A postal worker with burns on her hands who touched white powder from a letter went to Des Moines’ Mercy Hospital about five o’clock this morning, scrambling a haz-mat crew and forcing the emergency room to be sealed off. Hospital spokeswoman Daphne Christensen says the whole medical center was sealed off. Christensen says the facility had to be locked down because a second postal worker arrived and used another entrance so everything was sealed off to ensure no contaminants were spread. Officials now say the substance was rat poison mixed with flour. Both postal workers were treated and released. The ER is open now. An investigation of the letter is underway.