Hi,

I recommend the book Gardening Indoors with CO2 by George F. Van Patten, Allysa F. Bust andTom LaSpina. ISBN 1-878823-19-1. A small book less than 100 pages, it covers the basics to help you get started.

Ambient levels of CO2 are approximately 350 ppm. Some plants are more sensitive than others, but generally you can have up to 1500 ppm in a growing space before you hit diminishing returns in plant growth.

Safety requirements depend on the method of CO2 injection you plan to use. From what I have read, OSHA specifies an eight hour weighted time average of 5,000 PPM, while short term exposure of fifteen minutes not exceeding 30,000 ppm. An excess of carbon dioxide is harmful to plants also, in addition to being a waste of money, so controlling injection into the grow space is pretty important. Commercial growers would probably use a Nondispersive Infared sensor to constantly monitor co2 levels, in additon to to controlling the timing of injection to be coordinated with air ventilation and circulation.

Assuming you will be burning some type of petroleum in a CO2 generator as a way of adding CO2, you would also need to monitor, or at least be aware of the possibility that particular pollutants such as carbon monoxide, sulfur dioxide, leaking petroleum or other pollutants could be present and would be harmful for both humans and plants. This can be addressed with proper  maintenance, choice of fuels, activated charcoal filters or additional sensors.

Hope that helps!

This is an application where engine generator exhaust is to purified and a portion  introduced into the greenhouse to elevate CO2 levels.  The generator is to be fueled with a wood gasifier.