Explain like I'm five · Law/Policy

What is a Functional Safety Standard (ISO 26262, IEC 61508)?

Functional safety standards, told as a story about the student council giving every field's own claim of "it's safe" one shared grading scale and an independent check.

our school bus brakes are totally safe!our automatic door was called safe tooevery field has its own idea of what "safe" means

Every field has its own idea of what "safe" means.Different words for "safe" can't be compared against each other.

every supplier says something different — which do we trust?our class's automatic door suddenly wouldn't stopwith only claims and no shared standard, the danger shows up only after an accident

Without a shared standard, suppliers' safety claims can't be compared or trusted.With only claims and no shared standard, the danger shows up only after an accident.

functional safety standard = a shared rulebook that grades risk and sets matching safeguardsTHE SHARED RULEBOOKIEC 61508 — the base rulebook for many fieldsISO 26262 — rewritten specifically for carsSIL/ASIL — higher grade, higher riskhigher grades need more independent checksthe standard gives every field's own "it's safe" the same kind of grading scale

A functional safety standard is a shared rulebook that grades risk and sets matching safeguards.The standard gives every field's own "it's safe" the same kind of grading scale.

Base standard (IEC 61508)where many fields start from
Domain-specific standard (ISO 26262)rewritten specifically for cars
Grading (SIL/ASIL)higher risk gets a higher grade
Independent checksomeone separate from the makers checks it
IEC 61508 (base)ISO 26262 CARSASIL grades A–Dfor buses and carsIEC 61511 PROCESSSIL grades 1–4for chemical plantsIEC 62061 MACHINERYSIL grades 1–3for factory machinesmany fields rewrite IEC 61508 into their own specific standard

Domain-specific standards branch out from the base standard.Many fields rewrite IEC 61508 into their own specific standard.

every safeguard for the grade is in placebut the equipment still needs watching and checkingmeeting a grade doesn't bring risk to zero, so analyses like FTA and FMEA and checks go on

Even certified, the risk of accidents never reaches zero.Meeting a grade doesn't bring risk to zero, so analyses like FTA and FMEA and checks go on.

In one breath

Functional safety standards = safety rulebooks built on the common base, IEC 61508, then rewritten and specialized for a domain like automobiles (ISO 26262), using risk grades (SIL/ASIL).

IEC 61508 is a general international standard covering functional safety of electrical, electronic, and programmable electronic systems, grading risk with SIL (Safety Integrity Level) 1 through 4. ISO 26262 specializes this for the automotive industry, using ASIL (Automotive Safety Integrity Level) A through D and setting requirements across the vehicle's entire lifecycle — planning, design, verification, production, and decommissioning. Higher grades demand stricter development and verification processes and more independent confirmation. Third-party certification isn't an ISO 26262 requirement: some companies stop at self-assessment, and others get certified because a customer asks.

When grown-ups say it

Functional Safety Standard
A shared rulebook that grades risk. Rewritten into domain-specific versions in many fields.
IEC 61508
The base standard many fields start from. Covers electrical and electronic systems broadly.
ISO 26262
The standard specialized for automobiles. Rewrites IEC 61508 specifically for cars.
SIL (Safety Integrity Level)
A risk-based grade, 1 through 4. Used by IEC 61508 and several industry-specific standards.
ASIL (Automotive Safety Integrity Level)
The automotive-specific grade, A through D. A grading scheme unique to ISO 26262.
Third-Party Certification
Not declaring safety yourself — getting it checked from outside. Not always required by the standard, but a customer may ask for an outside body's check.
Risk/Safety Analysis
The techniques that find risks before a grade is even assigned. FTA, FMEA, and HAZOP handle this analysis. → tracing an accident backward — or scanning for it ahead of time
Software/Functional Safety (General Concept)
The general principle that higher risk means more layers of checking. This page covers the standard hierarchy — the general idea lives in another field. → the book where one typo weighs differently
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