At the using location working enviroment OSHA dicates the air quality of the plant which I bellieve is currently 35 parts/million or ppm of CO. Air exhange system must be able to keep the level at or below this level. Forklifts (ICE) being a producer of CO can affect the concentration as well as other processes in a manufacturing enviroment. Keeping your forklift in good running condition would be good advise, especially if the one you buy has been qualified/certified to meet the EPA emission standards set at the time of manufactuer -ie Tier I, II, III etc.
Today most first line dealers have equipment to test exhasut emission & are knowledgeable of the emissions levels for the brand(s) they represetn & maybe knowledgeable of other brands too.
Most dealer service people are capable of working on other brand equipment, there maybe be 1 or 2 brands they prefer not to work on. Service people with experience have "learned" about competitve makes over teh years. And dealers love to work on msot makes as it does give them an opportunity to take business away from the other guys.