a Tunnel Critical Velocity calculation program employs the most commonly used model developed by Kennedy et al. to determine the ciritcal air velocity in tunnel ventilation for smoke control. To calculate critical velocity in tunnel, a CriticalVel program solves a coupled set of equations by iteration. Highlights: calculates critical air velocities in tunnel ventilation for smoke control as per NFPA 502. built-in customized area calculator. Options available are Partial circle, Segment circle, Half circle + rectangle, Half ellipse + rectangle, and Rectangle. built-in air density & air specific heat calculator. "save-to-file" function with built-in text file viewer. in SI-IP Units. for details, see http://pocketengineer2. sharepoint.com/Pages/aCriticalVel. aspx.