Bloomberg: Twitter’s new video streaming app, Periscope, launched on Thursday morning. By the afternoon it was facing its first real test as a medium for citizen journalism. Just after 3 p.m., a large explosion shook a building on Second Avenue in Manhattan. By the end of the day two buildings had collapsed. People who signed on to Periscope out of curiosity about Silicon Valley’s latest craze in self-documentation were given an intimate look at the confusing scene on the ground in the immediate aftermath of the explosion.