Rescue crews were working to save two people clinging to scaffolding that was left dangling precariously on the side of a Baltimore high-rise after an explosion on Wednesday morning. The local Baltimore Firefighters Union said around 9 a.m. ET that an explosion on the 16th floor left the two workers trapped on scaffolding and crews were en route to rescue them. Another two people were being treated on the ground with burns. An hour later, the Baltimore City Fire Department said at least 10 people had been transported to area hospitals following the explosion and “partial roof collapse.” Nine were in critical condition, one was in serious condition. Work was being done on the building’s air handler and boiler system which likely caused the explosion, Fox Baltimore reported.