IAQ Design – switch towards harm-based metrics

Historically, building standards have been founded on established air quality metrics mainly based on concentrations of contaminants. However, there is a potential change on the horizon, as articulated in the recent report from the ASHRAE Standing Standard Project Committee on Ventilation and Acceptable Indoor Air Quality in Residential Buildings (62.2). Simon Jones (above), founder, Air Quality Matters, analyses its implications.

Understanding the new addendum
The core development introduced by ASHRAE 62.2 is the potential addendum proposing a “harm-based indoor air quality procedure” as an alternative method of compliance. In layman’s terms, rather than solely measuring and managing the concentration of indoor air pollutants, this addendum would incorporate the actual harm these pollutants may cause. To the traditional engineer, this marks a shift in understanding and addressing indoor air quality. Where once the challenge was primarily measuring quantities (how much of a pollutant is present?), it now spans into understanding and mitigating qualitative impacts (how harmful is the pollutant to the building occupants?).

Harm-based v. level-based metrics
To truly grasp the implications of this new proposal, it is essential to understand the difference between harm-based and traditional level-based metrics of IAQ. Airborne contaminants have various origins – from internal sources like building materials and furnishings to external sources brought in by ventilation. Exposure to these contaminants depends on their concentration and the time a person spends in that environment. Notably, every individual reacts differently to these exposures based on their metabolic rate, physiology, age and sex.

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