where did you get this info? The legal safe limit set by osha is 10% or 10,000 PPM. The lethal amount for a human is 30% or 30,000 PPM.
Wow I almost don't know what to say about this...but I do
Lets start with some basics.....PPM stands for Parts Per Million. Now for some basic math 1,000,000 divided by 10,000 = 100 so according to YOUR math there is 100 10%'s ( or more simply 1000%) in 10,000 PPM.
The correct math for figuring percentages is to take the part/the whole x 100....i.e. 10,000/1,000,000x100=1 Simply put 10,000 PPM is 1%, therefore 30,000 would be..... you got it 3%!
2nd. any chemical or element you can think of has a MSDS (Material Safety Data Sheet) available online, if you look at CO2 MSDS you will find that concentrations of 30,000 PPM (3%) can be worked in without breathing apparatus for up to 15min at a time. Fresh air for a few minutes and you can go right back in. It also states that at 40,000 PPM (4%) it IS an IMMEDIATE risk to your health and well being.
So the real question is where do YOU get your information from? People need to quit posting chit they know little or nothing about and presenting it as fact. If you are guessing, admit it.
Used properly and safely CO2 will kill any insects you want it to cheaply and without harm to yourself or others.
Small plants- put them in a 55 gallon garbage bag, squeeze about 1/2 the air out, fill with CO2 until it bulges and tie it off tight, come back an hour later, vent out the CO2 and try and find a living thing on your plant. You will need to do this every couple days until you have passed the the full life cycle of the eggs of the species you are trying to kill. Bigger area take some plastic creativity, some good tape and a good ventilation plan.
Remember folks just cause you heard it on the internet doesn't make it true! Do your own research and make the most educated decision you can!
Good luck, good growing