To ensure process safety, you must understand functional safety management. However, that can be difficult. The world of industrial risk management is full of technical phrases, abbreviations, and standards. There is FMECA, HIPPS, QRA, LOPA, etc. But in this series of insights, we provide you with a basic introduction to some of the topic areas. First out: Functional safety is an integral part of process safety.
Imagine you are planning to design and build a new chemical plant. It's critical that there are automatic systems in place. This is because they can protect against leaks/spills that could be flammable, toxic, or hazardous in other ways. In addition, breakdown of equipment or accidents results in production stops (downtime). In this case, the plant owners cannot generate revenues for months or years. Hence, the design process for automatic safety systems, the so-called functional safety lifecycle, is fundamental to ensure that the risk is sufficiently low.
The core of functional safety is about defining requirements for instrumented safety systems and so-called safety instrumented functions, which normally include an input device, logic solver, and a final element. A pressure transmitter (input device) is a typical example of an instrumented function. It will react upon high pressure and send a signal to a programmable unit (logic solver). The programmable unit will send a signal to close a valve or stop a pump via, e.g., a circuit breaker or relay (final element) to prevent further pressure increase.
It will be possible to find suitable equipment (i.e., good enough to be part of the system) once you have defined the requirements. However, it's not sufficient that the design and component selection is good. Operate and maintain the equipment properly throughout the plant's lifetime. Therefore, you should regard functional safety as a lifetime activity. You typically perform it using the following steps:
THE STEPS TO FUNCTIONAL SAFETY MANAGEMENT
Step 1 – Defining the Framework for Functional Safety Management
Identify what standards apply to functional safety management. IEC 61508 (standard applicable for functional safety in all industries) and IEC 61511 (specifically for the process industry sector) are fundamental standards. Once you have defined the standards, the project should develop a Functional Safety Management Plan (FSMP) document. This document should provide a to-the-point framework and plan for how the project team will adapt and plan for functional safety.
If you intend to execute the project in multiple phases, e.g., Concept, Front End Engineering Design, and Detailed Design Phase, it is important to plan for and ensure the correct timing of, functional safety activities. A typical pitfall is to determine the final integrity and reliability requirements of instrumented safety functions too late in the procurement process after contracts and purchase orders are already set. Based on experience, if you have no plan for Functional Safety Management, you will most likely fail. So do not underestimate the importance of Functional Safety Planning. The plan could be very to the point and simple.
Step 2 – Identification of Risks
Perform a Hazard and Operability (HAZOP) Study, covering all critical systems, aligned with the FSMP from the previous step. Critical systems in this sense mean systems where an accidental scenario (e.g., leak, ignition, fire, mechanical damage, etc.) can result in personnel injury, environmental consequences, or major economic loss. A HAZOP is a structured assessment of a process system. The main intention is to verify that all hazards are identified and that the system is protected. A HAZOP should also cover operational scenarios as well as compliance with standards. HAZOP is also a very practical tool for the identification of scenarios for SIL Assessment – which is the next step.
Step 3 – Defining the Requirements
Apply a risk-based methodology to define the requirements for safety instrumented functions. You can allocate the integrity requirements per instrumented functions to ensure that you meet the acceptable risk level once you have an overview of all critical scenarios from HAZOP. For instance, assume there is a potential that a control valve could be driven closed and block the outlet from a pump. This could lead to an overpressure of the pump discharge and leaks to the surroundings (as identified by HAZOP). You could protect against this hazard by an instrumented function shutting off the pump on detected high pressure in the discharge, combined with a Pressure Relief Valve that will ultimately relieve the pressure to a safe location. The risk-based allocation process will then determine the requirements for the instrumented function.
If the instrumented function is defined as SIL 1, 2, 3, or 4, this determines the reliability and architectural requirements. We call such a function a SIF - Safety Instrumented Function. The higher the SIL value is, the stricter the reliability requirements are.
Step 4 - Procurement of Equipment
The Project team is responsible for procuring equipment accordingly, once you have given all instrumented functions SIL requirements. Additionally, to demonstrate that each instrumented function meets the requirements. This is not only related to probability calculations but also to the quality of the equipment itself. Typically, the vendors will provide safety manuals and SIL Certificates. A third party has usually confirmed that the equipment is manufactured in accordance with the standard. If a certificate or safety manual is missing for some reason, it would become necessary to investigate other ways (prior use/proven in use, etc.) to demonstrate “good enough”. Before you use them in safety applications, you need to confirm that the quality and reliability of the safety-critical components are good enough. That is basically the essence of step 4.
Step 5 – Verification Prior to Start-up
Confirm that you meet all the integrity requirements defined in the project phase. You need to confirm that you meet all the integrity requirements defined in step 3 before you start the plant (or individual system) and achieve steady operations. Hence, you need to include steps to verify that you meet the functional safety-related requirements in the commissioning phase. This could be response time requirements (e.g., how fast the system should act) or a test of basic fault-handling (to what state should the system go in case of a power outage?).
Step 6 – The Operational Phase of Functional Safety Management
Follow the performance of each safety instrumented function during operation. Once the plant is in operation, functional safety management is entering the most important and critical phase. During operation, you shall test each function at a regular interval (so-called proof test). You need to collect the data from the tests for data analysis. If the reliability of a function is worse than specified in the design phase, actions may be required. This could be related to a reduction of test intervals or the replacement of components. Ultimately, reduced performance of instrumented functions will increase the risk.
ORS Consulting is supporting stakeholders in multiple sectors with functional safety management. Any questions or comments?
