Safe-to-spend is about your current obligations, and other stuff that would reduce your "really available" balance; there's more money physically in the account, in a true emergency you'll rob from tomorrow to pay today's emergency room visit.

Of course, now you need a way to pay for tomorrow, but there's still options: skip a bill or two this month, borrow money (from friends, credit card, payday loan, sell your internal organs), work overtime, or whatever.