ISA84 Fire and Gas Systems

 In Fire and Gas Engineering

A critical concern to anyone involved in the Oil and Gas industry is the need to maintain a high level of process and plant safety. Alongside these safety concerns is the need for producers to reduce costs especially in these tightened economic times. One way to do this is by minimizing damage to equipment and eliminating incidents that impact people and the environment. This also can help maintain a positive image, as it can show that a company is aware of its corporate responsibility and acts accordingly.

A Fire and Gas System (FGS) is key to maintaining the overall safety and operation of industrial facilities. A FGS continuously monitors for abnormal situations such as a fire, or combustible or toxic gas release within the plant; and provides early warning and mitigation actions to prevent escalation of the incident and protect the process or environment. By implementing an effective and optimized FGS design based on the latest methodology and technology, plants can meet their plant safety and critical infrastructure protection requirements while ensuring operational and business costs are kept in check due to this optimization.

Background

Throughout the process industries, plant operators are faced with risks. For example, a chemical facility normally has potential hazards ranging from raw material and intermediate toxicity and reactivity, to energy release from chemical reactions, high temperatures, high pressures, etc. According to international standards, safety implementation is organized under a series of protection layers, which include, at the base levels, plant design, process control systems, work procedures, alarm systems and mechanical protection systems. The safety instrumented system is a prevention safety layer, which takes automatic and independent action to prevent a hazardous incident from occurring, and to protect personnel and plant equipment against potentially serious harm. Conversely, the FGS is a mitigation safety layer tasked with taking action to reduce the consequences of a hazardous event after it has occurred. The FGS is used for automating emergency actions with a high-integrity safety and control solution to mitigate further escalation. It is also important for recovering from abnormal situations quickly to resume full production.

Safety Bow tie example with FGS included

Safety Bow tie example with FGS included

Challenges

Producers must cope with business challenges ranging from increased accident, incident and insurance costs, to compliance with strict prescriptive standards and codes such as NFPA 72, EN 54, API, OSHA, and CSA.

Plants are looking for ways to improve safety by increasing the FGS effectiveness, and reduce costs through optimization. Optimization can lower costs by lowering the upfront system capital investment and reduce the cost of ownership for safety equipment. Many facilities are also dealing with the cost of upgrading and refurbishing existing, non-integrated FGS’s.   Facilities are discovering needs such as the requirement of the FGS to have communications integration with the DCS in order to have FGS graphics and alarms for display to the operator, while also requiring independent displays such as independent HMIs to draw attention to fire & gas excursions when the DCS HMIs are not available. The plant FGS, along with fire system for occupied buildings, should be integrated with Plant Evacuation and System/Site Security Centre for plant evacuation.

FGS Architecture

FGS Architecture

Safety Standards and FGS implementation

Industrial Standards are playing a large role in developing, implementing and installing FGS’s. The development of the ISA84 / IEC 61511 standard was a major step forward when it comes to increasing safety within the industrial environment. The overall safety lifecycle model described in the IEC standard lists all of the necessary project activities, from the concept (identification) phase to the decommissioning phase, necessary to ensure the functional safety of equipment under control. These activities can be divided over a wide range of categories such as procedures, documentation, testing and validation, planning, hardware and software development, and risk assessment.

Since a FGS is such an important safety system within a plant, many practitioners were trying to apply these international safety standards to help engineer a more effective FGS. This led to many questions being raised as to how the FGS mitigation layer could be engineered to comply with the standard, since most of the standard tended to deal with the preventive safety layer. The location of the detection devices, and the effectiveness of the mitigation after FGS activation was not contained within the standard. There have been discussions over whether the FGS should contribute to risk reduction or be considered as a protection for the installation only.

These questions lead to the creation of an ISA84 technical report TR84.00.07 in 2010, which was designed to provide guidance on the evaluation of fire & gas system effectiveness. This document contains information about how FGS differs from SIS design, and discusses the Detection Coverage, and Mitigation Effectiveness in addition to the actual hardware reliability. Instead of the traditional prescriptive methods used to design a FGS, It takes a more risk based engineering approach to measure the effectiveness of the design. The basic risk formula is stated to be: Risk = Probability x Consequences , and moving towards this risk analysis method of FGS engineering allows this critical safety system to have a measurable risk mitigation component when it comes to the overall plant safety philosophy.

A new draft of ISA84 TR84.00.07 is currently under review and expected to be released sometime late 2015/early 2016. This will include many more real work examples and clear up definitions and methods currently included within the TR. The overall goal of the development group is to turn this TR into an international standard, and this is progressing. As of 2014, IEC standard 60079-29-3:2014 – Explosive atmospheres – Part 29-3: Gas detectors – Guidance on functional safety of fixed gas detection systems includes a clause that references ISA84 TR84.00.07 as a valid method for FGS engineering.

FGS engineering methodology

The safety lifecycle defined in the ISA Technical Report TR84.00.07 for FGS is very similar to the one defined for safety instrumented systems in the IEC61511 standard. Risk scenarios must be identified before a FGS can be designed for a particular application. The hazards and consequences associated with each scenario must be analyzed taking into account the impact on human lives and assets. It is also important to consider the frequency of occurrence of the consequence   while making decisions on the FGS design. If it is anticipated that the consequence will occur quite frequently, then a more rugged risk mitigation system needs to be considered.  The steps that should be completed in order to get the full benefits from the ISA TR84.00.07 are shown in figure 3.

FGS safety Lifecycle

FGS safety Lifecycle

 

Conclusion

The requirements to have a safe and effective Fire and Gas detection systems are increasing in the industry. With the advent of documents such as the ISA84 Technical Report TR 84.00.07, there is a way to move from the historical process of relying on vendor recommendations, rules of thumb and designing system “the way we have always done it” to a more provable engineered system. Potentially catastrophic releases happen all too frequently. As recent as March 20, 2015, an offshore platform in the North Sea was reported to have had a flammable gas leak for at least 84 minutes, undetected.

In order to have a measurably safe facility, implementation of a safety instrumented systems may be required. Calculations can be done on a SIS to determine the Safety Integrity Level (SIL), but a SIS is only capable of preventing the consequence from occurring. Even if a risk analysis determines that a SIS is not required, some sort of FGS will invariably be needed as the potential for a release or fire can be present in any process environment, due to corrosion, metal fatigue, human error, and a host of other factors. FGS’s are capable of mitigating the consequence of those releases or fires. This mitigation component greatly complicates their analysis.

The ISA84 Technical Report TR 84.00.07 provides recommendations for the design of fire and gas detection systems within industrial areas having serious hazards. The technical report finally gives safety professionals a guide as to how to engineer a Fire and Gas system in a way that give you measurable safety factors, and allows for FGS optimization in order to reduce costs without compromising safety.

Greg Pajak is an independent safety and risk consultant, can be found at www.seitechnologies.ca

REFERENCES

ISA84-TR84.00.07-2010 – “Guidance on the Evaluation of Fire, Combustible Gas and Toxic Gas System Effectiveness” ” Version 1, January 2010.

  1. IEC 60079-29-3:2014 – Explosive atmospheres – Part 29-3: Gas detectors – Guidance on functional safety of fixed gas detection systems, June 2014
  2. Fire and Gas Systems Engineering Handbook, first edition (2013) – Kenexis Consulting Corporation

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