By Eamonn Ryan
For decades, indoor air quality standards were built on a hazards-based framework: identify contaminants and assign maximum allowable concentrations. If each limit was met, the environment was deemed safe.
This gap led researchers to seek a more comprehensive metric. frimufilms/Freepik
But this approach contains a fundamental flaw – people are exposed to mixtures of pollutants, not single substances in isolation.
The limits of the hazard model
Contaminant limits often reflect political compromise as much as science. More importantly, compliance does not necessarily equal low risk. An environment may meet every individual threshold yet still produce significant cumulative harm.
This gap led researchers to seek a more comprehensive metric.
The harm-based framework
Advances in public health introduced Disability-Adjusted Life Years (DALYs), a metric combining years of life lost and years lived with disability. DALYs allow comparison across different diseases and exposures.
Applied to indoor air, this framework enables a new question: How much total harm does indoor air cause – and how can ventilation reduce it most effectively?
Analyses reveal that only a small group of pollutants dominate health impacts in residential buildings:
- PM₂.₅
- Formaldehyde
- Nitrogen dioxide
Among these, particulate matter accounts for the majority of harm. Because particles are highly filterable, enhanced filtration becomes a powerful tool – often more energy-efficient than simply increasing outdoor air supply.
A new standard for practice
The updated ASHRAE Standard 62.2 reflects this thinking. Instead of prescribing ever-increasing airflow, it balances:
- Baseline ventilation for comfort
- Targeted intervention when health-based harm thresholds are exceeded
This approach avoids over-ventilation while directly addressing measurable risk.
Toward integrated infection control
The same framework could extend to infectious aerosols. ASHRAE Standard 241 addresses epidemic conditions, but future integration may place pathogens such as influenza or COVID-19 within the same quantified harm model.
The result is a coherent, science-based strategy: design for comfort, measure for health, and optimise systems to reduce total harm – not just meet prescriptive limits.
Source: ASHRAE Guidance and Research Initiatives
