I’m having difficulty finding the Hazardous Materials Classification chart for H2CO3. I mean the graphic with the 4 diamonds forming a larger diamond, like this.
It’s 0-0-0-0, about as perfectly safe as you can get. Even California doesn’t consider it hazardous.
For what it’s worth, I Googled “Materials safety data sheet H2CO3”.
Chronos has posted the MSDS for <1% Carbonic Acid. It’s important to know the pressure and concentration to give you a good answer.
CO2 is also known as Carbonic acid gas and Carbonic anhydride - see here ICSC 0021 - CARBON DIOXIDE
Also here is the NFPA 704 sign for CO2 - NFPA 704 Sign for CO2 | CO2Meter.com
The chemical formula you posted is for carbonic acid, which is a very weak acid that forms in small amounts when CO2 is dissolved in water and is practically harmless. I’m having trouble thinking of a reason you would need to post a hazardous material classification for it. Is there some larger task at hand?
ETA: Are you maybe thinking of carbolic acid (phenol)?