THE VENTILATION NOTES
Ventilation notes
How published UK guidance and engineer logs treat a carbon dioxide number as a ventilation observation.
Where does HSE say a workplace carbon dioxide monitor should sit?
The HSE workplace page asks for a portable NDIR monitor at head height, more than 50 cm from people, and away from doors, windows and supply vents. A person breathing on the cell is not the room. Jeff Geerling and RevK wrote that case or board heat can raise the temperature reading. Those sentences are workplace guidance, not a home health rule. The still-life on this page is explanatory, and it is not a room this publication has checked.
Why is one carbon dioxide snapshot not the day?
HSE writes that a single snapshot can mislead and that persistently above 1500 ppm is a sign of poor ventilation, not a medical exposure limit. RevK’s closed British home office climbed from about 430 ppm at 09:00 to 1000 ppm after 14:00 with one person. A 1200 ppm screenshot can sit on the way up. That series is his. This publication has not published a room series, so these pages do not say a UK room needs a window opened.
| Reading | What the cited page uses it for |
|---|---|
| One snapshot | HSE says it can mislead. |
| Persistently above 1500 ppm | A workplace ventilation action, not a medical limit. |
| A published climb | The author’s room, not an AirMeasure UK series. |
- Head height, and more than 50 cm from people.
- Away from doors, windows and supply vents.
- Several readings through the day, not one snapshot.
Why does automatic baseline calibration assume about 400 ppm?
Yoctopuce’s calibration note says automatic baseline calibration assumes a room returns to about 400 ppm every few days, and that a continuously occupied room should switch it off. Adafruit repeats a 400 ppm outdoor figure for the SCD-30. RevK recorded outdoor air at 430–560 ppm and questioned forcing that zero. That outdoor band is his walk. These pages do not call 400 ppm the outdoor value, and they do not call an instrument calibrated.
Source-based notePlace the monitor where HSE already said
Head height, more than 50 cm from people, away from doors, windows and supply air. A case that runs warm is measuring its own heat as well as the room.
7 MIN READ ↗Source-based noteA snapshot is not the day
RevK’s closed office climbed for hours. HSE already says one reading can mislead, and that persistently above 1500 ppm is a ventilation action line — not a medical limit.
8 MIN READ ↗
Source-based noteABC assumes about 400 ppm
Automatic baseline calibration treats the lowest recent indoor point as fresh air near 400 ppm. RevK measured outdoor air at 430–560 ppm. A continuously occupied home office is the case Yoctopuce says should disable ABC.
8 MIN READ ↗