Hazardous Gas or Chemical Definition / Resource?

I don't believe there is a specific definition in LEED. See the glossary entry below for some help. However certain items have always been considered relevant to this credit. Off the top of my head I can think of: cleaning supplies, car exhaust, large-volume printers, soiled utility rooms, labs, regulated chemicals. Anything that volatilizes and has a smell, pleasant or not, is a prime target; even if it a green chemical as in your case. When in doubt air it out. More specifically use source control liberally. Remember your objective is outstanding air quality.

hazardous material (from USGBC glossary)
any item or agent (biological, chemical, physical) that has the potential to cause harm to humans, animals, or the environment, either by itself or through interaction with other factors

On the particular "Green Cleaning" piece, we've had reviewers require hard lid ceiling and exhaust for janitors closets even if green cleaning is pursued. The logic given was that green cleaning policies set best practices but hazardous chemicals may still be used on occasion.

Refering to the question regarding hazardous gas or chemical definition, I would like to ask if trash rooms and rooms where oil or grease separators are located should be included in the requirements of appropriate exhaust (0.5 CFM/SF)? These rooms are located underground.

I would definitely apply the credit requirements to a trash room where there are undesirable smells, unless you can justify there is no exposure pathway to any building occupants