What is Safe?

We want our children to be safe at school.  We want a foot bridge to be safe when we cross.  We want food to be safe to eat.  And so much more.  What are we thinking?  Does safe mean without risk?  Major highways are designed to achieve a risk level of one in a million passes around the bend or over a hill. Is that safe enough?  It is well documented that people do not have an accurate understanding of risks associated with activities.  Chain saws are much more dangerous (likely to cause harm) than nuclear reactors, but feared less.  We don't communicate clearly about risk.  If you are playing musical chairs, and there are 99 chairs for 100 people, it is certain that one person will be left standing.  On the other hand, in a large field pocked with gopher holes,  100 buffalo run across. Perhaps, one, two, ten or none will trip and fall.  Which activity is riskier?  We protect pedestrian crossings to varying degrees of security.  Sometimes a cross walk, sometimes a crossing guard, sometimes a pedestrian overpass.  Is each method appropriate to the risk of being hit by a car?  Of course, all risk assessment is relative to the circumstances but all fear is not.  Our fear as individuals and our collective fear expressed in public policy and law is often not proportional to the actual exposure to harm.  I will have plenty of time to think about this soon when I take a flight to Philadelphia.  I'll have to wait in a long line just to take off my shoes.