H‑Infinity

Safety Instrumented Systems (SIS) are the last line of defence in process safety. When basic process controls fail, the SIS detects dangerous conditions and takes automated action to bring the process to a safe state — preventing injuries, environmental damage, and equipment destruction. A properly designed SIS is not just a regulatory requirement; it's a commitment to protecting people, assets, and the environment.

01What are Safety Instrumented Systems?

A Safety Instrumented System comprises three integrated elements:

▸Sensors — Detect dangerous conditions (pressure, temperature, level, flow) using redundant, fail-safe measurement devices.
▸Logic Solver — Process input signals and execute pre-defined safety functions based on risk requirements.
▸Final Elements — Execute the safe action through shutdown valves, breaker tripping, or equipment isolation.

Together, these elements form a Safety Instrumented Function (SIF) designed to achieve a specific Safety Integrity Level (SIL) — typically SIL 2 or SIL 3 for process industries.

02Why SIS Matters

Process safety incidents have devastating consequences:

▸Human Cost — Process safety incidents can cause fatal injuries. A properly designed SIS prevents these tragedies.
▸Asset Protection — Uncontrolled overpressure, fire, or equipment failure can destroy multi-million-dollar assets. The SIS cost is a fraction of the potential loss.
▸Environmental Impact — Toxic releases and environmental damage from process upsets have long-term consequences. The SIS prevents release at source.
▸Regulatory Requirement — IEC 61511 and OSHA 1910.119 require risk assessment and SIS implementation where risk reduction is needed.

03Our Approach

We follow a lifecycle approach aligned with IEC 61511:

1. Hazard Analysis

Conduct HAZOP/LOPA studies to identify hazardous scenarios and determine required SIL ratings for each Safety Instrumented Function.

2. SIL Assignment

Assign Safety Integrity Levels based on risk reduction requirements, considering existing layers of protection.

3. SIS Design

Design redundant sensor-logic solver-final element architectures to meet required PFDavg targets with proven failure rates.

4. Validation

Verify that the designed SIS achieves required SIL through quantitative analysis (PFDavg calculations) and proof test procedures.

04Scope of SIS Services

Our SIS services cover the complete safety lifecycle:

▸SIL Assessment — HAZOP facilitation, LOPA studies, and SIL requirement determination.
▸SIS Design — Safety I/O listing, logic diagram design, sensor selection, and final element sizing.
▸Functional Safety Report — Comprehensive FSR documenting SIL calculations, PFDavg, and proof test procedures.
▸Commissioning & Validation — Factory acceptance testing, site acceptance testing, and validation documentation.

05Standards & Compliance

✓IEC 61511 — Safety Instrumented Systems

✓IEC 61508 — Functional Safety

✓ISA 84 — SIS Application

✓OSHA 1910.119 — PSM

06Why H-Infinity

Our functional safety team includes Certified Safety Professionals (ISP D/S) with experience on major process facilities across the GCC. We've performed hundreds of HAZOP studies, completed SIL assessments for refineries, petrochemical plants, and waste-to-energy facilities, and delivered SIS designs that have passed regulatory audits without comment. Our analysis is thorough, our documentation is complete, and our designs are proven in practice.

Safety Instrumented Systems (SIS)