The evidence
What the research says — and where it stops.
OptiBreath exists because of a specific body of literature. Our customers are the kind of people who read primary sources, so this page gives you the papers, the effect sizes as reported, and the studies that undercut our own pitch. Decide for yourself.
The mechanism
Why a closed room fills up so fast.
A resting adult exhales roughly 20 litres of CO₂ an hour. In a 12 m² office with the door shut and no mechanical supply, that is enough to push the room from outdoor baseline past 1,000 ppm within about ninety minutes, and towards a steady state near 1,800 ppm by lunch.
The concentration follows a charging curve: it climbs quickly at first, then flattens as the rate of accumulation approaches the rate at which the room leaks air to the rest of the building. Where that curve flattens is set almost entirely by air changes per hour — which is why CO₂ is such a good proxy for ventilation, and why the same room can be fine with the door open and unacceptable with it shut.
Recovery is much faster than accumulation. Opening a window with any cross-breeze typically clears a small room in five to ten minutes. This asymmetry is the entire practical point of the instrument: the problem takes hours to develop and minutes to fix, but you cannot perceive either half of it without something that measures.
Humans have no chemoreceptor sensitive to CO₂ at these concentrations. What you notice at 1,600 ppm is that the room feels stuffy — and stuffiness is a response to humidity, temperature and body odour, not to the gas that the literature is actually about.
Exposure bands
The six bands, and where they come from.
These are the ranges OptiBreath classifies against. Each is anchored to a published exposure condition rather than an internal marketing threshold.
| Band | Range | What the literature reports | Typically |
|---|---|---|---|
| Baseline | 0–600 ppm | Effectively outdoor air. The reference condition against which every cognitive decrement in the literature is measured. | Outdoors, or a room with windows open and cross-ventilation. |
| Optimal | 600–800 ppm | No decision-making decrement reported. This is the band OptiBreath is designed to hold you in. | A well-ventilated office running at or above design airflow. |
| Elevated | 800–1,000 ppm | The threshold zone. Approaching the 1,000 ppm condition at which Satish et al. first measured statistically significant declines in complex decision-making. | A closed home office two hours into the working day. |
| Degraded | 1,000–1,400 ppm | At 1,000 ppm, six of nine decision-making measures fell moderately or substantially versus 600 ppm. Initiative and basic strategy were the most affected. | A meeting room with the door shut and four people in it. |
| Impaired | 1,400–2,500 ppm | Approaching the 2,500 ppm condition, where seven of nine measures fell and effect sizes on strategy and initiative were large. | A packed conference room, or a bedroom with the door closed overnight. |
| Critical | 2,500+ ppm | Large decrements across most decision-making measures, alongside the drowsiness, headache and loss of focus commonly reported at these concentrations. | A sealed room at capacity with mechanical ventilation off or failed. |
Common ground
Four things nobody in this field disputes.
Before the contested part, it is worth being clear about how much is settled. Everything below is accepted by both the researchers who found large cognitive effects and the ones who could not replicate them.
- 01
Indoor CO₂ is a reliable, real-time indicator of ventilation rate per occupant. That much is uncontested.
- 02
Low ventilation rates are independently associated with worse reported symptoms, higher absence and reduced performance.
- 03
Concentrations above 1,000 ppm indicate ventilation below the rate most standards target for occupied spaces.
- 04
You cannot perceive CO₂ at these concentrations. Without an instrument you have no idea which band you are in.
References
The papers.
Cited with the effect sizes as the authors report them, not as we would prefer them.
- Chamber study2012
Is CO₂ an Indoor Pollutant? Direct Effects of Low-to-Moderate CO₂ Concentrations on Human Decision-Making Performance
Satish, U., Mendell, M. J., Shekhar, K., Hotchi, T., Sullivan, D., Streufert, S., & Fisk, W. J.
