COMMENTARY ONLINE EXCLUSIVE

Optimising airborne infection control through ventilation design

Ng Teng Fong General Hospital; image by CPG Consultants Pte Ltd

By Anisa Pinatih

Learning from previous outbreaks in the past and the current COVID-19 pandemic, architects and designers have been leading hospital design to evolve in a way that seeks to further facilitate treatment, minimise spread and protect medical service providers. Aside from optimising spatial layout and facilities provision, attention should also be paid to ventilation design. This is important because, in some cases, transmission is airborne, which puts healthcare workers in a more vulnerable position.

AIRBORNE TRANSMISSION
Building ventilation systems can reduce the proliferation of micro-organisms—fungi, bacteria and viruses—into the spaces because it can regulate air flows that reduce moist and dampness. This is especially important since many disease transmissions are airborne, such as mycobacterium tuberculosis that causes TBC in humans and rubeola virus that causes measles.

Whether or not the novel coronavirus can be easily transmitted in the same way is a question yet to be answered by empirical research. WHO claims that droplets are relatively heavy so they do not travel far and quickly sink to the ground. But as an infected person coughs, the virus travels in liquid particles, varying in size (ranging from visible droplets to microscopic aerosol particles), which in turn affects how long the virus will stay in the air.

Research on viral shedding of COVID-19 is still developing. Some indicate that airborne isolation may be needed in hospitals only, while some believe that the transmission is indeed airborne—with evidence coming from high infection rates in a conference room and a bus, whose central air-conditioners were in indoor recirculation mode. Either way, evidence on aerosol transmission thus far suggests that infection is higher in closed environments because the lack of airflow may cause viral contamination to float longer in the air (research suggests that such aerosols may linger up to three hours or longer).

To optimise airbone disease infection control, ventilation should be an integral part of hospital design; image by sevasaves1/Shutterstock

Although more evidence is needed, recent scientific brief from WHO acknowledges that airborne transmission is possible in specific circumstances and settings, such as in medical procedures that generate aerosols like endotracheal intubation, bronchoscopy, open suctioning, administration of nebulized treatment, and so on.

VENTILATION SYSTEMS & AIRBORNE DISEASES PREVENTION
In tropical countries, hospital doors and windows are often sealed. In the case of airborne diseases, this poses more risk because split air-conditioners are designed to move the heat out and not bring the outside fresh air in. This system does not facilitate the required hourly air changes that would help to prevent viral aerosol spread.

Research suggests that certain ventilation systems can be utilised in airborne disease prevention. The first is high-efficiency particulate air (HEPA) filtration, by which microbes will be filtered through grating and prevented from travelling further. The downside of this system is that it could be costly and, if not cleaned properly, may turn into a breeding spot. The second is ultraviolet disinfection, which will kill all micro-organisms in the space, but it is also a costly technology and only works for the upper level of the room. The third is dilution ventilation, which will dilute microbe concentrations by flushing them with outdoor air. The problem with using this system is the risk of flushing in polluted urban air that can be dangerous for respiratory cases.

NEGATIVE PRESSURE VENTILATION
Learning from the SARS outbreak, Dr Fatimah Lateef from Singapore General Hospital maintains that diluting droplet nuclei in the air is the most important engineering control in minimising airborne infections. Ventilation, therefore, should be an integral part of hospital design. Rooms dedicated for airborne diseases should have negative pressure, which means that the exhaust rate should be significantly higher than the supply rate.

Rooms where severe cases are treated should be negatively pressurised, with exhaust rate exceeding the air supply rate by a generous margin; image by Sucharas Wongpeth/Shutterstock

If this feature is to be applied in new/other hospitals, special attention should be paid to the possibility of high turbulence. Consulting ventilation engineers during the planning and the construction phase is important to decide on the precise amount of flow. Another important factor is the incorporation of an antechamber or vestibule design to minimise the escape of contaminated air during the opening and closing of doors.

In Singapore General Hospital, patients with severe symptoms are treated in critical areas with two end rooms with negative pressure ventilation and heavy lead doors. The observation unit in the emergency department has isolation rooms with doors fitted with a self-closing device. For isolation rooms with no negative pressure ventilation, optimum air circulation with adequate fresh air exchange is ensured.

NATURAL VENTILATION
Research has shown that the severity of symptoms of COVID-19 cases varies. Negative pressure ventilation may be needed in a room where an aerosol-generating medical procedure is performed. For mild to moderate cases, this may not be the case. Although patients may still be coughing and sneezing, they do not need nebulised treatment or intubation that may increase the risk of airborne transmission. However, precautions still need to be taken to lower the risk of infection.

Governments in Asia require hospitals and healthcare facilities to improve their ventilation systems, not only in rooms where severe cases are being treated, but also corridors and other common areas. Aside from reducing the risk of transmission, a good ventilation system in a building will also have a positive impact on the well-being of the patients.

Ng Teng Fong General Hospital has an open floor plan with small wings for each room, which lends each patient a corner with an operable window that allows natural breeze to flow in. The exterior has abundant shading elements, including a series of planting, precast concrete overhangs, and vertical sunshades that lower the temperature of incoming air before it reaches the rooms.

The wing design at Ng Teng Fong General Hospital optimises its natural ventilation system; image by CPG Consultants Pte Ltd

Aabenraa Hospital in Denmark is another example of a facility that successfully improves its rooms’ quality by enhancing natural ventilation. Airflow is optimised through controlled natural ventilation, while taking advantage of local climate conditions and a supportive courtyard design. There are fresh air inlets at the bottom of the exterior walls that allow outdoor air to pass through the basement. The air acquires a constant lower temperature before entering the common areas; then passes through a particle filter and a convector element before entering the rooms. Cowls on the roof and the natural wind that passes above it creates lower pressure. This triggers air movement that exhausts air in the rooms naturally. Fans can also be used to help pump out the indoor air if necessary. Overall, the system is able to ensure that the air-change rate is sufficient to optimise infectious disease control.

CONCLUSION
Knowledge about COVID-19 and the ways it is transmitted is developing quickly. What was known two months ago might just be a fraction of the bigger picture. The diagnostic symptoms have expanded from cough and pneumonia to intestinal problem and abdominal pain. Transmission, as it turns out, is not only by close contact and contaminated surfaces, but might also be airborne.

Architects and designers play a key role in creating built spaces and infrastructures that can minimise the spread. In hospitals, healthcare workers are particularly vulnerable when treating severe cases. Designing ventilation strategies and systems that can reduce the risk is important. The future of hospital design might be forever changed by COVID-19 where the priority may no longer just be indoor thermal comfort, but minimising health risk and maximising safety.

– Construction+ Online 

 

 

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