Window Guard Requirements Philadelphia

[Eric Seo]

Is anybody familiar with building code requirements relating to window guards/stops in small multifamily buildings in Philadelphia?  I just had an inspection for a duplex renovation in Philly and one of the items the inspector noted is that we need to put something in place to keep the second and third story windows from opening more than 6 inches.  

Wondering if anyone has experience with this and what was used to address the issue. Any insight would be greatly appreciated. Thanks!