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ARET - A machinery risk assessment tool


Health and safety of the work environment is an increasing concern for everyone. For example in 2009, the U.S. Bureau of Labor Statistics reports 734 fatalities involving contact with objects or equipment and 3.9 cases per 100 full-time workers of nonfatal injuries where 31% of cases include lost workdays. Through a risk estimation of our equipments we can identify our major risk equipment and then address the problem with a risk reduction analysis.

The ARET tool, which stands for Average Risk Estimation Tool, computes the average risk level of many risk estimation tools. The tool is built around the equivalency scales developped in a Master Thesis (Florence Moulet, UQTR, 2010) which permits to compare different risk estimation tools. Mostly the tools evaluated follow the 2 configurations proposed in ISO14121-1:2007. The first configuration method has 2 parameters, severity (S) and probability of harm (Ph) and 20 tools are evaluated in ARET2. The second configuration has 4 parameters; severity (S), probability of event (Pe), avoidance (A) and exposure (Ex) and 6 tools are converted. The risk level are converted to a 0 to 100% risk level scale. The ARET tools, described later, compute an average of the equivalent risk level of the underlying tools.

Parameter scales

  • Severity (S)

    Severity represent the extent of the possible injury due to a hazardous event. It has the following 8 levels:

    1No injury
    2Minor injury, first aid only, reversible
    3Injury requiring medical attention, reversible
    4Injury requiring medical attention, irreversible, able to return to work
    5Injury requiring medical attention, irreversible, difficult to return to work
    6Major injury, unable to return to work
    8Multiple deaths

  • Probability of harm (Ph)

    The probability of harm represents the likelihood that a hazardous event will result in the severity defined previuosly. It has the following 7 levels:

    1Rare, almost impossible
    2Very unlikely
    6Very likely
    7Almost certain

  • Probability of a hazardous event (Pe)

    The probability of occurrence of a hazardous event defines the frequency that a hazardous event may occur and has 5 levels as shown in the next table.

    1Rare, almost impossible
    5Almost certain

  • Avoidance (A)

    Avoidance refers to the possibility of a trained worker to escape from a hazardous event. 6 levels are defined for A.

    1Almost certain
    5Rarely/Very difficult

  • Exposure (Ex)

    Exposure can be subdivided in 2 types : frequency and duration. The ARET4 tool is based on the exposure frequency for which 8 levels are defined in the next table.

    1Less than once per year
    5Once a day
    6Many times a day
    8Continuous exposure or many times a day for long period of time

    Risk levels

    The risk level for the ARET tools are measure between 1 and 100%. Then the risk level is compared to 4 categories of action that may be required. The 4 categories are:

    1GreenThe estimated risk level is low.
    You don't need to do a risk reduction analysis.
    2Light greenThe estimated risk level is tolerable.
    You can do a risk reduction analysis to further reduce the risk.
    3YellowThe estimated risk level is high.
    You should do a risk reduction analysis and take actions to reduce the risk at a tolerable level.
    4RedThe estimated risk level is too high.
    You need to do a risk reduction analysis to mitigate that risk and make the necessary changes to reduce the risk to a tolerable level.

    Tools description

    This is a 2 parameters tool for estimating a hazardous situation for a machine. It uses parameters S and Ph to compute the average risk level of 18 different tools.

    This is a 4 parameters tool for estimating a hazardous situation for a machine. It uses parameters S, Pe, A and Ex to compute the average risk level of 3 different tools.

    How-to use the tools

    Simply click the tool you want to use. Then evaluate each parameter for the hazardous situation under consideration and press compute to view the evaluation of the risk. The next part will be to take action based on the risk estimation. Unfortunately, for this part we don't have a tool yet to assist you.


    Anyhow, no tools are perfect, some tend to underestimate while others overestimate the risk. The main advantage of the ARET tool is that it presents an aggregate value of many tools in just one click. The final decision is in your hands and no tool can replace the judgement and experience of a person.


  • ISO14121-1:2007 Safety of machinery - Risk assessment - Part 1: Principles
  • Moulet, Florence (2010). Étude comparative des outils d'estimation des risques associés aux machines industrielles, Master Thesis, Universite du Quebec a Trois-Rivieres
  • U.S. Bureau of Labor Statistics - Injuries, Illnesses, and Fatalities