Accidental occupational exposure  in coal miners  and grain containers is the commenst methods of toxicity

Others involve accidental toxicity in anaethesia when an oxygen cylinder becoming emptywhile co2 cylinder is still functioning

Clinical picture:

1- 3% CO2 in atmosphere cause headache, drowsness , and loss of muscle power.

 2- With high concentration death is rapid with no asphyxial signs mainly due to vasovagal reflex causing cardiac arrest.

3- Minimal fatal concentrations of CO2 in blood is 60-80%.