The fire trucks are pulling in again at 36th and Lexington. It’s the second time in the past few years — once a couple of years back for a huge blaze that blew out windows and blackened the facade of the brownstone at 135 East 36th, and today for a partial collapse of the same building. The brownstone is home to the Namibian mission to the United Nations, and it sat, dark and burned-out at the end of its well-kept block, until earlier this year. Several months ago, the Namibians started a major renovation, one that called for the whole back of the building to be sawed off and a new glassed-in wing to be built over the rear garden. And we could not help noticing, once the scaffolding went up, that the walls had been secured — or “secured” — with huge angle irons bolted through the brickwork. We’ll be walking on the other side of Lex for awhile.