In 2011 a powerful tornado tore through Joplin, Missouri, killing 158 people and injuring more than 1,000. Many of the casualties were people sheltering in big box stores that were effortlessly ripped open by the funnel's more than 200-mile-per-hour (321 kilometer-per-hour) winds, leaving collapsed roofs, crumbling walls and scattered inventory in their wake [source: NOAA]. While this particular tornado was exceptionally strong, it turns out that most big box stores aren't even designed to handle a storm half that potent.
Architects design big box stores to be built quickly and cheaply, and those in Joplin were no exception. Constructed of cast concrete or concrete block walls and topped with relatively lightweight roofs, these simple structures met city code, but that only guaranteed they could withstand 90-mile-per-hour (145 kilometer-per-hour) winds [source: Murphy]. Unfortunately for those hunkered down in the big box stores, their shelter didn't stand a chance.
If you do find yourself stuck in a big box store with a tornado approaching, there are some things you can do to keep yourself as safe as possible. Your best bet is to head for a safe room if the store has one. These are reinforced rooms where customers can shelter in case of severe weather. Otherwise, look for restrooms, closets or other smaller rooms that might offer protection from falling roof debris. Just remember to stay away from tall shelves — you don't want them or their contents to land on top of you [source: FEMA].