Treat it like air which is about 80% nitrogen.  

My first stop would be "Industrial Ventilation: A Manual of Recommended Practice for Design" published by the ACGIH

Compressed Gas Association has standards but they are relatively expensive and may be too specialized for nitrogen and just taking away low pressure (near ambient) vapor, if that is what you are doing.  I agree with chicopee and redgdon:  nitrogen is pretty much air, and ACGIH Industrial Ventilation is the bible on ventilation design.  Get the MSDS's for liquid and gaseous nitrogen as a starting point.  You need to know your vent flow character and discharge path configuration, etc.  If you are looking at whole system instead of only low pressure gas (ambient pressure) then release device, discharge piping, etc. need looked at.  Gas expansion and sonic choking in pipe may come in to play.  Simple to not so simple. If from a relief valve, get the Crosby handbook from Tyco/Anderson-Greenwood-Crosby http://andersongreenwood.com/literature.asp  (yeah, Tyco owns them, too).  Liquid nitrogen under pressure releasing and vaporizing to atmosphere involves more than just taking away vapor at typical air density. Hope this helps.