A spark from a welder’s torch ignited a fire that caused $1 million in damage to a warehouse on the grounds of the US Coast Guard Base in Boston’s North End on Tuesday, the Boston Fire Department said. On its official Twitter account, the department said the fire struck a three-story building on the Coast Guard base on Commercial Street at about 9:30 a.m. The fire was quickly brought under control, and no injuries were reported. A new vent system was being installed, and welders were working on the roof when an “inadvertent spark cause[d] some combustibles to catch fire,’’ the Fire Department reported.John R. Ellement can be reached at email@example.com. Follow him on Twitter @JREbosglobe.