Risk assessment and risk minimisationAccording to the Machinery Directive, the machine builder (anyone who builds or modifies a machine) is required to perform a risk assessment for the machine design and also include an assessment of all the work operations that need to be performed. EN ISO 12100 stipulates the requirements for a risk assessment. It is this that EN ISO 13849-1 is based on, and a completed risk assessment is a prerequisite for being able to work with the standard.Step 1 – Risk assessmentA risk assessment begins with determining the scope of the machine. This includes the space that the machine and its operators need for all of its intended applications, and all operational stages throughout the machine’s life cycle.All risk sources must then be identified for all work opera-tions throughout the machine’s life cycle.A risk estimation is made for each risk source, i.e. indication of the degree of risk. According to EN ISO 13849-1 the risk is estimated using three factors: injury severity (S), frequency of exposure to the hazard (F) and the possibility you have of avoiding or limiting the injury (P). For each factor two options are given. Where the boundary between the two op-tions lies is not specified in the standard, but the following are common interpretations and our recommendations:S1 bruises, abrasions, puncture wounds and minor crushing injuriesS2 skeletal injuries, amputations and deathF1 less frequent than once per 15 min*F2 once per 15 min or exposure time exceeding 1/20 of the overall operating timeP1 slow machine movements, plenty of space, low powerP2 quick machine movements, crowded, high power* We often recommend to choose a higher value to be on the safe side, e.g. once per day.By selecting S, F and P for the risk, you will get the PLr that is necessary for the risk source.Finally, the risk assessment includes a risk evaluation where you determine if the risk needs to be reduced or if sufficient safety is ensured.Risk estimationTo calculate the performance level required (PLr).S Severity of injuryS1 slight (normally reversible injury)S2 serious (normally irreversible injury or death)F Frequency and/or exposure to hazardF1 seldom to less often and/or exposure time is shortF2 frequent to continuous and/or exposure time is longP Possibility of avoiding hazard or limiting harmP1 possible under specific conditionsP2 scarcely possibleStep 3 - Design and calculate the safety functionsTo begin with you need to identify the safety functions on the machine. (Examples of safety functions are emergency stop and monitoring of gate.)For each safety function, a PLr should be established (which has often already been made in the risk assessment). The solution for the safety function is then designed and imple-mented. Once the design is complete, you can calculate the PL the safety function achieves. Check that the calculated PL is at least as high as PLr and then validate the system as per the validation plan. The validation checks that the specification of the system is carried out correctly and that the design complies with the specification.You will also need to verify that the requirements that are not included in the calculation of the PL are satisfied, that is, ensure that the software is properly developed and validated, and that you have taken adequate steps to protect the technical solution from systematic errors.Step 2 – Reduce the riskIf you determine that risk reduction is required, you must comply with the priority in the Machinery Directive in the selection of measures: 1. Avoid the risk already at the design stage. (E.g. reduce power, avoid interference in the danger zone.)2. Use protection and/or safety devices. (E.g. fences, light grids or control devices.)3. Provide information about how the machine can be used safely. (E.g. in manuals and on signs.)If risk reduction is performed using safety devices, the control system that monitors these needs to be designed as specified in EN ISO 13849-1.abcdePLrP1P2P1P2P1P2P1P2F1F2F1F2S1S2low riskhigh risk1INTRODUCTION1– 13
