Above 2%, carbon dioxide may cause a feeling of heaviness in the chest and/or more frequent and deeper respirations.
Toxic levels of carbon dioxide: at levels above 5%, concentration CO2 is directly toxic. [At lower levels we may be seeing effects of a reduction in the relative amount of oxygen rather than direct toxicity of CO2.]
At normal oxygen level, 7% co2 concentration can be lethal, and the OSHA standard for lethal dosage is 10% concentration within 30 minutes.
At lower oxygen level the effect of co2 poisoning is much stronger on human body.
5lb co2 in a 12'X12'x9' room is 5.15%
air density is 0.075lb per square feet at 70 degree, in a room of 12'x12'x9', is 97.2lb.
97.2lb(air)-5lb(air been pushed out)+5lb(co2 from 5lb co2 tank)=97.2lb(mixed air)
over the toxic level
In a smaller room the concentration is higher.
Recently a lot of fellow members build their own co2 pressurized system, while building or after the system is built, CO2 safety is really important and must be kept in mind. AND MAKE SURE YOUR CO2 SYSTEM IS 100% FUNCTIONAL AND HAS NO LEAK.
Personally, it only take less than 2 hours to build a system if all parts are ready, but takes up to two weeks for a different series steps of test to make sure the unit is 100% functional and no leak.
And I keep the house windows open when playing with new systems.
Hope you do the same if you are building a co2 system.