What is the test for a firefighter to enter a warehouse that they believe is on fire?

Under these circumstances, the firefighters had an objectively reasonable basis for believing that there was a fire inside the warehouse. Nothing in the Fourth Amendment required them to wait until they saw actual smoke or flames to enter a building that they reasonably believed might be on fire. Cf. Brigham City v. Stuart, 547 U.S. 398, 406, 126 S.Ct. 1943, 164 L.Ed.2d 650 (2006) (holding that the Fourth Amendment does not require police "to wait until another blow render[s] someone `unconscious' or `semi-conscious' or worse before entering").