Pizza Vents and other vents in NYC

Can anyone explain to me how venting works in regards to the health and fire department. I'm in NYC, and I saw a store that has what they call a "pizza vent" even though they are using gas ovens to bake their pizzas.  The way I understand it is that if you have an open flame, you need to have a type 1 venting system.  So how come these guys just have a vent that goes from the oven to the outside?  They don't have a hood or ansel system.  I'm trying to open a concept similar to pizza in that it is a baked flatbread, but in my location search venting seems to be the biggest factor and I don't know how to find out what exactly I need.  Can someone answer this or point me in the right direction?

Thanks!