The consequences of equipment faults or process disturbances in the oil and gas industry range from minor issues to plant disaster. In the chain of events against accident escalation, the actual process system is the first link, followed by high quality containment (like nitrogen blanketing), gas detection and emergency shut down (ESD), isolation of ignition sources, ventilation, fire detection and ESD, area separation firewalls / passive fire protection, active fire protection, escape / evacuation.
Fire and gas detection, fire prevention and fire extinguishing are key elements used to limit damage resulting from process system failures. The requirements for high availability with negligible probability for failure on demand are therefore essential as these systems will be idle, until needed.
Standards are an ever evolving necessity that helps focus our processes, product and system developments. These standards relate to hazardous area location, device / product and system performance. As yet there is no universal international standard for things like hazardous area classification. IEC Ex is a step in the right direction, but as yet countries appear slow to adopt.
Product performance approval, once conducted by many of the major oil and gas operators has been increasingly pushed to third party agencies although there seems little sign of global standardisation.
There does however seem to be some progress regarding the implementation of systems for design and maintenance of safety related applications. IEC61508/61511 defines the safety integrity level (SIL), where the main focus is their probability to fail on demand. Although traditionally applied to the process system they are being increasingly applied to the fire and gas detection systems.
As systems become more sophisticated, it is important that the total cost of ownership is considered. The actual unit price for a detector is insignificant compared to the installation cost and maintenance cost over a period of say 10 years, let alone the cost of an unnecessary shut down due to a false alarm or an extinguishing system failing to engage.
Trends in these areas described briefly:
One of the first links in preventing a fire incident is to remove the oxygen present. Nitrogen generators can be used to fill empty voids in tanks or systems holding volatile compounds. Nitrogen can be replaces can fill the space where oxygen may be present thus removing one of the three elements in the fire triangle (fuel / heat / oxygen).
Fire and gas detection
Combustible gas detection has seen a change a marked shift in technology over the past 10 years. The majority of high-end users deploy infrared detectors, where practical, due to improved reliability and reduced maintenance. These devices also tend to be faster and immune to poisoning compared to catalytic detectors.
Maintenance systems are evolving to collect statistics from field devices by digital interfaces like HART and Foundation Fieldbus. Maintenance can therefore be planned to increase systems up-time, as well as reduce the maintenance costs.
The next major step for fire and gas detectors is the introduction of laser technology for things like H2S detection. Open path laser detectors need less maintenance, are fail safe and respond faster to an incident than traditional detection techniques.
Prompt fire extinguishing reduces the general damage to property whilst protecting site personnel. Over recent years these methods have evolved both in terms of performance and environmental impact. This has involved a transition from using lots of water, chemicals and noxious gases to pure water and personnel safe inert gases. In general the challenge is to extinguish a fire before it escalates into a major incident, thus limiting casualties and damage. The extinguishing solutions employed are always tailored to match the anticipated fire type. In many applications, fast detection and then extinguishing to control damage is essential. Low pressure water mist has enjoyed increasing popularity recently, even for outdoor installations, as a limited amount of pure water can knock down / control, high energy fires.
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About Odd R Gilinsky
He is the Product Line Manager for field instruments in the Simtronics Group, Detection Systems Division. He is an engineer in electronics from education with a wide background in special communication networks (offshore, power utility, pipelines, air traffic control) and the last four years in product management of infrared gas detectors.