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Glossary Term: Gain
1. Ratio of output signal magnitude to input signal magnitude; when less than one this is usually called attenuation. 2. The relative degree of amplification in an electronic circuit. 3. The ratio of the change in output to the change in input which caused the change. 4. In a controller,…
Glossary Term: Fusible plug
A hollowed threaded plug having the hollowed portion filled with a low melting point material. This element is often used to provide a mechanical relief device triggered by temperature causing the process fluid to vent when the plug material melts.
Glossary Term: Functional safety assessment
Activity performed by a competent senior engineer to determine if the safety system does meet the specification and actually achieve functional safety (freedom from unacceptable risk). This assessment is an important part of reducing systematic failures. It must be performed at least after commissioning and validation but before the hazard…
Glossary Term: Functional safety
Freedom from unacceptable risk achieved through the safety lifecycle. See IEC 61508, IEC 65111, safety lifecycle, and tolerable risk.
Glossary Term: Full variability language (FVL)
This type of language is designed for computer programmers and provides the capability to implement a wide variety of functions and applications Typical example of systems using FVL are general purpose computers. In the process sector, FVL is found in embedded software and rarely in application software. FVL examples include:…
Glossary Term: FMEDA
Failure Modes Effects and Diagnostics Analysis - This is a detailed analysis of the different failure modes and diagnostic capability for a piece of equipment. This is an effective method for determining failure modes and failure rates, a requirement for certification against IEC 61508 in most certification agencies. FMEDAx –…
Glossary Term: Flow straightener
A supplementary length of straight pipe or tube, containing straightening vanes or the equivalent, which is installed directly upstream of a flow meter for the purpose of eliminating swirl from the fluid entering the flow meter
Glossary Term: Floating ball
A full ball positioned within the ball valve that contacts either of two seat rings and is free to move toward the seat ring opposite the pressure source when in the closed position to effect tight shutoff
Glossary Term: Flash point
The minimum temperature where a liquid emits vapor in a concentration sufficient to form an ignitable mixture with air near the surface of the liquid but not sufficient to sustain combustion.
Glossary Term: Flammability
Susceptibility to combustion. flammable (explosive) limits The flammable (explosive) limits of a gas or vapor are the lower (LFL or LEL) and the upper (UFL or UEL) percentages by volume of concentration of gas in a gas-air mixture that will form an ignitable mixture
Glossary Term: Fixed program language (FPL)
This type of language limits the user to adjusting a few parameters (for example, range of the pressure transmitter, alarm levels, network addresses). Typical examples of devices with FPL are: smart sensors (for example, pressure transmitter), smart valves, sequence of events controllers, dedicated smart alarm boxes, and small data logging…
Glossary Term: Fireball
Result of a sudden and widespread release of a flammable gas or volatile liquid that is stored under pressure, coupled with immediate ignition. This is distinguished from a jet fire by the shorter duration of the event and the difference in the geometry and shape of the flame. When a…
Glossary Term: Fire (Pool)
Results when spilled flammable liquids are ignited. The magnitude of the effect zone created by a pool fire will depend on the size of the flame that is generated, which in turn depends on the size of the spill surface and the properties of the spilled fluid. The flame’s footprint…
Glossary Term: Fire (Jet)
Results when high-pressure flammable material is ignited as it is being released from containment. The effect zone of a jet fire is proportional to the size of the flame generated. As a high-pressure material is released from a hole, the material will exit with a velocity that is mainly a…
Glossary Term: Fire (Flash)
The result of ignition of a cloud of flammable vapor, when the flame velocity is too slow (laminar and subsonic) to produce an explosive shock wave. When a gas phase mixture of fuel an air is ignited, a flame front travels from the point of ignition in all directions where…
Glossary Term: Final element
Component of a safety function (such as a valve) which directly prevents the harmful event and brings the process to a safe state.
Glossary Term: Fault tree diagram
Probability combination method for estimating complex probabilities. Since it generally takes the failure view of a system, it is useful in multiple failure mode modeling. Care must be taken when using it to calculate integrated average probabilities.
Glossary Term: Fieldbus
A Fieldbus is a digital, two-way, multi-drop communication link between intelligent measurement and control devices. It serves as a Local Area Network (LAN) for advanced process control, remote input/output and high speed factory automation applications.
Glossary Term: Fault propagation modeling
The analysis of the chain of events that leads to an accident. By analyzing what events initiate that chain, which events contribute to, or allow the accident to propagate, and establishing how they are logically related, the event frequency can be determined. Fault propagation modeling techniques use the failure rates…
Glossary Term: Fault tolerance
Ability of a functional unit to continue to perform a required function in the presence of random faults or errors. For example a 1oo2 voting system can tolerate one random component failure and still perform its function. Fault tolerance is one of the specific requirements for safety integrity level (SIL)…
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