ARET - A machinery risk assessment tool
Background
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 represent the extent of the possible injury due to a hazardous event. It has the following 8 levels:
| Level | Description |
|---|---|
| 1 | No injury |
| 2 | Minor injury, first aid only, reversible |
| 3 | Injury requiring medical attention, reversible |
| 4 | Injury requiring medical attention, irreversible, able to return to work |
| 5 | Injury requiring medical attention, irreversible, difficult to return to work |
| 6 | Major injury, unable to return to work |
| 7 | Death |
| 8 | Multiple deaths |
The probability of harm represents the likelihood that a hazardous event will result in the severity defined previuosly. It has the following 7 levels:
| Level | Description |
|---|---|
| 1 | Rare, almost impossible |
| 2 | Very unlikely |
| 3 | Unlikely |
| 4 | Probable |
| 5 | Likely |
| 6 | Very likely |
| 7 | Almost certain |
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.
| Level | Description |
|---|---|
| 1 | Rare, almost impossible |
| 2 | Unlikely |
| 3 | Possible |
| 4 | Likely |
| 5 | Almost certain |
Avoidance refers to the possibility of a trained worker to escape from a hazardous event. 6 levels are defined for A.
| Level | Description |
|---|---|
| 1 | Almost certain |
| 2 | Likely |
| 3 | Possible |
| 4 | Difficult |
| 5 | Rarely/Very difficult |
| 6 | Impossible |
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.
| Level | Description |
|---|---|
| 1 | Less than once per year |
| 2 | Yearly |
| 3 | Monthly |
| 4 | Weekly |
| 5 | Once a day |
| 6 | Many times a day |
| 7 | Hourly |
| 8 | Continuous 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:
| Level | Color | Description |
|---|---|---|
| 1 | Green | The estimated risk level is low. You don't need to do a risk reduction analysis. |
| 2 | Light green | The estimated risk level is tolerable. You can do a risk reduction analysis to further reduce the risk. |
| 3 | Yellow | The estimated risk level is high. You should do a risk reduction analysis and take actions to reduce the risk at a tolerable level. |
| 4 | Red | The 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
ARET2
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.
ARET4
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.
Conclusion
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.