In industries like oil and gas, chemicals, pharmaceuticals, and power generation, safety is not just a regulatory checkbox — it’s a core element of sustainable, reliable operations. Every day, companies work to reduce risk, protect their workforce, safeguard the environment, and maintain public trust.
At the heart of many of these efforts is functional safety, and a central tool in functional safety is the Safety Instrumented System (SIS). An SIS monitors critical process conditions and, when needed, automatically takes protective actions to bring the process to a safe state. To define the reliability required from each safety function, organizations use the Safety Integrity Level (SIL) framework.
However, even the most advanced safety system will fail if not properly maintained. Without regular calibration and proof testing, an SIS can degrade, leaving operations vulnerable to hazards. This blog post explains SIS, SIL, functional safety, calibration practices, global standards, and how companies can strengthen their safety programs.
For those wanting a deeper dive, we also invite you to download more detailed white paper on this topic. Also, we include a link to a webinar recording we did with ISA.
Download a more detailed white paper on this topic >
Watch webinar recording: For those interested in deepening their understanding, we recommend watching the recorded webinar co-hosted by Beamex and the International Society of Automation (ISA), featuring functional safety expert Paul Gruhn. This session provides valuable educational insights into SIS fundamentals, standards, and real-world challenges. Watch the webinar recording >
In high-risk industries like oil and gas, chemicals, and power generation, safety isn’t just about ticking regulatory boxes — it’s essential for keeping operations running reliably and protecting people and the environment.
One of the most important frameworks behind industrial safety is functional safety, and at its core lies the Safety Instrumented System (SIS). SIS is designed to detect dangerous conditions and automatically take action. To ensure these systems work as intended, each safety function is assigned a Safety Integrity Level (SIL).
But even the best technology won’t deliver results without proper maintenance and calibration. In this blog, we’ll explore what SIS and SIL really mean — and why calibration plays a critical role in keeping these systems safe, compliant, and audit-ready.
A Safety Instrumented System (SIS) is an independent system designed to monitor and automatically control hazardous process conditions. It is made up of:
Unlike the Basic Process Control System (BPCS), which manages routine operations, the SIS is designed to handle extreme conditions.
For example, if pressure in a chemical reactor rises beyond safe limits, the SIS may automatically close isolation valves and shut down feeds to prevent a rupture or explosion.
The independence and reliability of the SIS are crucial because it is often the last line of defense when other systems fail.
The image below is a screenshot from a recent webinar we hosted in collaboration with the International Society of Automation (ISA), featuring functional safety expert Paul Gruhn. It illustrates how the SIS is an independent system, separate from the basic process control system (BPCS). Watch the webinar recording >.
At a recent user group meeting in Australia, Jason Lang, an Electrical Engineer from Stanwell Corporation, presented how they use the Beamex solution for their SIS calibrations. In his presentation, he included the image below to explain the structure of the SIS:
Functional safety ensures that automatic systems detect and respond to unsafe conditions, reducing risks to acceptable levels. It’s about making sure protective systems — like the SIS — work correctly and reliably when called upon.
A key framework in functional safety is the safety lifecycle, which includes:
Importantly, functional safety does not stop at commissioning. Without regular calibration, proof testing, and maintenance, even the best-designed systems can degrade, leaving the facility vulnerable to hidden risks.
The Safety Integrity Level (SIL) is a performance measure assigned to a Safety Instrumented Function (SIF) — a specific protective loop within the SIS. SIL helps define how reliably that function must work to achieve the desired risk reduction.
There are four SIL levels:
SIL determination is part of risk assessments like HAZOP (Hazard and Operability Study) or LOPA (Layer of Protection Analysis). The assigned SIL guides design decisions, equipment selection, system architecture, redundancy, and testing intervals.
For example, a SIL 2 loop protecting a pipeline overpressure event may need annual proof tests, while a SIL 3 emergency shutdown loop on a high-pressure reactor may require semi-annual testing and redundant sensors.
SIS and SIL systems are critical across industries where equipment failures can have catastrophic consequences:
In each sector, the SIS is a crucial safeguard protecting lives, assets, and business continuity.
Several international and national standards govern SIS and SIL:
Compliance with these standards is not optional — it’s required by regulators and critical for legal, operational, and reputational protection.
Calibration and proof testing ensure that SIS components function reliably when needed.
Calibration in SIS environments can be challenging due to harsh conditions, confined spaces, and hazardous areas. Intrinsically safe, multifunction calibrators and well-trained technicians are essential.
Challenges in the field
Maintaining a robust SIS calibration program can be challenging. Field conditions are often harsh, with exposure to extreme temperatures, vibration, and corrosive environments. Access to devices may require confined space entry or working at height. Technicians must be well-trained, using intrinsically safe, accurate equipment, and following standardized procedures.
End-to-end vs. part testing
Proof testing of SIS components can be approached in two primary ways:
Ideally, part testing should overlap or complement other component checks to ensure full loop coverage. Whether testing end-to-end or in parts, the goal is the same: confirm that every component performs as required and that the safety function will execute correctly when needed.
There is no fixed “annual” calibration rule for SIS devices. Instead, intervals are set based on:
Example intervals:
Companies can sometimes adjust intervals based on performance data and risk analysis, but these decisions must be well-documented. Auditors increasingly expect companies to defend their calibration programs with evidence, not assumptions.
SIS calibration records are regularly audited by:
Auditors typically review calibration schedules, as-found/as-left results, test records, and management of change processes. Strong, traceable calibration programs are essential to pass these audits and maintain compliance.
Effective SIS calibration programs include:
Beamex delivers a comprehensive ecosystem of tools and services to help companies meet the demanding requirements of SIS calibration.
SIS and SIL are central to modern industrial safety programs. While design and technology are critical, it’s the ongoing calibration, proof testing, and maintenance that keep these systems reliable over their lifecycle.
A robust calibration program helps companies maintain compliance, reduce risk, improve performance, and protect their reputation.
Download a detailed white paper that explores SIS, SIL, calibration strategies, global standards, regulatory frameworks, and best practices — all designed to help you strengthen your safety programs.
Download the detailed free white paper here >
For those interested in deepening their understanding, we recommend watching the recorded webinar co-hosted by Beamex and the International Society of Automation (ISA), featuring functional safety expert Paul Gruhn. This session provides valuable educational insights into SIS fundamentals, standards, and real-world challenges.
Watch the webinar recording here >
If you need any help managing the calibration and documentation of your Safety Instrumented Systems, don't hesitate to contact our experts >