In-depth safety system validation for cement plant

22 April 2014

Adhering to legislative requirements is an essential part of modern production processes, in particular corporate responsibility to ensure the provision of a safe working environment for employees. Siemens Industry worked with Lafarge Tarmac at its Tunstead Cement Plant in the UK during a modernisation project to provide independent consultancy support to the site’s in-house engineering team and help ensure compliance with the safety-led requirements of the Machinery Directive 2006/42/EC.

The upgrade project was to provide safe employee access during maintenance processes to two automatic cranes used to handle raw materials such as aggregates.  While the in-house team took responsibility for all the PLC programming, including the distributed safety functions, they turned to long-standing partner Siemens Industry to assist with third-party validation around the software from a safety perspective.

In-depth risk assessments were undertaken to ensure compliance with all safety standards and the Siemens Safety team provided a final independent sign off for all documentation in accordance with the requirements of the Machinery Directive 2006/42/EC Technical File Documentation.
Howard Stott of Siemens Industry explained further: “We have had a strong working relationship with the engineering team at the Tunstead site going back to 2003, which includes a service contract.  On this particular safety-led project our initial discussions highlighted the fact that the engineers were using the Hazard Rating Number (HRN) scoring method for Risk Assessment and Risk Reduction measures.  A recommended way of determining the Safety Integrity Level (SIL) and Performance Level (PL) levels is by tasking layers of personnel to undertake the assessment so that multiple views are recorded and then combining the results for the best overall level of safety performance.”
To provide the additional level of increased scrutiny on the safety performance and to support the in-house system designers who were using Siemens products, the Siemens Safety team was contacted to perform a further assessment of the software system both in terms of its structure and to ensure it reflected the recommendations as published in manuals from Siemens.  It was asked to cover three principle areas.  Firstly, assessment of the safety-relevant application software supplied by Lafarge Tarmac against the operating instructions and product manuals.  Secondly, an assessment of the safety-relevant application software programming techniques with respect to the functional safety standard BS EN 62061, and finally, advise on any additional diagnostics mechanisms and measures for the system.
Stott continued: “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.  Assessment work of this kind can be performed off site as well as at the actual location, but the critical element is the independence of the expert and 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 for the safety systems, including the technical file.  With all Siemens’ product data built-in for the products used on this project - as well as third party products - the SET tool has clearly assisted in the overall evaluation and validation process on site.
Mark O’Dwyer for Lafarge Tarmac 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 for the in-house team.  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 all maintenance tasks on the automatic cranes performed within a safe working environment ensuring high availability and operational efficiencies are optimised.

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