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From Air Removal to Infection Control: Rethinking Hospital Exhaust System Design

Yaseen Khan Mohammed CEng

The COVID-19 era exposed critical gaps in how we manage airborne infection risks in healthcare facilities.

Most current codes strongly emphasize indoor air quality — ventilation rates, filtration, and pressure control — yet there appears to be comparatively limited guidance on the treatment of contaminated exhaust air before it is discharged into the atmosphere.

Research indicates that microorganisms from areas such as isolation rooms, laboratories, dental suites, and decontamination spaces can survive under certain environmental conditions and, in poorly designed exhaust configurations, may pose potential exposure risks — particularly in dense urban environments.

This raises an important question:
Should hospital exhaust systems be considered a formal part of infection control strategies, rather than merely air removal systems?

Technologies such as HEPA filtration, UV disinfection, and controlled exhaust discharge design are already applied in laboratories and high-risk facilities.

Is it time for similar risk-based approaches to be incorporated into healthcare ventilation codes and standards?

I’m interested to hear from fellow HVAC engineers, infection control specialists, and code professionals:
 Point right Have you encountered projects where exhaust air treatment was required or debated?
 Point right Do you see current standards as sufficient, or is there a gap that needs to be addressed?

  • If the air being sucked out of a hospital ward is so hazardous that it needs disinfection, then what does that mean for the people inside that hospital?

  • This sort of thing has been mentioned before, last sentence:-

    "The very first canon of nursing, the first and the last thing upon which

    a nurse's attention must be fixed, the first essential to a patient,

    without which all the rest you can do for him is as nothing, with which
I had almost said you may leave all the rest alone, is this: TO KEEP THE
AIR HE BREATHES AS PURE AS THE EXTERNAL AIR, WITHOUT CHILLING HIM. Yet
what is so little attended, to? Even where it is thought of at all, the
most extraordinary misconceptions reign about it. Even in admitting air
into the patient's room or ward, few people ever think, where that air
comes from. It may come from a corridor into which other wards are
ventilated, from a hall, always unaired, always full of the fumes of
gas, dinner, of various kinds of mustiness; from an underground kitchen,
sink, washhouse, water-closet, or even, as I myself have had sorrowful
experience, from open sewers loaded with filth; and with this the
patient's room or ward is aired, as it is called--poisoned, it should
rather be said. Always, air from the air without, and that, too, through
those windows, through which the air comes freshest. From a closed
court, especially if the wind do not blow that way, air may come as
stagnant as any from a hall or corridor."
    Notes on Nursing, 1860, Chapter 1
  • in reply to Simon Barker

    Codes and guidelines such as ASHRAE 170, CDC, WHO, and HTM comprehensively address indoor air quality within hospital environments.

    ASHRAE, in particular, emphasizes maintaining differential pressure relationships between critical and non-critical spaces to prevent contaminated air from migrating into occupied areas and to effectively contain infections. Various pressure sensing and monitoring technologies are widely implemented to control these environments, with alarm systems to alert facility teams in case of pressure failure. This approach is routinely applied in isolation rooms, laboratories, operating theatres, and other high-risk areas.

    Additionally, HEPA filtration systems are strategically installed to further limit the spread of airborne contaminants within hospital buildings.

    In conclusion, while the quality and control of air inside healthcare facilities are thoroughly regulated and addressed by existing codes, the treatment and risk management of contaminated exhaust air discharged to the atmosphere receive comparatively limited consideration.

  • in reply to Simon Barker

    It probably means that some of the people inside the hospital are sick (rhetorical statement of the 'should be obvious').

    Such extraction systems essentially concentrate all the risks/hazards of the whole hospital into a single location/region/flow that could them be a vector for illness. It's why the 'west end' of major industrial cities (where the fresh air comes from) have the big houses for the wealthy, and the 'east end' is for the poor poverty stricken workers have to live breathing the efflux of their industry..

    Think asbestos carried on the wind, or the siting of sewage treatment works (see also Shieldhall..)

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