HAZOP studies for gas mixing plants: Systematic safety analysis for process plants

Gas mixing systems are indispensable in numerous industries, such as the chemical, glass, steel and automotive industries. They enable the precise production of gas mixtures that are required for processes such as shielding gas applications, fuel gas supply or the addition of hydrogen in the energy transition. If flammable or toxic gases are used, such systems are associated with considerable safety risks.

To minimize these risks, conducting a hazard and operability study (HAZOP) is an established procedure. This article highlights the importance, process and results of HAZOP studies specifically for gas mixing plants and draws on the expertise of companies such as LT GASETECHNIK and the weyer group as well as established standards and procedures.

A HAZOP study is a systematic, structured procedure for identifying and evaluating potential hazards and operating problems in process plants. Developed in the 1970s by the British chemical industry, it is used worldwide in accordance with the DIN EN 61882 standard. In Germany, the procedure is also known as PAAG (Prognosis, Detection, Assessment, Countermeasures). The aim is to detect deviations from the intended operating state before they lead to accidents, plant damage or environmental pollution.

HAZOP studies are also relevant for systems that work with hazardous substances such as flammable gases (e.g. hydrogen, propane, SO2) or other potentially hazardous substances. They are a central component of safety documentation and support conformity with EU directives and standards such as IEC 61508 and IEC 61511 for functional safety.

The primary objective of a HAZOP study is to systematically identify potential hazards and malfunctions, analyze their causes and effects and define suitable countermeasures. For gas mixing plants, this means minimizing risks such as leaks, overpressure, incorrect gas compositions or explosions. The study not only serves the safety of employees and the environment, but also the availability and reliability of the plant. It also provides support in defining safety requirements, such as the Safety Integrity Level (SIL), which is required by the operator to safeguard critical systems.

A HAZOP study is carried out in several steps and uses an interdisciplinary team of experts, e.g. from process engineering, safety engineering, electrical engineering and mechanical engineering. The process is methodical and follows a clearly defined scheme:

1. Preparation: First, the system is divided into so-called nodes (subsections). All relevant documents, such as flow diagrams (P&ID), operating instructions and substance data sheets, are provided.
2. Analysis with key words: The team uses standardized key words (e.g. “none”, “more”, “less”, “reverse”) in combination with process parameters (e.g. pressure, temperature, flow) to identify potential deviations.
3. Assessment: The causes, potential effects and existing protective measures are analyzed for each deviation. The team checks whether additional measures are required, e.g. technical or organizational precautions.
4. Documentation: The results are recorded in a detailed report containing all identified deviations, their evaluation and recommendations for measures. This report serves as the basis for the implementation of safety improvements.

The duration of a HAZOP study depends on the complexity of the plant. Several days may be required for a medium-sized gas mixing plant, depending on the number of nodes and the risk assessment.

The results of a HAZOP study are a comprehensive report and specific recommendations for action. Typical measures for gas mixing plants include, for example

• Installation of additional safety devices, such as gas analyzers or pressure relief valves
• Implementation of redundant control systems, e.g. for flow control or shutdown systems
• Adaptation of operating procedures, e.g. through training for operating personnel
• Definition of SIL levels and use of SIL fittings and SIL circuits for safety-critical systems to ensure the reliability of protective functions

A practical example: For a propane/air gas mixing system with a capacity of 42 MWh/h, manufactured by LT GASETECHNIK, a HAZOP study in accordance with DIN EN 61882 determined that the system has a fundamentally safe design. Nevertheless, potential hazards were identified. A SIL 2 circuit with oxygen gas analyzer, differential pressure monitoring and shut-off valve were implemented as countermeasures. These measures ensure safe operation and minimize the risk of explosion in the event of impermissible oxygen enrichment in the gas mixture.

Another practical example is the development of lean air systems for the production of synthetic resins, where HAZOP studies define SIL 1 or SIL 2 protection. These systems operate with low oxygen levels (4-10%) to prevent deflagrations in potentially explosive atmospheres. The HAZOP analysis led to the implementation of gas analyzers and redundant controls that significantly increase process safety.

As a member of the weyer gruppe, LT GASETECHNIK benefits from comprehensive expertise in the field of plant safety. The weyer gruppe, a group of companies with over 200 employees in Germany, Austria, Poland and Switzerland, has been active in the planning and safety analysis of process plants since 1976. Every year, the group realizes over 1,000 projects in industries such as chemicals, pharmaceuticals and energy. The weyer group offers HAZOP studies as an officially recognized procedure, which is also relevant for projects in the field of hydrogen technology and gas mixing lines. http://weyer-gruppe.com/hazop-ein-gewinn-an-sicherheit/ Thanks to this cooperation, LT GASETECHNIK has access to a broad network of safety engineers and can also efficiently implement complex safety requirements.

LT GASETECHNIK is a leading manufacturer of high-performance gas technology systems, gas mixers and fittings based in Dortmund. The company offers customized solutions for industrial applications, e.g. dynamic gas mixing systems for H2/N2 protective gas in the flat glass industry, gas mixing systems for steel and light metal production or refinement, or systems for natural gas/hydrogen mixtures in the energy transition as well as gas mixing systems for fuel gases (e.g. propane/air as a natural gas substitute). HAZOP studies are an integral part of the company’s safety and documentation processes, especially for plants with flammable or toxic gases.

HAZOP studies for gas mixing plants ensure

• Compliance with legal requirements, e.g. the Industrial Safety Regulation and ATEX directives.
• Minimizing risks for personnel, plant and the environment.
• Optimization of system availability through preventive measures.

The IEC 61508 and IEC 61511 standards play a key role here, as they define the requirements for functional safety. HAZOP studies provide the basis for defining SIL levels, which ensure that protective systems such as shutdown systems or gas analyzers function reliably.

HAZOP studies are a tool for improving the process safety of gas mixing plants. By systematically identifying and evaluating potential hazards, they help to prevent accidents, ensure the safety of employees and the environment and safeguard plant availability. HAZOP studies for gas mixing plants are regularly used to develop customized, safe solutions for industrial applications.