhancing well designed, installed, commissioned, and maintained HVAC systems with supplemental filtration, UVGI, and increased ventilation

• filtration and UVGI can be applied quickly at moderate additional cost

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RecommendationsHealthcare infrastructure needed to quickly respond to a pandemic in emergency wards, admissions, waiting rooms, crowded shelters:

• HVAC systems that separate high-risk areas

• HVAC system capacity to upgrade filtration

• the ability to increase ventilation as high as 100% outdoor air

• the ability to humidify air

• the ability to enable effective upper-room UVGI at the upper room and ceiling heights of at least 2.4 m

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Recommendations• infection control strategies should always include multiple

interventions (not just ventilation).

• multidisciplinary teams of engineers, building operators, scientists, infection prevention specialists, and epidemiologists should collaborate

• to identify and implement interventions and

• to understand the uncertainty of the effectiveness of current practice recommendations

• building operators and engineers have a role to play in planning for infectious disease transmission emergencies

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RecommendationsStandards and guidelines should strengthen requirements for the following:

• improved particle filtration for central air handlers

• upper-room and possibly other UVGI interventions and electrical infrastructure to quickly deploy them

• the ability to quickly and temporarily increase the outdoor air ventilation rate

• avoiding lower ventilation levels motivated solely by reduced energy consumption

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Recommendations• researchers should receive input from many discipline experts

• controlled intervention studies should be conducted

• to quantify disease propagation resulting from various ventilation rates

• to quantify the relative airborne infection control performance and cost-effectiveness of specific engineering controls individually and in field applications

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RecommendationsResearch should

• quantify rates of airborne removal by filtration and inactivation by UVGI strategies specific to individual microorganisms

• field validate in real facilities the effectiveness of these interventions in preventing transmission

• be conducted to better characterize the particle size distributions of coughed materials (a broad range of diameters)

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More informationThis presentation was an overview with some of my personal professional interpretations.

For the original source, please consult the following for further details:

COVID-19 (CORONAVIRUS) PREPAREDNESS RESOURCES

https://www.ashrae.org/technical-resources/resources

including

ASHRAE Position Document on Airborne Infectious Diseases

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Other relevant information (non-ASHRAE)Evaporation and dispersion of exhaled droplets in stratified environment: https://iopscience.iop.org/article/10.1088/1757-899X/609/4/042059/pdf

Some questions on dispersion of human exhaled droplets in ventilation room: answers from numerical investigation: https://onlinelibrary.wiley.com/doi/full/10.1111/j.1600-0668.2009.00626.x

Origin of Exhaled Breath Particles from Healthy and Human Rhinovirus-Infected Subjects: https://www.liebertpub.com/doi/10.1089/jamp.2010.0815

Particle Size Concentration Distribution and Influences on Exhaled Breath Particles in Mechanically Ventilated Patients: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0087088

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https://iopscience.iop.org/article/10.1088/1757-899X/609/4/042059/pdf

https://onlinelibrary.wiley.com/doi/full/10.1111/j.1600-0668.2009.00626.x

https://www.liebertpub.com/doi/10.1089/jamp.2010.0815

https://journals.plos.org/plosone/article%3Fid=10.1371/journal.pone.0087088

09/03/2020


Thank you for listeningProf Ljubomir Jankovic

University of Hertfordshire

[email protected]

You can find these slides on:http://www.ashrae-london.com/latest.html

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Airborne Infectious Diseases - ashrae-london.com · •ASHRAE does not provide specific requirements for infectious disease control in schools, prisons, shelters, transportation,