Specific hazardous event

In ANSI/ISA-84.00.01-2004 (lEC 61511 Mod), 3.2.71, a safety instrumented function is defined as a "safety function with a specified safety integrity level which is necessary to achieve functional safety." This standard, 3.2.68, defines a safety function as a "function to be implemented by a SIS, other technology safety-related system or external risk reduction facilities, which is intended to achieve or maintain a safe state for the process, with respect to a specific hazardous event."... 

Emphasis should be placed on the last phrase of the SIF definition, "specific hazardous event." This phrase helps one clearly identify what equipment is included in the safety instrumented function versus auxiliary equipment not actually needed to provide protection against the hazard. 

It seems logical to list the following equipment for this safety instrumented function pressure transmitter, logic solver, inlet feed valve, pump control relay, and outlet isolation valve. However, for each piece of equipment ask the question, "Is this piece of equipment needed to protect against the specific hazardous event " In this case, the pump is turned off just to protect the pump from backpressure burnout. (NOTE - This may be part of another safety instrumented function.) The outlet isolation valve is closed in order to avoid process disruptions in the remainder of the plant. Neither is required to protect against the hazard and should not be included in the SIF verification calculation. The pump control relay may be part of another SIF intended to protect the pump. However, it is likely that this SIF may have a lower safety integrity requirement. 

Since a Safety Instrumented Function is designed to prevent or mitigate a specific hazardous event it is also very important that those involved in SIL verification imderstand which and how many components have to operate successfully for the function to be effective. 

It is therefore essential that the inputs and outputs associated with all Safety Instrumented Functions (SIF) be properly defined to address the specific hazardous event being prevented or mitigated by the SIF. Failing to do so will result in erroneous SIL verification results. 

The new approach is applicable for low demand SIFs, which are the most common SIFs in the od and gas industry. A low demand SIF is passive during normal operation and is intended to respond if a specific hazardous event occurs. In passive mode, limited information is available about the system state. Regular functional testing is therefore important to reveal failures that otherwise would be hidden until the next demand. The approach presented in this paper suggests criteria for how to adjust the functional test intervals, based on operational experience. 

Fault tree analysis is a technique by which the system safety engineer can rigorously evaluate specific hazardous events. It is a type of logic tree that is developed by deductive logic from a top undesired event to all subevents that must occur to cause it. It is primarily used as a qualitative technique for studying hazardous events in systems, subsystems, components, or operations involving command paths. It can also be used for quantitatively evaluating the probability of the top event and all subevent occurrences when sufficient and accurate data are available. Quantitative analyses shall be performed only when it is reasonably certain that the data for part/component failures and human errors for the operational environment exist. 

NOTE 1 The risk in this context is that associated with the specific hazardous event in which SiS are to be used to provide the necessary risk reduction (i.e., the risk associated with functionai safety). 

The purpose of this annex is to provide guidance for establishing instrument setpoints for safety instrumented functions in the process industries. The scope of ANSI/ISA-84.00.01 is requirements for... a safety instrumented system, so that it can be confidently entrusted to place and/or maintain the process in a safe state." This annex provides guidance on instrument uncertainty calculations and setpoint determination for instruments used in an SIS to ensure that each SIF responds to achieve or maintain the safe state of the process within one-half of the process safety time with respect to a specific hazardous event. If measurement uncertainty is not considered in the determination of an SIS setpoint, the SIF may not detect the presence of a valid process demand. 

Function to be implemented by an E/E/PE safety-related system or other risk reduction measures, that is intended to achieve or maintain a safe state for the equipment under control in respect of a specific hazardous event. ... 

Safety function Function implemented by a safety instrumented system or other safety related technological system for reduction risk of the facilities, i.e. to achieve or maintain a safe state for the process, with respect to a specific hazardous event. 

The purpose of this annex is to provide an exampie of an outiine methodoiogy for the systematic identification of initiating events that can iead to hazardous events. This methodoiogy can be used with any SiL determination (such as LOPA, fauit tree anaiysis) or other techniques used for identification of the initiating events ieading to a specific hazardous event. 

