SIL determination vs SIL verification — what's the difference?

Determination sets the target SIL a function needs (usually via LOPA). Verification proves the as-designed function achieves it, through PFD calculation. You need both.

IEC 61508 or 61511 — which applies to me?

61508 is the general/manufacturer standard; IEC 61511 is the process-industry application standard. Most operating sites are assessed against 61511.

Do I really need a Safety Requirements Specification?

Yes — IEC 61511 requires it, and it's one of the most common gaps we find. No SRS means no defensible basis for what your SIS should do.

How does proof-test interval affect my SIL?

Strongly — the same hardware can meet or miss target depending on test frequency. We recommend intervals that keep you in target without over-testing or forcing spurious trips.

Can you verify an existing SIS, not just new design?

Yes — much of our work verifies installed systems on operating plants and finds where real performance falls short of the rated SIL.

Functional Safety Consultant Malaysia

SIL determination, verification and the full IEC 61511 lifecycle, so your safety instrumented systems deliver the protection they're rated for & you're not paying for safety that isn't actually there.

The PISB Approach

Your team works safer and more efficiently with manuals they can actually understand.

What is functional safety (SIL)?

Functional safety is the protection delivered by your safety instrumented systems (SIS) — the sensors, logic solvers and final elements that move a process to a safe state when something goes wrong. The Safety Integrity Level (SIL 1–4) measures how reliably a given safety instrumented function (SIF) performs that job, expressed as its average probability of failure on demand (PFDavg). Under IEC 61508/61511, functional safety is the discipline of determining the SIL each function needs, then proving the installed design actually achieves it.

A "SIL 2" certificate on a datasheet protects no one

Plenty of plants carry a SIL-rated valve on a datasheet and assume they’re covered. But SIL is a system property, not a component sticker. It depends on architecture and redundancy (1oo2, 2oo3), proof-test interval, common cause failure, and real field failure data. A function can fall short of its target the day it’s commissioned & you’d never know until it failed to act on demand. The cost of that discovery is measured in incidents, not invoices.

There’s a second, quieter cost: over-engineered functions and excessive proof testing that drain maintenance hours and force spurious trips that take production offline. Right-sizing SIL works both ways enough integrity to be safe, not so much that you’re burning money and uptime.

We determine the SIL you genuinely need via LOPA, then verify your installed function meets it through PFD calculation closing the gap between the certificate and reality & recommending proof-test intervals that hold the target without over-testing.

Our functional safety services

SIL determination (LOPA-based)

Establishing the target SIL for each safety function from your hazard studies.

SIL verification (PFD calculation)

Proving the design meets target, accounting for architecture, redundancy and common cause failure.

Safety Requirements Specification (SRS)

The IEC 61511-mandated document most sites skip; without it, your SIS has no defensible basis.

Safety lifecycle & Functional Safety Assessment (FSA)

Governance across design, operate and maintain phases, through to validation.

FAQ

SIL determination vs SIL verification — what's the difference?
Determination sets the target SIL a function needs (usually via LOPA). Verification proves the as-designed function achieves it, through PFD calculation. You need both.
IEC 61508 or 61511 — which applies to me?
61508 is the general/manufacturer standard; IEC 61511 is the process-industry application standard. Most operating sites are assessed against 61511.
Do I really need a Safety Requirements Specification?
Yes — IEC 61511 requires it, and it's one of the most common gaps we find. No SRS means no defensible basis for what your SIS should do.
How does proof-test interval affect my SIL?
Strongly — the same hardware can meet or miss target depending on test frequency. We recommend intervals that keep you in target without over-testing or forcing spurious trips.
Can you verify an existing SIS, not just new design?
Yes — much of our work verifies installed systems on operating plants and finds where real performance falls short of the rated SIL.

Who We Work With

We have worked closely with many local and multi-national companies in Malaysia as well as overseas to fulfil their specific needs. Through recognised certification training, we help individuals and teams build the competency their roles and industries demand.