Cumbria Police say a substance, "believed to be noxious", is coming from the building in Ulverston.
A man remains inside a property amid an ongoing police operation.
Tributes were paid to service personnel at a special event held in their honour - Armed Forces Day 2026.
A tense police standoff in a residential street has come to a safe conclusion.
Crowds gathered in Carlisle city centre on Saturday to mark Armed Forces Day.
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