MAC


MACHINE SAFETY


SAF ETY FEAT R E FEA ATURE


Update to standard for safety relate d controls on machines


to the Machi ery Directive. David Col er of


T


he planned merger of EN ISO 13849-1 and EN 62061 into


IEC/ISO 17305 by the Joint Working Group JWG1 did not eventually come to pass, however, during the attempt an official request was made to alter the existing version of EN ISO 13849-1 which did take place in December 2015. The latest 2015 edition is now harmonised to the Machinery Directive.


The modifications are in some cases purely editorial (suc h as t h


elsewhere being replaced b suffix ‘d’ used in MTTFd , B


however, some important clarifications and shifts have been


that EN ISO 13849-1:2015 i included, and it is now the


go-to standard for safety- controls on machines since the previous edition is no longer harmonised to the Machinery Directive 2006/42/EC.


related s the case


y ‘D’),


10d and e


pact these changes will have happened in section 4, Design


Considerations. In section 4.5.2 the limitation of MTTFD to 100 years (capping) was previously applicable to all subsystems


regardless of category, which had the undesirable effect of limiting the number of category 4 subsystems which could b e combined without a drop in


Performance Level from PL e to PL d. This was thought to be too conservative, therefore, for


limit has been raised to 2,500 years which means later in the informative annex K the table K1 now covers this extended range instead of 100 years.


The update to BS EN ISO 13849-1, thiird edition 2015 - standard for safety related controls on machines, is now harmonised to the Machinery Directive. David Collier of Pilz U


The update to BS EN I O 13849-1, th edi on 2015 - standard for safety related control on machi es,


now harmonised


ilz UK shares his observations of the impact these changes wi have


shares his observations of the


a new statement is made about non-failsafe PLCs whose manufacturer-developed


embedded firmware does not meet the requirements of SRESW (safety related embedded software needs to be developed in accordance with


detailed task only eve IEC 61508-3 which is


r conducted a very


by safety PLC/controll manufacturers). The r


equirement er


is that for standard PLCs to be used in safety functions the PL


In section 1 the table comparing the recommended application o f EN ISO 13849-1 and EN 62061 has been removed, but EN 62061 is still mentioned. In section 2 normative references to other


assessment and risk reduct as ISO 12100:2010 for risk


In section 3 (terms and ion.


In section 4.5.4 the assumption made for Category 2 that the demand rate must be less than 1/100 of the test rate has been changed to “the demand rate is less than or equal to 1/100 test rate; or testing occurs immediately upon demand of the safet y function and the overall time to detect the fault and to bring the


category 4 subsystems the cappi ng must be limited to PL a or b when in Category B, 2 or 3, and for PL c or d to be achieved two diverse PLCs must be used in two channel architecture. In practise such as structure would not be used due to installation and maintenance


efforts (two different PLCs running together) and probably also space and cost. Therefore, for PL c and above and above the obvious choice is to use safety PLCs.


definitions) one addition is the mention of “proven in use” which means demonstration, based upon operation experience for a specific configuration of a component tha t a likelihood o f a dangerous failure is low enough not to impact the Performance Level of all safety functions incorporating that


component. Later in the standard it becomes clear in 4.5.5 that this is only “allowed” for mechanical,


where omission of MTTFD i hydraulic and pneumatic el


ements s to be


justified, and proven in use would need to be stated by the


manufacturer of the component. Quite a lot of change has


standards have been updated, such machine to a non-hazardous condition (usually to stop the machine) is shorter than the time to reach the hazard (see also ISO 13855)”. The added possibility to test “on demand” allows a dual channel category 2 design with one active channel and onemonitoring channel, the latter recognising and appropriately responding to


demand placed on the former, bu t only actively getting involved in the case that the first channel fails. This could be useful for retrofit applications (second channel as an add-on to the existing first channel), if timing constraints are met to ensure that for safety distances are maintained with respect to stopping times (see also EN ISO 13855).


Section 4.6 covers software and /AUTOMATIONATION /AUTOMAT


In section 6.2.2 reference is still made to the fact that the structure (Category) is the key characteristic having the greatest influence on the PL. The statement that it is admissible to design according to a machine-specific C-standard specifying just a Category (as was in EN 954-1) and not the PL (hence obviating the need to consider MTTFD, DC and CCF) has been removed.


There aremany other changes, but the above are some of themost significant. The fact that this new edition is harmonisedmeans tha t software tools, such as PAScal v1.8 have been updated to reflect these changes More details, including changes to the informative Annexes, are available on the Automation website at


. connectingindustry.com/automation


Pilz Automation T: 01536 460766


T: 01536 460766 www ilz.co ww.pilz.com AU AUTOMA MAT ATION | DECEMBER/ DECE R/J/JANUARY 201 2017 29 29


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