Risk assessments are living documents that follow machinery from inception to decommission. This documentation and process helps owners implement and maintain a suitable and safe environment for their employees. It is important that risk assessments are not only thorough, but easy to create and follow. The process of designing and maintaining safety systems for automated equipment can be broken down into 5 simple steps.
- Identifying Hazards
- Assessing Initial Risk
- Risk Reduction
- Assessing Residual Risk
- Validating Solutions.
Step 1: Identifying Hazards
risk is calculated by using
the 3-2-3 rule to quantify hazards
from RIA TR R15.306.
Risk assessments can start out as technical lists created by machine designers prior to the equipment’s release to fabrication. A team of knowledgeable and qualified personnel should step through the process steps to identify all hazards that exist before safeguarding is implemented. They are not just considering operators; they are considering everyone who could be harmed from the hazard. For example, a UV cure light could pose risk to the immediate operator, but have the technicians who are walking by the equipment to lunch been considered? How about the maintenance personnel working on the equipment? It is important to consider all potential when conducting a risk assessment.
Step 2: Assessing Initial Risk
To understand the magnitude of risk for each hazard on the machine, the risk must be quantified. There are three qualities to quantify: Severity of Injury, Frequency of Exposure, and Probability of Avoidance. The 3-2-3 convention (Figure 1) may be used to calculate a risk value that represents the level of risk to personnel before safeguards are considered. This method is recognized in RIA TR R15.306 Table 2 as an accepted way to quantify risk.
Step 3: Risk Reduction
After all machine hazards have been appropriately identified and quantified, risk reduction measures should be taken. Not all risk reduction measures are made equal, however. The hierarchy of hazard mitigation, also called the hierarchy of controls, organizes mitigation principles by effectiveness. This cornerstone of risk reduction is seen in some capacity in both ISO 12100 and ANSI B11.0 standards.
Now consider a pinch point that exists between a moving pallet and weldment in the initial design. If the designer systematically moves through their design and catches the pinch point before the machine is released, they may choose to move the weldment back several inches, eliminating the hazard all together. Consider a second example: If laser marking is an operation of the machine, the operator may be given a hood that protects him from harm, but what is in place to ensure they are wearing it? What about bystanders? Instead, it is safer for the PLC (Programmable Logic Controller) to not allow the laser to begin marking until the safety doors have been shut (interlock switches have been met).
Step 4: Assessing Residual Risk
When all hazards have been recorded and the most effective risk reduction measures planned, they should be rated again to identify residual risk. All machines after safety controls have an element of “residual risk.” It is up to the risk assessors to determine if that residual risk is acceptable or not.
Step 5: Validate Solutions
After safety measures are in place, they must be proven effective. Recording proof or validating safety controls is the final step to completing a risk assessment. For example, the documentation of stop time measurements, ensuring light curtains are installed at the appropriate distance away from the closest hazard is validation. Maintaining certifications of light tight boxes is validation. It is not enough to implement safety controls: safety controls must be implemented correctly.
If completed with thought, genuine effort, Risk Assessments are a valuable tool that help designers and end-users create and maintain safe automation equipment.