Air Duct Broken
While not as sturdy as solid concrete, iron constructions have high structural integrity, requiring fewer support pillars.
Harvest drops
Iron× 10
Taken apart with a harvesting tool (axe, pickaxe, shovel), before perks and tool bonuses.
When it collapses
Falling, it leaves 
Scrap Metal Pile (60% of the time) where it lands.
Where to find (22 POIs)
Don Vittorio Spagetto Residence (tier 4), Downtown Marketplace (tier 4), Flushing Rule Palace (tier 4), Hotel Zombona (tier 4), HSP Logistics (tier 4), Pete's Outlet (tier 4), Super Shamway (tier 4), Town Hall (tier 4), Wasted Stiff's (tier 4), Jack's Lumber Mill (tier 3), Post Office #2 (tier 3), Savage Country (tier 3), Super Savage Country (tier 3), Aldos Cabinet (tier 2), Crack-A-Book (tier 2), Mo Power Electronics (tier 2), The Erickson Residence (tier 2), Pass-N-Gas Store #04 (tier 1), Box Factory, MeltDowns, Nav Pest Control, Wasted Mo Power.
Points of interest built with this block (any of its variants), the highest tiers first, from the game's prefab files.