Do you agree it has to be listed for fire protection use??Insurance Engineer said:If hydraulicly it can be proven it will work you can do it as per NFPA 24 and 13. BUT most likely not, the flow will be about 150 GPM .10/1500 or less if they use quick response sprinkler. What is the static and residual city water pressure, how many feet of 2" main do we have from the building to the city street, do we have any elevation change between the two points. Is it a straight run or do we have many elbows. How old is the pipe if old most likely not 2" anymore because of interior corrosion, what type of pipe copper, steel, cast iron. As you can see many factors to be considered. Make sure you get a sprinkler contractor involved and review the hydraulics calculations line by line that will be the only way to know for sure. If it works you are good, if not we'll nice try, now put in a new properly sized main.
If so have you seen two inch listed for fire protection use?