WASHINGTON — Engineers scheduled to begin rappelling down the Washington Monument today experienced unexpected delays when they had to construct a barrier around the monument’s lightning rod system, and the possibility of thunderstorms threatened to push their daredevil visual inspection back further.

The monument was damaged last month by a 5.8-magnitude earthquake that shook the nation’s capital, and the site has been closed to visitors ever since. Engineers from a private firm retained by the National Park Service have spent the past month inspecting the interior of the 555-foot obelisk, where pieces of stone and other debris rained down during the quake.

Now, a “difficult access team” from engineering firm Wiss, Janney, Elstner Associates is looking for additional cracks and chips on the exterior of the structure, and rappelling will afford them the best up-close look.