Functional safety
IEC 61508
The basic functional safety standard for E/E/PE safety-related systems and the parent of IEC 61511 and IEC 62061.
Functional safety of electrical/electronic/programmable electronic safety-related systems
- Category
- Functional safety
- Scope
- International
- Edition / refs
- IEC 61508:2010, Parts 1–7
MSA output
- SIL verification
- FTA · FMEA · Bowtie analysis
- Proof test records
- Full traceability
What is IEC 61508?
IEC 61508 is the basic functional safety standard for electrical, electronic and programmable electronic (E/E/PE) safety-related systems. It is the parent of sector standards including IEC 61511 (process industry), IEC 62061 (machinery) and ISO 26262 (road vehicles), and it is applied directly by manufacturers of safety-related devices such as transmitters, logic solvers and valves.
It defines an overall safety life cycle and four Safety Integrity Levels. Targets are expressed as the average probability of failure on demand (PFDavg) for low-demand mode, and the average frequency of dangerous failure per hour (PFH) for high-demand or continuous mode — alongside architectural constraints and systematic capability requirements.
Who it applies to
- Manufacturers developing SIL-capable devices and subsystems
- Designers of E/E/PE safety systems where no sector standard applies
- Integrators and end users relying on device SIL claims under IEC 61511 or IEC 62061
- Functional safety engineers and assessors
Key requirements
- 01
Safety life cycle
Manage every phase from concept and hazard analysis to decommissioning, as defined in IEC 61508-1.
- 02
Functional safety management
Competence, planning, verification and independent functional safety assessment.
- 03
SIL targets
Low demand: SIL 1 to SIL 4 correspond to PFDavg bands from ≥10⁻² to <10⁻¹ down to ≥10⁻⁵ to <10⁻⁴. High demand: PFH bands from ≥10⁻⁶ to <10⁻⁵ down to ≥10⁻⁹ to <10⁻⁸ per hour.
- 04
Hardware safety integrity
Quantify random hardware failures and meet architectural constraints, via Route 1H (hardware fault tolerance and safe failure fraction) or Route 2H (field reliability data).
- 05
Systematic capability
Apply techniques and measures to avoid and control systematic faults in hardware (Part 2) and software (Part 3).
- 06
Diagnostics and proof testing
Account for diagnostic coverage, proof test interval and proof test coverage in PFDavg and PFH calculations.
Summary for orientation only. Always refer to the current official text of IEC 61508 and any applicable legislation.
MSA for IEC 61508
What MSA generates
Evidence produced from your engineering inputs, traceable end to end and exported to Word, PDF or Excel.
SIL verification
Calculations and records for each safety function against its SIL target.
FTA · FMEA · Bowtie analysis
Deductive and inductive analyses that support hardware safety integrity arguments.
Proof test records
Proof test procedures and results tied to the functions and assumptions they verify.
Full traceability
From hazard to safety function to verification evidence, regenerated when inputs change.
Frequently asked questions
Do I need IEC 61508 or IEC 61511?
Process-industry end users, designers and integrators of safety instrumented systems normally work to IEC 61511. IEC 61508 applies to manufacturers of the devices used in those systems, and to applications where no sector standard exists.
What is the difference between low demand and high demand mode?
In low demand mode the safety function is demanded no more than once per year, and integrity is expressed as PFDavg. In high demand or continuous mode it is demanded more often than once per year, and integrity is expressed as PFH.
Does MSA certify devices to IEC 61508?
No. MSA generates engineering analysis and evidence to support your functional safety work. Product certification to IEC 61508 is carried out by an independent certification body.
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