1.250-300ppm: The usual level of outdoor air

2.350-1000ppm: Common indoor air.

3.1000-2000ppm: May cause drowsiness. 

4.2000-5000ppm: Stagnant, stale and stuffy air levels. 

5.>5000ppm: Severe hypoxia. Danger level.

Specifications

Large LCD Display?3.5" (8.9cm)LCD display with backlight
Logger mode?key start/stop,lmmediately,Schedule,Real-time&Roll-over
Carbon Dioxide(CO2)
Range?0~9999ppm 
Accuracy?±70ppm/3% of reading(400~2000ppm) 
Response time?10s

Temperature 
Range?-10~70?(14~158?) 
Resolution?0.1?/? 
Accuracy?±0.6?/±0.9?(0~50?/32~122?),others ±1.2?
Humidity

Range?0.1~99.9%RH 
Resolution?0.1% 
Accuracy?±3%(10~90%) others ±4.5? 
Logging Memory?12700
Operating Condition ?0~50?,0~95%RH 
Storage Condition ?-20~60?,0~99%RH 
Sensor life?15years in normal comm Environments with ABC on 
Storage temp ?40~70?(40~  158?) 
Battery?4×AA type Alkaline Battery or USB -Power