Single failure

Cooling water system corrosion causes immediate and delayed problems. Difficulties spread from a failure like ripples from a pebble thrown into a pool. A single failure may force an unscheduled outage, redirect worker efforts, contaminate product, compromise safety, increase equipment expense, violate pollution regulations, and decrease productivity. 

Boolean equations show how component failures can fail a system. A minimal cut. he smallest combination of component failures that can fail a system. It is the set of non-sup us components, such as in the previous example, with the superfluous combination Y Z(X Y,. Z) e uded. If they all occurred they would cause the top event to occur. One-component minimtil cut s( if there are any, are single failures that cause system failure. Two-component minimal cutsets ai tairs of components, if they occur together cause system failure. Triple-components minimal Cl sts are sets of three components that, if they fail together cause system failure, and so on to hi er cutsets... 

A single failure criterion is used in all quadrants of o,-02 space instead of the segments in separate quadrants for the Tsai-Hill failure criterion because of different strengths in tension and compression. 

It should be noted tliat FMECA identifies single failure modes tliat eitlier directly result in or contribute significantly to important accidents. Human/operator errors are generally not examined in a FMECA however, tlie effects of a misoperation are usually described by an equipment failure mode. It should also be noted that FMECA is not efficient for identifying combinations of equipment failures tliat lead to accidents. 

The seven single failures causing moderate release of toxic vapor... 

A major advantage of the fault tree approach is that it begins with a top event. This top event is selected by the user to be specific to the failure of interest. This is opposed to the event tree approach, where the events resulting from a single failure might not be the events of specific interest to the user. 

Failure Modes and Effects Analysis (FMEA) Scenario- based Inductive By component Mechanical/electrical systems Best for analyzing effects of single failures, although capable of developing and analyzing multiple-safeguard scenarios Looks at all failure modes of all components Higher... 

Another consideration in developing connection details for blast resistant structures is the provision for redundant load path. Because these elements may be stressed near their ultimate capacity the possibility of single failures must be considered. Where possible, it is desirable to provide an alternate load path should a failure occur. Consideration should be given to the number of components in the load path and the consequences of single failures. The key concept in the development of these details is to trace the load or reaction through the connection. This is much more critical in blast design than in conventionally loaded structures. 

Multiple layers of protection are a concept incorporated in the American Chemistry Council Process Safety Code of Management Practices. ) Management Practice number 15 endorses sufficient layers of protection through technology, facilities, and personnel to prevent escalation from a single failure to a catastrophic occurrence. This approach can be applied to multiple system root causes when the investigation team evaluates... 

All in-plant lots are being held in quarantine until a final decision is made concerning any potential impact on the quality of products prepared to date. However, a review of historical data collected under current conditions indicates that we have not had a single failure in sterility testing performed on 100% of the 2918 lots manufactured in the past fifteen (15) months [including at least ten (10) lots of the new fill size]. These tests were conducted in full accordance with the requirements of 21 CFR 610.12 and have been validated with respect to sensitivity in identifying minimal levels of contamination. 

The flare header, which collects the vapors from the safety valves for safe discharge to the knockout drum and the flare stack, is sized for the largest vapor load caused by a single failure. This vapor load is obtained from a tabulation of relief loads from safety valves connected to the flare system. The loads which may occur simultaneously as a result of fire, cooling water failure, etc., are summed up. From these summations the largest load is determined. 

FYom the multitude of intricate corrosion processes in the presence of mechanical action (friction, erosion, vibration, cavitation, fretting and so on) it is justified to touch upon corrosion types joined under a single failure mode induced by mechanical stresses. These are the stresses that govern the corrosion wear rate of metals during friction. Such processes are usually called corrosion stress-induced cracking in the case that the mechanical action is effective only in one definite direction, or otherwise termed corrosion fatigue in the case that compressive and tensile stresses alternate within cycles. In spite of the differences between the appearance of these corrosion types, they have much in common, e.g. fundamental mechanisms, the causes, and they overlap to a certain degree [19]. 

The most important consideration in the evaluation of corrosion-related failure is safety, that is, whether the failure causes a loss of life or of function or secondary damage that could have adverse effect on operating safety. A critical failure is any failure that could affect adversely the safety of operation of both the equipment and the operating personnel. The term, direct effect, implies certain limitations. The impact of the failure must be immediate if it is to be considered direct. Further, the consequences must result from a single failure and not from a combination of the failure with another that is yet to occur. If a failure has no resultant effect on the system, it cannot by definition have a direct effect on safety. 

Fault-tolerance (including single failure criterion) SPINLINE 3 can meet any redundancy requirements. 

The Failure Mode and Effects Analysis (FMEA) is a systematic, bottom-up method of identifying the failure modes of a system, item, function and determining the effects on the higher level. It may be performed at any level within the system (e.g., piece-part, function, blackbox, etc,). Software can also be analyzed qualitatively using a functional FMEA approach. Typically, a FMEA is used to address failure effects resulting from single failures [1]... 

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