My last blog post was about machine safety with a focus on the different categories and performance levels of machine safety circuits. But I just briefly touched on how to determine these levels. By default, we could design all equipment with the highest-level category and performance levels of safety with an abundance of caution, but this approach could be extremely expensive and not the most efficient.
Enter the important concept of risk assessments which enable us to identify, evaluate, and prioritize potential hazards and risks associated with specific activities, processes, or systems. Whether it’s in the domain of occupational health and safety, environmental health, or product safety, risk assessments can guide us toward ensuring the safety of those who may interact with these hazards. This process involves the following well-defined series of steps, including hazard identification, risk analysis, risk evaluation, and risk control.
Hazard identification involves identifying potential hazards and risks associated with the activity, process, or system you’re assessing. This can be done using a variety of methods, such as observing the process, reviewing relevant documentation, or consulting with experts.
Looking at Figure 1, what are the hazards? They are pinch points from the robot, crush points from the robot, and shock or burn from the end effector. Another potential hazard that cannot be determined by the picture is the speed at which the pallet is traveling. Identifying the hazards is an important step because you cannot mitigate a risk without properly identifying it first.
Analyzing the likelihood and severity of the identified hazards and risks is key to risk analysis. Various methods, including the use of historical data, simulations, or mathematical models can facilitate this.
Risk evaluation involves assessing the significance of the identified hazards and risks by considering their exposure, severity of injury, and the likelihood of avoiding that hazard. In this example, the robot could potentially crush you, making it a high severity. When the robot operates at full speed, the likelihood of avoiding it is low. In the case of an automated cell, exposure may be infrequent, but maintenance on the robots will still be necessary.
Risk control encompasses the identification and implementation of measures to prevent or mitigate the identified hazards and risks. This can include redesigning the process, implementing safety controls, or providing training to employees.
Again, the category and performance levels of safety controls required are based on the defined risks.
In our robot example above, the first control we would implement is an enclosure around the robot to prevent people from getting close to the hazard. We cannot have an enclosure without some method for entering the enclosure, so we will add a door to the enclosure. It’s the door’s interaction with the cell that must have the appropriate category and performance level based on our evaluation. When the door is open, we will limit the operation and speed of the robot. We can use a teach pendant with a “dead man” switch that requires the person inside the cell to hold it while operating the robot at a slower speed. This will decrease the likelihood of a hazard. Additionally, we would need to have a method for the pallet to enter in and out of the enclosure.
Risk assessments should be conducted with a group of qualified people which may include safety personnel, engineers, managers, and potentially end users familiar with the automation process. The risk assessment process is iterative in that it may need repeating if new hazards or risks are identified, or if changes are made to the activity, process, or system being assessed.
Have a safe day!
Click to read my previous blog post Focusing on Machine Safety.