Step 1 – Risk assessmentFood to be packaged is loaded into the cell manually through the rear door. A batch is prepared for the packing conveyor in the infeed hopper. The cell is reset and restart-ed. The packaging machine with conveyor belt only oper-ates when both doors are closed and when the protection system has been reset.In the risk assessment it was established that the machine is to be operated in three shifts (8 hours per shift) 365 days a year. The total access to the danger zone is estimated to be four times per hour (F2), including manual packaging and tending operational disturbances. Unexpected start-ups are not considered to cause serious injury but rather minor heal-able injuries (S1). The operator is considered not to have the possibility of avoiding injury as the machine moves quickly (P2). The number of cycles for the safety function = 365 days/year x (3x8) hours/day x 2 cycles/hour = 17,520 cycles/yearThe assessment for the safety function required for access to the machine is PLr= c (S1, F2, P2). In addition to this safety function, an emergency stop function is needed. This is also assessed as PLr=c.Determination of the PLr necessary for the safety function with interlocked door for this example.NOTE! The assessment needs to be made for each safety function.Key switch MKey5Monitors that the door is closed.Safety relay SentryMonitors safety compo-nents.Emergency stop buttonTo stop the machine in case of danger.Step 2 – Reduce the riskAs protection, an interlocked door is selected with the key switch MKey5. Stopping time is short enough for the dan-gerous movement to have ceased before the operator can access it. The emergency stop is placed within easy reach, on both sides of the cell near the doors. —Case study 1 - Safety relay SentryProtection layout for a packaging machine with low risksabcdePLrP1P2P1P2P1P2P1P2F1F2F1F2S1S2low riskhigh risk11– 16SAFETY PRODUCTS CATALOG ABB JOKAB SAFETY
