The Oxford English Dictionary (Oxford University Press, 1971) defines risk as a "hazard, danger; exposure to mischance or peril". Therefore, to put oneself "at risk" means to participate voluntarily or involuntarily in an activity or event that could lead to injury, damage, or loss.
Voluntary risks are hazards associated with activities that we decide to undertake (e.g., driving a car, riding a motorcycle, climbing a ladder, smoking cigarettes, skydiving, formula one racing).
Involuntary risks are negative impacts associated with an occurrence that happens to us without our prior consent or knowledge. Acts of nature, such as being struck by lightning, fires, floods, tornados, etc., and exposure to environmental contaminants are examples of involuntary risks.
Risks may also be defined as statistically verifiable or statistically nonverifiable. Statistically verifiable risks are risks for voluntary or involuntary activities that have been determined from direct observation. These risks can be compared to each other. Statistically nonverifiable risks are risks from involuntary activities that are based on limited data sets and mathematical equations. For example, we know the risk of a meteorite hitting a person is low, but because there is no record of such an event ever happening it is statistically nonverifiable. Statistically verifiable and nonverifiable risks are similar to apples and oranges in that they are both fruits but are so different that comparisons should not be made between the two.
Risks associated with different activities and phenomena vary greatly. For example, as the Riskometer illustrates, the chance of getting struck by lightning in the United States is low compared to fatality due to fire. These are involuntary risks, those that we have little control over.
Voluntary risks, on the other hand, are associated with activities that are largely controllable. Risk is a part of living; consequently, we are constantly evaluating the risks that face us on a daily basis. You may not be conscious of this assessment, as it is often ingrained in our thought processes; however, you are considering risks, especially as they relate to voluntary activities, to ensure that you and those close to you are out of harm's way. For example, when leaving the house in the morning, you may consider if there is a chance of rain. The risk of getting soaked on the way to work is a risk you could avoid by carrying an umbrella.
Of course, there are many common activities that present more serious potentially life threatening risks. Transportation may be one of the most serious voluntary risks that we take on a regular basis. Driving a car or a motorcycle has a relatively high risk of injury due to accidents.
Many of us may depend on driving a car to get to work or other destinations; therefore, we are willing to take the risk in order to support our families and for the convenience it provides. To reduce the risk of accident and injury, safe guards such as air bags and antilock brakes are standard features on most vehicles. In addition, we can take risk precautions, such as reducing speed, increasing following distance in poor driving conditions, and wearing seat belts.
Risks to the public are measured by direct observation or by applying mathematical models and a series of assumptions to animal risk study results to infer potential risk to humans.
No matter how risks are defined or quantified, they are usually expressed as a probability of effects associated with a particular activity. Risk/probability is expressed as a fraction, without units, from 0 to 1.0. A probability of 1.0 indicates an absolute certainty that an event or outcome will occur. Scientific notation is generally used to present quantitative risk information.
|Actual Number||Scientific Notation||Read As|
|1/10||1x10-1||1E-01||One in ten|
|1/100||1x10-2||1E-02||One in a hundred|
|1/1,000||1x10-3||1E-03||One in a thousand|
|1/10,000||1x10-4||1E-04||One in ten thousand|
|1/100,000||1x10-5||1E-05||One in a hundred thousand|
|1/1,000,000||1x10-6||1E-06||One in a million|
|1/10,000,000||1x10-7||1E-07||One in ten million|
A risk assessment is typically performed in four steps: