Lafarge Tarmac turns to Siemens for auto crane safety validation 22 April 2014

Lafarge Tarmac's Tunstead cement plant has recently been modernised to provide safe access for maintenance around two automatic cranes used to handle raw materials, such as aggregates.

PLC programming, including distributed safety functions, was handled by Lafarge's in-house team, but Siemens Industry provided assistance with safety software validation.

Siemens' Howard Stott explains that risk assessments were undertaken to ensure compliance with all safety standards, with independent sign-off in accordance with the Machinery Directive 2006/42/EC Technical File Documentation.

"Our initial discussions highlighted the fact that Tunstead engineers were using the HRN [Hazard Rating Number] scoring method for risk assessment and risk reduction," explains Stott.

"A recommended way of determining the SIL [safety integrity level] and PL [performance level] levels is by tasking layers of personnel to undertake the assessment," he continues.

Multiple views are then recorded and the results combined for the best overall level of safety performance.

To provide the additional level of increased scrutiny and to support in-house system designers, the Siemens Safety team was contacted to perform a further assessment of the software both in terms of its structure and to ensure it reflected the recommendations, as published in manuals from Siemens.

"This type of external validation provides a clear and independent view of the software as recommended by the appropriate safety standards, as the more dangerous the machine or process the higher level of independent validation is required," states Stott.

"Assessment work of this kind can be performed off site as well as at the location, but the critical element is the independence of the competent assessor – in this case a highly experienced member of the Siemens Safety team."

For the Tunstead automatic crane project, the Siemens Safety team also recommended the use of the Siemens Industry Safety Evaluation Tool (SET) to provide the calculations and documentation.

Lafarge Tarmac's Mark O'Dwyer says: "Safety is at the core of our business, so the independent consultancy and support provided by the Siemens Safety team has been an invaluable back-up.

"It has given us a highly credible view and final validation on the safety systems in place for the automatic cranes, as well as the independent reassurance that we have complied with all legislative requirements."

The safety system is now in place and operating smoothly at the plant, with maintenance tasks on the automatic cranes performed within a safe working environment.

Brian Tinham

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