Workplace Air Quality Calculator

No — those comfort-and-ventilation bands are common building-science rules of thumb for judging whether a space is getting enough fresh air, not regulatory exposure limits. The actual enforceable US occupational CO2 exposure limits (OSHA's permissible exposure limit and ACGIH's threshold limit value) are both 5,000 ppm as an 8-hour time-weighted average — literally 3-5 times higher than the range this calculator scores as 'poor.' Elevated indoor CO2 in an office setting is mainly a signal that ventilation may be inadequate, which correlates with stuffiness, odors, and reported drowsiness, not a direct toxicity concern at these concentrations.

These are the standard default outdoor air rates ASHRAE 62.1's ventilation rate procedure specifies for office-type spaces — a per-person component to dilute occupant-generated pollutants and a per-area component to address building material off-gassing and other area-based sources. They're real published values from that standard, and this calculator uses them directly rather than an invented approximation, though other space types (classrooms, retail, healthcare) have different ASHRAE 62.1 default rates than the office values used here.

It uses a steady-state mass-balance calculation: assuming each occupant generates a roughly constant amount of CO2 through normal breathing, the amount indoor CO2 rises above outdoor baseline (about 400 ppm) is inversely related to how much outdoor air is diluting it. This is a real, standard building-diagnostics technique for estimating actual ventilation rate from a CO2 reading — it becomes less reliable if the space hasn't reached a steady state yet (recently occupied, or occupancy has just changed) or if there are unusual CO2 sources beyond occupant breathing.

ASHRAE 62.1's ventilation formula includes both a per-person rate (to dilute pollutants people generate) and a per-area rate (to address off-gassing from building materials, furnishings, and finishes that occurs regardless of how many people are present). A large, sparsely occupied room can need meaningfully more total outdoor air than the occupant count alone would suggest, which is why this calculator combines both components rather than sizing ventilation off headcount alone.

The overall IAQ score weights CO2 at 40% and temperature comfort and humidity at 30% each — only the CO2 component is sourced from a published standard (ASHRAE 62.1 comfort/ventilation-adequacy bands, as described above). The temperature comfort range (roughly 21-24°C scoring highest) and humidity range (30-60% scoring highest) reflect commonly cited comfort guidance, but the specific point values and the 40/30/30 weighting are this calculator's own illustrative scoring model rather than a single published, standardized IAQ index — treat the composite score as a rough comparative estimate, not a certified indoor-air-quality rating.