The schematic Jerry puts on the big screen is an electrical one. It is quite an assumption to make that it is for a ventilation system. There are no ducts showing on the plan.
When they are transporting the guy exposed to chlorine has from the van, the paramedic in the rear is wearing full hazmat ensemble. The driver is not wearing any protective gear despite the van being fully exposed to the rear compartment.
When entering an office building that was the target of a chlorine gas attack, Steve and other police officers do not wear any protective clothing or breathing masks.
Knowing that the gas was being released through the ventilation shafts, entering the building without taking any precautions could have fatal consequences as they take time to search every floor for the perpetrators.