Uniqueness - Designed to prevent/mitigate specific hazardous events. Does not have other functions In the normal operation of the facility. 

The severity of unmitigated consequences range from low to high and include both safety and environmental considerations. Unmitigated consequences are estimated by considering the harm that specific hazardous events can cause. 

Likelihood Likelihood defines in quantitative or qualitative terms, the estimated probability of the specific hazardous event under study. Likelihood is one element of associated risk (the other being severity). Fault trees and other models can be constructed and individual hazard probabilities are estimated, and likelihood can be calculated via Boolean Logic. 

The purpose of a what-if analysis is to identify hazards, hazardous situations, or specific accident events that could produce an undesirable consequence. The what-if analysis is described in detail in Guidelines for Hazard Evaluation Procedures (CCPS, 1992). 

The FTA method was originally developed to supplement a FMEA. Fault trees, in their original usage, were diagrams indicating how the data developed by FMEAs interact to cause a specific event. The FTA method is most effective in analyzing complex systems with a limited number of well-identified hazards. In most cases, FTAs are used to perform in-depth analyses of hazardous events identified by another hazard evaluation method. 

Consequences of contaminating hot and high boiling liquids with low boilers can be estimated using thermodynamics. If these scenarios are possible, relief valves should also be installed to mitigate these events, or adequate safeguards should be added to the system to prevent the specific hazard scenario. 

The accidental release of hydrogen fluoride is one of the most hazardous events in the laboratory due to the physicochemical properties of hydrogen fluoride1 213 and specifically its attack of living tissues (for a review of symptoms and treatment, see ref 315). 

Hazards of the materials being transported Specific initiating events that may be cortsidered Potential consequences and impacts while in transit Accident history Potential gaps in safety practices... 

The lower white diamond indicates specific hazards or information, such as oxidizer, acid, alkali, or radiation hazard, or may have a no water symbol, which means use no water in the event of fire. 

A strategy that makes easier for the team to handle with large nodes was proposed and the main initiating events identified during the Petrobras coke drums HAZOP analysis were presented. Some LOPA results were commented in order to provide the reader the type of answers this approach allows. These results include the identification of the logics that need to be defined as safety instrumented functions and the required target SIL to achieve a tolerable frequency of occurrence for a specific hazard scenario. 

Loss of the propulsion function by a ship is one of the most serious categories of hazardous events in shipping. In specific external conditions it may lead to a loss of ship together with people aboard. The loss of propulsive power may be an effect of the propulsion system (PS) failures or of errors committed by the crew in the system operation process. In the safety engineering language we say that the propulsion loss probability depends on the reliability of the PS and of its operators. 

Hazard probability The aggregate probability of occurrence of the individual hazardous events that create a specific hazard (MIL-STD-882). 

A description of the potential hazard and recommended actions to be taken by emergency and firefighting personnel dnring a fire or explosion event for a specific hazard, location, or facility based on previons inspections and surveys of identified hazards. Pre-fire plans note the structural features, physical layout, special hazards, installed protection systems, fire hydrant locations, water supplies, and similar features pertinent to firefighting operations. Pre-fire plans should be routinely updated or revised as changes occur in a facility or location. 

Many techniques are available to estimate the frequency of a given type of major hazardous event occurring at a specific facility, on a transportation corridor, or along a pipeline. (For detailed descriptions see TNO, 1988, and CCPS, 1989a, 1995b.) These vary in complexity and type of information they yield. Their selection depends on the desired outcome and the amount of time and effort available. The techniques we will consider are ... 

The specified action (fault reaction) required to achieve or maintain a safe state shall be specified in the safety requirements specification. It may consist, for example, of the safe shutdown of the process, or that part of the process which relies, for risk reduction, on the faulty subsystem, or other specified mitigation planning. The total time to detect the fault and to perform the action shall be less than the time for the hazardous event to occur. 

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