Safety instrumentation alarms

More and more commonly, fire alarm panel data is transferred to a safety instrumented system (SIS) for graphic annunciation though the SIS human-machine interface (HMI). 

Alarms, process safety interlocks, and safety instrumented systems can be modified easily by aging or tampering and such critical safeguards are just too vital to neglect. Each organization must develop an effective way to ensure that process safety systems will properly function when the process demands protection. 

The Safety Instrumented Systems (SIS) and critical alarms assigned a Class 1 include those that have been mandated as such by state or federal agencies an in-house technical safety review committee HAZOP studies and specific alarms deemed critical by operations supervisors. All of these Safety Instrumented Systems and alarms are on a regular prooftesting schedule. 

Class 1 safety instrumentation loops include alarms and trips on storage tanks containing flammable or toxic liquids, devices to control high temperature and high pressure on exothermic-reaction vessels, and control mechanisms for low-flow, high-temperature fluids on fired heaters. Other Class 1 instruments include alarms that warn of flame failure on fired heaters, and vapor detectors for emergency valve isolation and sprinkler-system activation. All of these alarms, shutdown valves, and other critical instruments are regularly proof-tested to a well-defined schedule. 

When a fault tree has been constructed, it can be used to estimate the probability of the system failing if the probabilities of the events in the fault tree can be estimated. In most cases, this requires a good understanding of the reliability of instruments, alarms, and safety devices, since these devices would be expected to maintain the process in a safe condition. 

The actions not needed to prevent the hazardous condition that may be of benefit for operational reasons. Such actions may include presentation of alarms, shut down of upstream or downstream units to reduce demands on other protection systems or actions that will enable fast start up once the cause of the hazard has been eliminated. It is important to separate these actions from the actions necessary to prevent the hazardous condition so as to minimize costs and restrict the boundary of the safety instrumented... 

The BPCS operator interface may be used to provide automatic event logging of safety instrumented functions and BPCS alarming functions. 

Safety instrumentation and alarms Start-ups and shutdowns Management of change Permit to work Contractor management Emergency management Compliance with standards. 

Procedural safeguards rely upon people either to trigger an automated safety system or to carry out the response to an ongoing situation. For example, if an operator is expected to respond to an instrument alarm, say high level in T-lOO, then his or her response constitutes a procedural... 

Alarms with defined operator response Critical alarms Safety instrumented systems Pressure relief devices Blast walls and dikes Deluge systems Flare systems... 

Remember that the BPCS operates with signals that are relatively dynamic. This makes BPCS failures generally detectable by plant personnel. Example diagnostic methods include flat line outputs, quality indicators, pre-alarms, deviation alarms, and out of range signals. While a BPCS operates under relatively dynamic conditions, safety instrumented system signals are static Boolean variables. Since the SIS only takes action when a potentially dangerous condition is detected, it can be very hard for operations and maintenance persormel to detect certain failure modes of a SIS. 

Many never consider a person to be part of a safety instrumented function. When reviewing the definitions used in functional safety standards, there is little indication that this was ever intended. A process operator takes action when normal process operating conditions are violated. The operator normally responds to these violations from alarms. The operator action is, therefore, normally considered as being part of the alarm layer of protection, not the SIS. 

Combined instrument safety airbag alarm lamp failure... 

Control System (BPCS), including functions of Supervisory Control and Data Acquisition (SCADA) system, the alarm system (AS) and Safety Instrumented Systems (SIS) performing defined Safety Instrumented Frmetions (SIF). Proper design of layers of protection is based on hazards analysis and risk assessment with consideration of human and organizational factors. It is essential to ensure required safety integrity level (SIL) for each of these layers. 

The present paper considers the safety of different systems or components. A safety instrumented system (SIS) is a system which consists of sensors, logic solvers and actuating items. The sensors may for instance be gas detectors, the logic solver could be a computer and the actuating items may be shut down valves. A fire and gas detection system with an alarm or a sprinkler system is an example of a SIS. A SIS is constructed to take the process into a safe state if a dangerous event occurs. 

Instrumentation for temperature control, feed control, safety, fire alarm, steam PRY... 

Where the above actions depend on an operator taking specific actions in response to an alarm (for example, opening or closing a valve), then the alarm shall be considered part of the safety instrumented system (i.e., independent of the BPCS). 

Alarms for which an operator or facility worker is required to evacuate an area (e.g., fire and gas alarms) and are not intended to direct the operator to take action on the process are generally not considered safety instrumented functions. These alarms should not be allocated to the BPCS but may be allocated to the SIS or to another independent protection layer. Refer to Annex F, Figure F.1, for an overview of protection layers. These alarms are generally classified as safety-related and are designed and managed in a manner that supports the allocated risk reduction. 

P.7.1 Immediately initiate the Safety Instrumented Function (vote channel to trip) on diagnostic alarm... 

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