|
You may know something about BS EN ISO 13849-1 already, or you may know just that it is the replacement for BS EN 954-1. But there may be things that you do not know, and there are some things about BS EN ISO 13849-1 that are causing confusion. This article is written for people involved with machine safety (including specifiers, designers and end users) and aims to tell you what you need to know.
What is the legal status of BS EN ISO 13849-1?
This is the British version of an International standard and it is harmonised to the Machinery Directive. In other words, if you comply with the standard, you are deemed to be complying with the essential health and safety requirements (EHSRs) of the Machinery Directive, which is necessary if a machine is to be CE marked prior to it being placed on the market in Europe.
BS EN ISO 13849-1 (Safety of machinery, Safety-related parts of control systems, Part 1: General principles for design) is replacing the much simpler BS EN 954-1. The new standard was harmonised to the Machinery Directive on 8 May 2007, yet the old standard remains current until 31 December 2011. In other words, until that date, machine builders are entitled to choose which standard to use.
Is anyone using BS EN ISO 13849-1 yet?
So long as BS EN 954-1 remains current, many people will continue to use this simpler standard because it will be quicker and, therefore, cheaper. However, BS EN 954-1 is not really suitable for complex machinery or safety-related control systems using programmable safety controllers, so if these use electrical safety-related control systems, it would be wiser to use another standard, BS EN IEC 62061 (Safety of machinery. Functional safety of safety-related electrical, electronic and programmable electronic control systems). Because BS EN IEC 62061 only relates to electrical systems, complex safety-related systems using, say, pneumatics or hydraulics should be designed to the new BS EN ISO 13849-1. But don't forget that Type C standards (ie those relating to specific groups of machinery) take precedence, so it might be that one of these can be used instead, thereby avoiding the complexity within BS EN ISO 13849-1.
Is there a 'risk graph' in BS EN ISO 13849-1
The 'risk graph' in BS EN 954-1 was sometimes criticised as being an over-simplification, yet it was easy to use and well understood. A similar process is used within the new standard but, instead of leading the user towards a Safety Category, the standard refers to Performance Levels. Unfortunately, these Performance Levels do not align neatly with either the Safety Categories of BS EN 954-1 or the SILs (safety integrity levels) of BS EN IEC 62061.
The performance level (PL) is determined from the category (structural requirement), the desired mean time to dangerous failure (MTTFd), the diagnostic coverage (DC) and common cause failure (CCF). This involves a series of calculations and requires certain data to be available from the suppliers of safety-related components.
Six steps to take
BS EN ISO 13849-1 introduces a six-step approach for designing, verifying and validating the safety-related parts of a machine control system:
Step 1 - Define the safety function requirements (ie identify all of the features required from each safety function).
Step 2 - Determine the required performance level PLr (this is where the 'risk graph' is used to establish the Performance Level required in view of the risks involved).
Step 3 - Design and technical realisation of the safety functions (the designer can decide what system architecture and components could be used to achieve the necessary safety functions identified in Step 1).
Step 4 - Determine and evaluate the performance level (this requires component performance data to be obtained from the manufacturers in order to calculate the Performance Level achieved by the proposed system).
Step 5 - Verification (does the Performance Level achieved in Step 4 match or exceed the required Performance Level from Step 2? If not - or if the system appears to be 'over-engineered' and potentially too expensive - the design output from Step 3 can be revisited).
Step 6 - Validation (EN ISO 13849-1 offers a simplified approach to the validation of software functions, recognising that more intuitive programming/configuration software is likely to result in fewer programming errors).
Are there any shortcuts?
A simplified procedure for estimating the Performance Level is described in the standard, and this refers to five defined 'designated architectures'. These designated architectures show a logical representation of the system structure for each category and fulfil specific design criteria and behaviour under a fault condition. By using one of the designated architectures, users are spared the need to calculate the Performance Level.
Learning more about the standard and actually applying it to one or more projects will help to make the standard more familiar and easier to work with. Several companies are currently offering training courses and seminars, and there are also software utilities available to assist with performing calculations. As usual with machinery safety, the advice is to seek assistance unless you are sure you know what you are doing.
Of course, the first step in designing any machinery safeguards is to undertake a risk assessment. Procter Machine Guarding offers a free Risk Assessment Calculator that is available for free. Just send an email to
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
Back to Machine Safety Newsletter
|
