Twenty-one workers were killed Wednesday in a methane-gas explosion in a Colombian mine. The mine had been the site of another fatal blast four years ago. The disaster occurred during the 7 a.m. shift change. While the manager of the mine declined to speculate on the cause, the Red Cross said methane-gas buildup was to blame. Methane-gas buildup had caused the 2007 explosion at the mine, in which 32 people were killed. Although the mine met safety requirements, the Ministry of Mining and Energy said Wednesday it would be shut down pending an investigation. Despite the mine being described by local residents as “deadly,” relatives of those killed said mining is the only source of employment.