If their standard for shutting it down is “exceeds background” (which is probably more about Uranium glass than deck markers) than they will have to shutdown the grocery store (Bananas are radioactive as they contain Potassium 40, so yes standing near them will “exceed background”), and your kitchen if you have a granite countertop (contains traces of Uranium 238), and your house if you have smoke detectors (Americium), oh and if you have an old radium dial wrist watch I guess they have to cut your hand off now?