Various infectious diseases like SARS in 2003, Swine flu in 2009, MERS in 2012 and recently SARS-CoV-2 have challenged the health care providers across the globe. Quarantine and Isolation are an important mainstay of cluster containment. These measures help by breaking the chain of transmission in the community [1]. Several models of disease causation have been proposed. Among the simplest of these is the epidemiologic triad or triangle, the traditional model for infectious disease. The triad consists of an external agent, a susceptible host, and an environment that brings the host and agent together. In this model, the disease results from the interaction between the agent and the susceptible host in an environment that supports transmission of the agent from a source to that host [2]. Whereas the hospital may not have such control over the host factors and agents, the hospital certainly is responsible for the environment that surrounds the patients [3]. Controlling the environment is one of the major factors in handling any such crisis which plays a vital role in breaking the chain of transmission of infection. Air-conditioning and ventilation are such important environmental control measures, especially in the hospital area, which help in prevention and control over the infection. Healthcare facilities, both public and private are being prepared to take on this challenge of the COVID 19 Pandemic. Hence it is critical for hospitals to foresee the administrative issues to address the pandemic. Although the entire hospital has to be ready up to handle COVID patients, some areas have to be specifically geared for the purpose. These include the Flu Clinics for initial screening of suspected COVID cases, establishing Isolation Wards for confirmed COVID patients, as well as COVID ICUs/ HDUs for those who along with being positive is critically ill. Similarly, provision has to be made for the conduct of surgeries and deliveries of COVID positive patients. Besides this, the patient or his/ her specimen may be carried to different parts of the hospital for investigation or intervention, for which the general principles of awareness, patient masks, standard precautions including appropriate PPE and hand hygiene have to be followed.

The basic differences between air-conditioning for hospitals and other building types stem from the following characteristics(4): -

The scope of this document will be to provide safe ventilation for Flu Clinics, Isolation Wards, ICUs/ HDUs, and Operating Theatres.

(a) Flu Clinic.

It is the designated screening area for COVID-19 suspected cases, where the patient stays for a short time but the medical staff has to stay for an entire shift. Since the area has moderate risk and low occupancy, the primary aim of ventilation is dilution and removal of contaminants. Hence the Clinic should be established in a non-AC room, which has an adequate circulation of air & an effective exhaust system. If air-conditioning is required because of inclement weather, the room should be provided with a separate AC, preferably a split air-conditioner. The room should also have an effective exhaust system through windows and or exhaust fans.

(b) Isolation Ward.

The ward houses COVID positive patients with mild or moderate symptoms. Since the area has moderate risk and continued occupancy, the aim of ventilation are environment comfort, removal of contaminants, non-turbulent unidirectional airflow and prevention of leak of contaminated air to surrounding non-infected areas. Where the wards are not air-conditioned, installing an adequate number of exhaust fans may create dilution and removal of contaminated air, increased unidirectional airflow and negative pressure. However, it is to be ensured that the exhaust fans should not throw the exhausted air near an occupied building, public place or intake of air-conditioning plants.

In centrally air-conditioned areas, dedicated Air Handling Units (AHU) should supply air to Isolation wards. Since the droplet nuclei and viral particle may pass through the microfilters, the room air should not be recirculated and 100% fresh air should be pumped in. Blocking of return air vents may be implemented as an immediate measure before accommodating COVID positive patients. The dampers of the system should be adjusted to ensure that there is no recirculation of air and the outflow of air should be greater than the inflow, to maintain a negative pressure in the ward. The ward should have 12 air changes/ hour, the temperature should be maintained between 24^o + 2⁰ C & relative humidity at 40-60% [5].

Negative pressure in this system is to prevent leakage of contaminated air from ICUs into surrounding areas.

Doors and windows connecting to other rooms or corridors should be self-closing & sealed, to prevent leakage of contaminated air. An anteroom should always be established at the entrance to ICU to moderate the pressure change while opening doors. The area can also be used for donning of PPE and for documentation. The ICU should have 12 air changes/ hour supplied through a non-aspirating diffuser with the temperature and relative humidity to be maintained between 22-24^oC and 40-60% respectively [5].

The exhausted air should be let off into the atmosphere through an upward plume at a height of 3m above the tallest point of the building and at least be 25 feet away from air intakes or nearest inhabited areas [FIG-2] [5, 6]. In the hospital where this is not possible, ‘exhaust air treatment’ modalities should be built. The common ‘exhaust air treatment’ modality available is HEPA filtration of exhausted air [4-8].

Alternatively, exhausted air could be passed through chemical disinfection by using a diffused air aerator tank (non-metallic) containing 1% sodium hypochlorite solution or passing through a heated duct of more than 100⁰ C temperature for at least 3 seconds. Other modalities of ‘exhaust air treatment’ mentioned in literature are UV irradiation (254 nm) with an exposure time of 15min [6, 9-12].

The OT should have 15-20 air changes/ hour supplied through a non-aspirating diffuser with the temperature maintained between 22 + 2^oC and relative humidity between 40-60% [5]. (i) The exhausted air should be let off into the atmosphere through an upward plume at a height of 3m above the tallest point of the building and at least be 25 feet away from air intakes or nearest inhabited areas [5, 6]. Where this is not possible exhaust air should be treated through HEPA filtration or chemically disinfected by passing through 1% sodium hypochlorite solution or a heated duct of more than 100⁰ C temperature for at least 3 seconds [6, 9- 12].

Air conditioning is an essential component of HVAC system in most modern hospitals for patient and staff comfort, as well as infection control. However, in an environment of airborne infection like COVID, the air-conditioning system can itself spread the disease if not suitably controlled. The aim of air-conditioning in COVID facility should be to provide comfort for patients and staff, rapid removal of infection carrying particles, prevent recirculation of air, maintain a negative pressure from surroundings, and ensure safe disposal of exhaust air.

Negative pressure room Checklist