Risk, Safety, Introduction to Risk Assessment.

Learning Goals: Introduce the general concepts of risk assessment. Differentiate it from risk management. Give some examples of risk assessments.


Risk assessments are required for many purposes, including regulatory compliance. We'll look at these in later modules. Here we just want to define some terms that we want to use correctly in risk analysis, but are often used carelessly in everyday speech.

Risk is just a statement of the probability and severity of some harm.

  1. "If you go snowboarding, you will probably break a bone." Is this a statement of risk?


  2. Well, what does it say about the "probability?"


  3. How about the "severity"?


    OK, here is a scientific statement of risk: "About 1 out of 750 unprotected workers with high exposure to vinyl chloride develop angioscarcoma (a rare liver cancer)." Although I was not very specific about what I meant by "unprotected" and "high," it states the probability and severity of a harm. (I guessed at the 750, the rest is true.)

    The word hazard is a very general term meaning some unsafe or dangerous, situation or thing. We use the term "hazard" and its adjective "hazardous" frequently, but neither are precise and should be avoided in technical descriptions of "risk."

    How about skydiving. Let's say the chances of being hurt while skydiving are: one minor injury per 500 jumps and one serious injury or death per 10,000 jumps. Is this a statement of risk? . Before you click on the little buttons with the "?" you should try to formulate an answer to the question.. (I made up those numbers too, but let's assume they are true.) Now would you describe skydiving as "safe?" Here we may not agree. Thousands of skydivers pay lots of money to jump out of airplanes. They admit there is a chance of them getting hurt, but enjoy the exhilaration of falling thousands of feet, and feel the risk is well worth it. They describe the sport as "safe." Do you? (I don't.)

    Think about it. We agree on the risks of skydiving, but do not agree if it is "safe." That is often the case. Why? The definition of "safe" is,

    Absence of unacceptable risks.

    (Or its equivalent, the presence of only acceptable risks. You can restate that defining "unsafe" similarly.)

    So now, when you read or hear that something is "safe," you should immediately ask yourself    . Again, safe and unsafe are words we often use, but they are very subjective.

    While we are defining, let us contrast the words "injury" and "disease."

    An injury usually occurs at a definite time and place. Most injuries are caused by a sudden release of energy. There is a clear cause and effect. A worker falls down and breaks her arm. The fall happened at a particular time and place. The fall is a transfer of potential energy, the height of the body's center of mass over the ground, into kinetic energy of the falling body.

    A disease is ill health. The time a disease is acquired is often vague. Many diseases have periods of incubation or latency. There is often a lack of clear cause and effect.

    In the field of industrial health and safety, safety is the prevention of injuries and industrial hygiene is the prevention of (workplace caused) disease.

    So the term "industrial hazard" might include threats of injury and/or disease. For example: gasoline is both a safety hazard (fire) and a health hazard (narcosis, skin irritation, and perhaps cancer).

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