Fire and gas systems, while present in many plants, are often poorly understood by personnel at these facilities. They are considered complex and the subject of a few specialists. Yet, although these systems may appear tricky, operators can greatly benefit from a better understanding of these systems and their parts. At the most basic level, fire and gas systems are designed to detect fires or unignited releases or combustible or toxic fluids, providing early warning of the incident by alerting operators and initiating an appropriate protective response. A system is comprised of software and hardware that together provide real-time monitoring of a specified zone.
Before a system can deploy safety actions, it must identify a hazard. This is accomplished by a variety of detection devices, known as fire and gas sensors, often installed in tandem to increase system reliability. To detect gas releases, one may use point or open path gas detectors. Point detectors may be catalytic or infrared (IR) type, used for detecting combustible gases, or electrochemical or solid-state for the detection of toxic gases and oxygen depletion. Ultrasonic gas leak detectors recognize the escape of pressurized gas by measuring acoustic emissions, which correlate the sound pressure level produced by the jetting gas to the mass flow rate.
Flames are detected using sensors that measure the intensity or frequency of radiant energy from the fire, usually in the ultraviolet (UV) or IR regime. Similarly, fires are identified using heat detectors or optical (photoelectric) smoke detectors.
On hazard recognition, the system initiates safety response. Common actions are alarms and evacuation or sheltering of personnel, automatic emergency shutdown with isolation and depressurizing equipment, automatic control of ignition sources, and activation of deluge systems to disperse gas or suppress fires. Typical components are horns, strobes, and automatic fire extinguishing devices like actuators for suppression systems.
It is important to remember that a system can only detect incidents that its sensing elements can access. Thus, the quantity, type, and location of sensors must be carefully selected given the plant environment and required level of risk reduction. Guidelines like the International Society of Automation’s report TR84.00.07 (Guidance on the Evaluation of Fire, Combustible Gas, and Toxic Gas System Effectiveness) aim to link the nature of probable hazards to the characteristics of the best safety system for the site.
To learn more about the role of fire and gas systems in your plant, view this plant safety video. Additionally, you may contact me via e-mail at Edward.Naranjo@emerson.com.
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