Friday, February 15, 2013


A news report out of Russia tells of nearly one thousand people being injured this morning when a meteor exploded overhead. The meteor was said to weigh some 10 tons and was traveling at 30,000 to 40,000 mph when it entered the atmosphere and broke up. Fragments left holes measuring 15 to 20 feet across in the ice over a lake.

The injuries and property damage from this meteor are sad, indeed, and the victims warrant our concern. The event, however, should not cause the rest of us to live in fear of death from the sky. Understanding the actual hazard from such events is the business of the field of risk assessment. Adler's book, above, was the first thing I had read on the subject. The earliest copyright date I've found is 1973, but my sense is I read it even earlier. Maybe not. Its subtitle, Death from Falling Watermelons, succinctly summarizes the essence of risk. The diagram below explains:

Risk is the product of the likelihood of an event's happening and the consequences of the event if it does happen. If an event is certain and it can be expected to lead to death, then the risk is clearly very high. Think "if you walk into that room you will be shot multiple times." A non-suicidal person would likely not walk into the room. Conversely, if an event is highly unlikely but the consequences if it does happen are minor, then we have no reason to be concerned. You get the point.

We  never walk down a street scanning nearby rooftops for watermelons because it simply doesn't happen. Yes, if one did fall on our head it would really ruin our day, but the risk is so low that it doesn't occur to us to be concerned. But there is a difference between perceived risk and actual risk. Sometimes we grow so accustomed to an action that carries significant risk that our perception of that risk is numbed. Consider riding in an automobile and not using the seat belts. Consider continuing to burn fossil fuels despite the evidence of global warming and it's impacts. Sometimes our perceptions of risk are heightened by the newness of a technology. Consider choosing coal over nuclear for electricity generation, when the cumulative impacts of coal are much greater than the nuclear fuel cycle. I once saw a cartoon of a bumper sticker on a coal truck that proclaimed, "There's no fuel like an old fuel."

Every action we take has risks, even breathing, and we all unconsciously do risk assessments on a continuing basis. But are we dealing with actual risk or simply perceived risk?


  1. Good points, Jim. Sometimes the risk we've always taken seems less risky than the unknown -- even though it's not.

  2. Reminds me of this: Got a problem?.... Can you do something about it? = Yes - then don't worry. = No - then don't worry.

  3. There's an entertaining chapter in Bill Bryson's book "Notes From A Big Country" about the "Statistical Index For The United States" which reveals that every year 400,000 Americans are injured as a result of their bedding, 50,000 are injured each year by pens, pencils and other desk accessories, 400,000 by chairs, sofas and sofa beds and 142,000 by their clothing - (I got mine caught in a zip-fly when I was a little boy but since that dreadful day I've escaped unscathed!). It all makes falling meteors seem pretty harmless. Be careful when you turn in for the night, Jim!