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CEN/TC 114, Safety of machinery, in collaboration with Technical Committee ISO/TC 199, Safety of
machinery, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna
Agreement).
This second edition cancels and replaces the first edition (ISO ISO 13849-1:1999), which has been technically
revised.
ISO 13849 consists of the following parts, under the general title Safety of machinery — Safety-related parts
of control systems:
Part 1: General principles for design
Part 2: Validation
Contents Page
Foreword............................................................................................................................................................. v
Introduction ....................................................................................................................................................... vi
1 Scope ..................................................................................................................................................... 1
2 Normative references ........................................................................................................................... 1
3 Terms, definitions, symbols and abbreviated terms......................................................................... 2
3.1 Terms and definitions........................................................................................................................... 2
3.2 Symbols and abbreviated terms ......................................................................................................... 8
4 Design considerations ......................................................................................................................... 9
4.1 Safety objectives in design.................................................................................................................. 9
4.2 Strategy for risk reduction................................................................................................................. 11
4.2.1 General................................................................................................................................................. 11
4.2.2 Contribution to the risk reduction by the control system .............................................................. 11
4.3 Determination of required performance level (PLr)......................................................................... 14
4.4 Design of SRP/CS ............................................................................................................................... 14
4.5 Evaluation of the achieved performance level PL and relationship with SIL............................... 15
4.5.1 Performance level PL ......................................................................................................................... 15
4.5.2 Mean time to dangerous failure of each channel (MTTFd) ............................................................. 17
4.5.3 Diagnostic coverage (DC) .................................................................................................................. 18
4.5.4 Simplified procedure for estimating PL............................................................................................ 18
4.6 Software safety requirements ........................................................................................................... 21
4.6.1 General................................................................................................................................................. 21
4.6.2 Safety-related embedded software (SRESW) .................................................................................. 21
4.6.3 Safety-related application software (SRASW) ................................................................................. 22
4.6.4 Software-based parameterization ..................................................................................................... 25
4.7 Verification that achieved PL meets PL r .......................................................................................... 26
4.8 Ergonomic aspects of design............................................................................................................ 26
5 Safety functions .................................................................................................................................. 26
5.1 Specification of safety functions ...................................................................................................... 26
5.2 Details of safety functions ................................................................................................................. 28
5.2.1 Safety-related stop function .............................................................................................................. 28
5.2.2 Manual reset function......................................................................................................................... 29
5.2.3 Start/restart function .......................................................................................................................... 29
5.2.4 Local control function ........................................................................................................................ 30
5.2.5 Muting function................................................................................................................................... 30
5.2.6 Response time .................................................................................................................................... 30
5.2.7 Safety–related parameters................................................................................................................. 30
5.2.8 Fluctuations, loss and restoration of power sources..................................................................... 31
6 Categories and their relation to MTTFd of each channel, DCavg and CCF.................................... 31
6.1 General................................................................................................................................................. 31
6.2 Specifications of categories .............................................................................................................. 32
6.2.1 General................................................................................................................................................. 32
6.2.2 Designated architectures................................................................................................................... 32
6.2.3 Category B........................................................................................................................................... 32
6.2.4 Category 1 ........................................................................................................................................... 33
6.2.5 Category 2 ........................................................................................................................................... 34
6.2.6 Category 3 ........................................................................................................................................... 35
6.2.7 Category 4 ........................................................................................................................................... 36
6.3 Combination of SRP/CS to achieve overall PL ................................................................................ 39
7 Fault consideration, fault exclusion.................................................................................................. 40
7.1 General ................................................................................................................................................. 40
7.2 Fault consideration ............................................................................................................................. 40
7.3 Fault exclusion .................................................................................................................................... 41
8 Validation ............................................................................................................................................. 41
9 Maintenance......................................................................................................................................... 41
10 Technical documentation................................................................................................................... 41
11 Information for use ............................................................................................................................. 42
Annex A (informative) Determination of required performance level (PLr) ................................................ 44
Annex B (informative) Block method and safety-related block diagram .................................................... 47
Annex C (informative) Calculating or evaluating MTTFd values for single components.......................... 49
Annex D (informative) Simplified method for estimating MTTFd for each channel ................................... 57
Annex E (informative) Estimates for diagnostic coverage (DC) for functions and modules.................... 59
Annex F (informative) Estimates for common cause failure (CCF)............................................................. 62
Annex G (informative) Systematic failure ...................................................................................................... 64
Annex H (informative) Example of combination of several safety-related parts of the control system .. 67
Annex I (informative) Examples ...................................................................................................................... 70
Annex J (informative) Software....................................................................................................................... 77
Annex K (informative) Numerical representation of Figure 5 ...................................................................... 80
Bibliography ..................................................................................................................................................... 83
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