Machine Safety Directive

Changes in the Machinery Directive usher in the concept of “functional safety”.

How will the new Machinery Directive affect machinery standards? 

Which standard do you apply?

How will the new directive affect component suppliers?

Q. How will the new Machinery Directive affect machinery standards? 

The standard used to design safety control circuits, BS EN 954-1 is being withdrawn. You may be familiar with this standard and the categories (B, 1, 2, 3 and 4), which related to the behaviour of a safety circuit under fault conditions and the circuit architecture. In the past there has been a tendency for safety components specified to a high category of BS EN 954-1 to be chosen instead of components that have a lower category, but might actually have more suitable functions.

Two new “functional safety” standards have been added:

• BS EN 62061
• BS EN ISO 13849-1

These will encourage designers to focus more on the functions that are necessary. This will reduce each individual risk on a machine and help understand what performance is required for each function, rather than simply relying on particular components.

The performance of each safety function is specified as either as:

• SIL (Safety Integrity Level 1,2 or 3) in the case of BS EN 62061
• PL (Performance Level a, b, c, d or e) in the case of BS EN ISO 13849-1

In both cases the architecture of the control circuit, which delivers the safety function is a factor, but unlike BS EN 954-1 these new standards require consideration of the reliability of the selected components.

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Q. Which standard do you apply? 

BS EN 62061 is perhaps more comprehensive and is more applicable to safety systems incorporating programmable safety components where software is involved.

BS EN ISO 13849-1 is designed to allow an easier transition from BS EN 954-1.

Full explanation of these two standards, together with some worked examples for you to compare are found in our Safe Machinery Guide.

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Q How will the new directive affect component suppliers? 

The functional safety standards demand consideration of the reliability of the safety components, so we must provide reliability data required for the verification of the performance of the safety function.
Such reliability data includes:

• MTTFd (mean time to dangerous failure)
• PFH_D (probability of failure on hourly demand)
• B10 (used to calculate MTTFd or PFH_D)
• DC (Diagnostic Coverage)
• %SFF (safe failure fraction).

Reliability data is used in conjunction with the circuit architecture to calculate the overall SIL or PL of the safety channel being designed.

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Our support can supply you with the data you require upon request.