Indoor Air Quality Assessment and Investigation
The investigation sequence
IAQ work follows a logical progression: collect complaints and history → walkthrough → hypothesis formation → targeted sampling → interpretation → recommendations. Sampling without a hypothesis is the cardinal error; it produces data no one can interpret.
Concepts a candidate must know
- Building characterization: HVAC type, outdoor air supply, occupancy, recent renovations, water events, and occupant activities.
- Complaint patterns: symptoms tied to time and place (worse in a specific zone, better away from the building) point to source or ventilation issues; symptoms unrelated to the building suggest other causes.
- Comfort parameters: temperature, relative humidity (roughly 30–60% RH is a common comfort target), CO₂ as a ventilation indicator (outdoor ~420 ppm; elevated indoor levels suggest inadequate ventilation, not a pollutant itself).
- Contaminant categories: biological (mold, allergens), chemical (VOCs, formaldehyde, CO), particulate, and combustion byproducts.
- Instrumentation limits: real-time meters are screening tools; laboratory methods provide defensible quantification.
Traps
Questions often present a single elevated CO₂ reading as proof of "poor air quality" - CO₂ is a proxy for ventilation, not a toxicant. Another trap conflates odor with hazard, or treats one grab sample as representative of a whole building.
Rule of thumb
Investigate from general to specific: building-level data first, then zone-level, then source-level. Never sample a contaminant you cannot interpret against a health-based or consensus benchmark.
Worked example
Occupants in one wing report afternoon headaches. Walkthrough shows that wing's air handler running with minimal outdoor air during peak occupancy. Correct response: log CO₂ over an occupied day, verify outdoor-air damper position, and recommend ventilation correction before any chemical sampling.