Extech CO250 Portable Indoor Air Quality CO2 Features:
- Checks for Carbon Dioxide (CO2) concentrations
- Calculates statistical weighted averages of TWA (8 hour time weighted average) and STEL (15 minute short term exposure limit)
- Maintenance free NDIR (non-dispersive infrared) CO2 sensor
CO2 Guidelines:
Non-Enforced Reference levels:
- 250 – 350 ppm – background (normal) outdoor air level
- 350- 1,000 ppm – typical level found in occupied spaces with good air
- 1,000 – 2,000 ppm – level associated with complaints of drowsiness and poor
- 2,000 – 5,000 ppm – level associated with headaches, sleepiness, and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate and slight nausea may also be
- >5,000 ppm – Exposure may lead to serious oxygen deprivation resulting in permanent brain damage, coma and even
Regulatory exposure limits: ASHRAE Standard 62-1989: 1000ppm: CO2 concentration in occupied building should not exceed 1000ppm. OSHA: 5000ppm: Time weighted average over five 8-hour work days should not exceed 5000ppm Building bulletin 101 (Bb101): 1500ppm. UK standards for schools say that CO2 at averaged over the whole day(i.e. 9am to 3.30 pm) should not exceed 1500ppm. Germany, Japan, Australia, UK…: 5000ppm, 8 hours weighted average in occupational exposure limit is 5000ppm.
Extech CO250 Specifictions:
| Function | Range | Resolution | Accuracy |
| CO2 | 0 to 5000ppm | 1ppm | ±(%5rdg + 50ppm) |
| 5000 to 9999ppm | 1ppm | Not specified | |
| Pressure dependence: +1.6% reading per kPa deviation from normal pressure, 100kPa | |||
| Temperature | -10 to 60°C 14 to 140°F | 0.1° | ±0.6°C/0.9°F |
| Humidity | 0.0 to 99.9% | 0.1% | ±3%(10 to 90%) ±5%(< or > 10 to 90%) |
| Wet Bulb | -5 to 60°C 23 to 140°F | 0.1° | Calculated from RH and Temperature |
| Dew Point | -20 to 60°C -4 to 140°F | 0.1° | |
Display Triple LCD with backlight Sensor Type
- CO2: NDIR (non-dispersive infrared) technology
- Humidity: Capacitance sensor; Temperature (air): Thermistor
Operating Conditions 0 to 50C (32 to 122F); < 95% RH non-condensing
Storage Conditions -20 to 60C ( -4 to 140F); <99% RH non-condensing
Power Supply 4 x 1.5V ‘AA’ batteries or AC adaptor (9V/1A)
Battery Life approx. 24 hours (alkaline batteries)
Dimensions / Weight 200 x 70 x 57mm / 190g
