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Design and Construction Points for Negative Pressure Isolation Ward in International Standards

An isolation ward aims to control the airflow in the room so that the number of airborne infectious particles is reduced to a level that ensures cross-infection of other people within a healthcare facility is highly unlikely. This may be achieved by:

  • Control of the quantity and quality of intake or exhaust air

  • Maintain different air pressures between adjacent areas

  • Designing airflow patterns for specific clinical procedures

  • Diluting infectious particles with large air volumes

  • Air filtration – HEPA filters, etc.

Classification of Isolation Wards

Isolation ward can be classified as the infectious isolation ward and the protective isolation ward (the isolation ward for curing the mental disease). The infectious isolation ward is also termed as the negative pressure isolation ward. It is mainly used for prevention of the airborne disease from infecting both the environment outside the ward and the people except for the patient. In occasions when there is no infectious patient inside, the isolation ward can be used as the ordinary ward. This has been clearly specified in the standard of some nations. 

  • Neutral or standard room air pressure, for example standard air conditioning, also known as Class S

  • Positive room air pressure where an immune-compromised patient is protected from airborne transmission of any infection, Class P, including an Anteroom

  • Negative room air pressure, where others are protected from any airborne transmission from a patient who may be an infection risk, Class N, including an Anteroom

  • Negative room air pressure with additional barriers including an Anteroom, also known as Class Q for quarantine isolation.

Positive and Negative Air Pressure

negative air pressure

Recommended pressure gradients are: 

Type of PressurizationIsolation Room AnteroomEnsuite
Class S (Standard pressure)
Not requirde
Class N (Negative Pressure)- 10 Pa- 5 Pa- 15 Pa
Class P (Positive Pressure)+ 10 Pa+ 5 Pa

0 Pa

Where an isolation room is not provided with an Anteroom, the recommended minimum differential pressure between the isolation room and adjacent spaces should be 5 Pa. If however an Anteroom is provided, the recommended minimum differential pressure between isolation room and ambient pressure should be 10 Pa. 

ComponentStandard Pressure S
Standard Pressure N & Q
Standard Pressure P
AnteroomNot requiredYESYES
Ensuite (shower and toilet)YESYESYES
Hand basin with hands free operationYESYESYES

Pan Sanitiser

(disposables are acceptable as

alternative provision)


Required for Class Q

Optional for Class N

Self–closing door to roomYES
Grille flap to control room air flow-YES
Independent air supply-YES-
100% intake of fresh air-YES-
Low level exhaust 200mm above floor


HEPA filter on supply air--YES
HEPA filter on exhaust air-YES
Pressure monitoring-YESYES

Negative pressure rooms should be located at the entry to an Inpatient Unit, so that the patient requiring isolation does not need to pass other patient areas to access the Isolation Room. An Anteroom must be provided for a Negative Pressure Isolation Room. The air pressure in the Isolation Room must be lower than the adjoining rooms or the corridor. 

A dedicated exhaust system should be provided to the negative pressure isolation room. To maintain negative pressure the exhaust system removes a quantity of air greater than that of the supply air. The exhaust air duct should be independent of the building exhaust air system to reduce risk of contamination due to back draughts and should discharge away from staff, visitor and patient areas. The Isolation Room Ensuite exhaust should not be connected to the building toilet exhaust system.

A negative pressure Isolation Room requires the following:

An Anteroom that operates as an airlock with interlocking doors; both doors must not open at the one time; the Anteroom must be large enough to permit bed movement in and out of the Isolation Room if direct doors from corridor to Isolation Room is not provided.

Alarm to be activated on loss of differential pressure; time delay may be required to permit entry/exit from Isolation Room.

A clinical handwash basin with 'hands free' operation in the Isolation Room and the Anteroom. 

An Ensuite shower and toilet. Self-closing doors with interlocking doors to Anteroom. 

A HEPA filtration system provided to the supply air duct to protect patients from unfiltered air

Low level exhaust ducts approximately 200 mm above floor leve. 

Positive pressure Isolation Rooms may share a common air system, provided minimum outdoor air requirements comply with local regulations. A HEPA filter however must be fitted to the supply air inlet. A HEPA filter is not required to the exhaust air, as the exhaust air is not considered infectious. Differential air pressure instrumentation panels are required external to the Isolation Room in a prominent location (e.g.: adjacent to the entry door) The room requires labelling as a positive pressure Isolation Room.

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