Environmental Health Perspectives, 120(12), 1671–1677
In a controlled chamber study using the Strategic Management Simulation battery, moderate to large decrements appeared in six of nine decision-making measures at 1,000 ppm and seven of nine at 2,500 ppm, relative to a 600 ppm baseline. Initiative and basic strategy showed the largest effects.
DOI 10.1289/ehp.1104789 - Chamber study2016
Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, and Volatile Organic Compound Exposures in Office Workers (the COGfx Study)
Allen, J. G., MacNaughton, P., Satish, U., Santanam, S., Vallarino, J., & Spengler, J. D.
Environmental Health Perspectives, 124(6), 805–812
Across a double-blind, controlled exposure of 24 professionals over six days, cognitive function scores averaged 61% higher on Green building days and 101% higher on Green+ (enhanced ventilation) days than on Conventional days. Scores fell roughly 15% for each 400 ppm increase in CO₂.
DOI 10.1289/ehp.1510037 - Field study2017
The impact of working in a green certified building on cognitive function and health
MacNaughton, P., Satish, U., Laurent, J. G. C., Flanigan, S., Vallarino, J., Coull, B., Spengler, J. D., & Allen, J. G.
Building and Environment, 114, 178–186
A field study of workers in green-certified versus non-certified buildings found 26.4% higher cognitive function scores and 6.4% higher sleep quality scores among occupants of green-certified buildings — moving the finding out of the chamber and into real offices.
DOI 10.1016/j.buildenv.2016.11.041 - Economic analysis2015
Economic, Environmental and Health Implications of Enhanced Ventilation in Office Buildings
MacNaughton, P., Pegues, J., Satish, U., Santanam, S., Spengler, J., & Allen, J.
International Journal of Environmental Research and Public Health, 12(11), 14709–14722
Doubling outdoor air ventilation rates was estimated to cost less than $40 per person per year while producing productivity gains valued at roughly $6,500 per person per year — a return of two orders of magnitude.
DOI 10.3390/ijerph121114709
What we do not claim
The case against our own product.
Any company selling an instrument on the strength of a contested literature owes you this section. Here is what argues against the strong version of our pitch.
Papers that cut against us
- Argues against us2019
Do Indoor CO₂ Levels Directly Affect Perceived Air Quality, Health, or Work Performance?
ASHRAE Journal, 61(9), 70–77
A review — co-authored by the lead author of the 2012 chamber study — concluding that the evidence for direct effects of CO₂ at concentrations below about 5,000 ppm is inconsistent, and that several attempts to replicate the strongest findings did not succeed.
Read the paper - Argues against us2017
Effects of exposure to carbon dioxide and bioeffluents on perceived air quality, self-assessed acute health symptoms, and cognitive performance
Indoor Air, 27(1), 47–64
Exposure to pure CO₂ at 3,000 ppm produced few effects on cognitive performance, while exposure to bioeffluents at the same CO₂ level increased reported health symptoms and reduced motivation — suggesting CO₂ may act partly as a proxy for everything else people exhale.
DOI 10.1111/ina.12284
Our position, stated plainly
- The strongest effects come from controlled chamber studies with small samples. Several independent replication attempts have not reproduced them at the same magnitude.
- CO₂ may be partly a proxy rather than a pure cause. It correlates tightly with ventilation rate, bioeffluents and VOC accumulation, and some studies find effects only when those travel together.
- Effect sizes vary by task. Complex, open-ended, strategic work shows larger decrements than simple reaction-time or recall tasks — which is precisely the work our customers do.
- Individual response varies. The right way to use OptiBreath is to correlate your own environment against your own output, not to apply a population average to yourself.
- We report the indicative decision-making index as a directional guide derived from published effect sizes. It is not a clinical measurement and we do not present it as one.
The honest summary: the measurement is solid and useful, the ventilation link is uncontested, and the size of the cognitive effect is still being argued about. We would rather you buy the instrument understanding that than return it in sixty days feeling misled.
Read all that and still want one?
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