1. How to develop E/E/PESs to IEC 61508?
E/E/PES is:
electrical/electronic/programmable electronic system
IEC subclause 3.3.3

2. What is the safety question?
How to make a product safe, or
How to make a safe product?

3. What is safety?
How do you measure it?

4. Safety: “freedom from unacceptable risk”
Harm to:
probability of
occurrence
people
property
environment
safety
people
property
severity of
occurrence
environment

5. What is a Risky System? A system with an unacceptable combination of:
probability of occurrence of harm
and
the severity of that harm.

6. IEC 61508 safety theory is - remove systematic defects
IEC implies:
ad hoc or non-safety processes  non-safety products
non-safety processes – systematic defects  safety processes
safety processes  safety products
safety processes + functional safety assessment  IEC compliance

7. The Safety Equation MTBF = MTBRF + MTBSF PFD = PRFD + PSFD
safety integrity = hardware safety integrity + systematic safety integrity
MTBF - Mean Time Between Failure MTBRF - Mean Time Between Random Failure MTBSF - Mean Time Between Systematic Failure
PFD - Probability of Failure on Demand PRFD - Probability of Random Failure on Demand PSFD - Probability of Systematic Failure on Demand

8. failure rate = RHF + SHF + SSF
Safety Measurements
MTBF = 1/(failure rate)
failure rate = RHF + SHF + SSF
SIL  1/(failure rate)
SIL  1/(RHF + SHF + SSF)
RHF - Random Hardware Failure SHF - Systematic Hardware Failure SSF – Systematic Software Failure SIL - Safety Integrity Level
See IEC , Tables 2 and 3

9. Relationship of IEC 61508 to failure type
random hardware failure (RHF) see IEC
systematic hardware failure (SHF) see IEC
systematic software failure (SSF) see IEC

10. Systematic defects
Systematic defects are removed during the product development lifecycle
The product development lifecycle is depicted graphically with the V-model
The V-model for software development is shown in Figure 5 of IEC

11. The Parts of IEC 61508 IEC 61508-1 Part 1: General requirements
IEC Part 1: General requirements
IEC Part 2: Requirements for electrical/electronic/programmable electronic safety-related systems
IEC Part 3: Software requirements
IEC Part 4: Definitions and abbreviations
IEC Part 5: Examples of methods for the determination of safety integrity levels
IEC Part 6: Guidelines on the application of IEC and IEC
IEC Part 7: Overview of techniques and measures

12. Non-complex or Complex system?
Non-complex  deterministic system
A deterministic system has a unique output for each specific input
Complex  non-deterministic system
A non-deterministic system means that the system output is a function of the current input and the previous output.

13. IEC 61508-3 Software Requirements Example
From the E/E/PES hardware development processes, it has been determined that a microcontroller is required to implement the complex logic in software, (See IEC Figure 1) and SIL 3 has been determined
IEC , clause 7.2, Software safety requirements specification,
points to IEC , Table A.1
IEC , Table A.1, Software safety requirements specification,
points to IEC , Technique/Measure B.2.4
IEC , Technique/Measure B.2.4,
describes Computer-aided specification tools

14. WHY NOT ENGINEERING