It turns out they sent an engine to New York with a dozen volunteers after the Chitauri invasion.
The Agents track the commonality behind the attacks to a fire station that both men had worked at. A souvenir from the Battle of New York–a Chitauri helmet–was the cause.
The production filmed at a real fire station, Long Beach Fire Station 14, located on Eliot Street in Long Beach. This location took a while to find. There are a lot of fire stations in the Los Angeles metro area. A big break came when enhancing an image below, I discovered the number 518 on the front of the firetruck. Taking a chance and googling Stations that have used engine 518, it turned up a short list of Long Beach stations. From there, it was a quick search of stations that had parks across from them and matched the general appearance seen in the episode.
MAP
(Agents of SHIELD S01E06, 2013)





