Impact of the New International Safety Standards

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Impact of the New International Safety Standards
Chris Leahy
Impact of New International Safety Standards
Chris Leahy Commercial Product Manager - Safety
Sensing NHP Electrical Engineering Products Pty
Ltd
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New Terms
ISO 61508
MTTF - Meantime to Dangerous Failure
IEC 62061
AS 4024.1
SRP/CS - Safety related parts of a control system
EN954.1
SIS - Safety Instrumented Systems
SIL - Safety Intergrity Level
SRCF - Safety related control function
ISO 13849
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A Brief History

• As a result of the requirement for
• Automation
• Demand for increased production
• Reduced operator physical effort
• Safety Related Electrical Control Systems (SRECS)
• Of machines play an increasing role in the
  achievement of overall machine safety.
• Previous reluctance due to uncertainty of the
  performance of the technology

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Summary of EN 954-1

• EN 954-1 Safety of Machinery
• Applies for all safety related parts a control
  system, regardless of the power supply
• Electric
• Hydraulic
• Pneumatic

• Deterministically defines categories
• Each category identifies the system requirements
  and behaviour in the event of a fault.
• Simple to determine how an electromechanical
  system might fail
• Machine is built to shut down in the event of a
  fault or part failure

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Criticisms' of EN 954-1

• Modern programmable equipment is complex, and
  may fail in unexpected ways with consequences
  impossible to predict!
• EN954-1 does not
• Despite being applicable for programmable systems
  and complex electronics, it contain any detailed
  requirements
• Inadequately reflects the increasing complexity
  of factory automation
• No relibability considered
• Assumes the risk to an operator is always
  constant
• Does not contain any special requirements for
  Software Design
• No account for a distinguishing between an
  individual machine or an integrated production
  system.

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Failure to Adjust

• As standards should keep up with technological
  progress the Normalisation bodies (CEN) paid
  particular attention to E/E/PES during the
  revision process of EN954-1.
• Failure to adjust?
• ISO (CEN European Committee for Standardisation)
  and IEC (CENELEC European Committee for
  Electrotechnical Standardization ) would drift
  further apart both prepare voluntary standards
• Could effect free trade between countries
• Would increase the confusion for both the
  mechanical engineers, designers and machine users
• Challenging Standards?
• ISO 13849 adopted as the successor
• IEC 62061 more detailed/complex standard but
  only considers E/E/PES
• Both are Harmonised Standards under the Machine
  Directive considered to have achieved the
  directives essential safety requirements

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Hierarchy
EN ISO 13849.1
Replacing EN954.1 as the General design
guidelines Scope Electrical, electronic and
programmable electronic control systems E/E/PES,
hydraulics, pneumatics, mechanics
Functional safety of safety-related
E/E/PES Outlines the tools and formulas to
calculate the probability that safety functions
will fail and then provides a system of SIL
levels to categorise these systems.
EN 61508
Safety of machines functional safety of safety
related E/E/PES and instrumentation as a
scientific approach, it dictates how the
statistical results obtained in EN 61508 are
applied to machinery.
EN 62061
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Why the Result

• In our opinion ISO 13849 is proving more
  successful as
• IEC 62061
• is too complicated
• only rates electrical systems
• aimed at the component manufacturer

• ISO 13849
• Focuss on the establishment of categories
  traditional
• Contains special requirements for SRP/CS with
  programmable electronic systems
• A reference regardless of the technology and
  energy form used (electric, hydraulic, pneumatic,
  mechanical etc)

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Compilation

• Deterministic designing the system and relying
  on the design to be right
• Probabilistic the statistical probability of an
  unwanted occurrence or failure

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ISO 13849-1

• ISO 13849-1
• Forces you to validate that the control system
  does what is required of it
• CC Control CAT deterministic - required
  system behaviour when a fault occurs
• PL Performance Level probabilistic -
  represent different average probability values of
  a failure to danger per hour

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A Brief History