Transformer explosion briefly blocks District intersection The explosion of an underground transformer briefly blocked a major intersection in the District's downtown Sunday afternoon, but did not cause any injuries or power outages, according to fire officials. Pepco spokeswoman Myra Oppel said the explosion at the corner of 19th and M Streets released a non-toxic mineral oil that brought a hazmat team to the scene. Fire officials checked one passerby who may have been exposed to the oil and said he was unharmed.