Non fail safe

Differential pressure control is a non-fail-safe control. Consider a reflux failure (e.g., reflux pump trips) in Fig. 19.12a. Pressure drop will fall, and the controller will call for more boilup. The use of a differential pressure control may thereby also enhance the column relief requirements (Sec. 9.7). 

Qhe design of the seismoscopes has a non-fail-safe characteristic which makes the two-out-of-two coincidence circuit very questionable from a reactor safety standpoint Power Failure Detection... 

A relay tripping circuit has been proposed by Manufacturing to eliminate the use of the electronic amplifier Ich exhibits non-fail—safe characteristics. This relay circuit is stxggested... 

A significant issue to address is the impact of "fail safe" versus "non fail safe" actuators. Some designs such as diaphragm and piston actuators with hydraulic and pneumatic power are readily available as spring return valves. The failure or release of control pressure permits the spring to drive the actuator to its safe position. 

Inspection and access "Fail-safe" components Non fail-safe (see notes below) components (see notes below) ... 

Non fail-safe structural components are such that local failure of one component could lead to failure of the structure or large sections of the structure. 

The ability to shutdown the process, independent of the BPCS controller and SIS logic, solver may be required for some applications. The current editions of NFPA 85 and NFPA 86 require independent means for equipment covered by these practices. The SIS logic solver has a very low failure rate, but what will you do when it fails Even with the very low failure rate, programmable electronic systems can fail. Equipment safety manuals may specifically require independence, especially for SIL 3 applications. When non-fail-safe design is used, e.g., energize to shutdown, independent shutdown facilities should be provided that do not require the SIF support system to be operational. 

Increase FT by 1 if SFF < 60% (normally applies to a non-fail-safe device to be avoided anyway). 

It generally is recommended, and often required, that gas dcicciiuii systems be installed in a fail-safe manner. That is, if power is disconnected or otherwise interrupted, alarm and/or process equipment shutdown (or other corrective action) should occur. All specific systems should be carefully reviewed, however, to ensure that non-anticipated equipment shutdowns would not result in a more hazardous condition tlian the lack of shutdown of the equipment. If a more hazardous situation would occur with shutdown, only a warning should be provided. As an example, a more hazardous situation might occur if blowout preventers were automatically actuated during drilling operations upon detection of low levels of gas concentrations than if drilling personnel were only warned. 

Wheel-speed sensors do not monitor speed directly they sense the movement of the circumference of the tire. This is done with 48 or 32 pulses per turn, and some correction factor for tire sizes. This information comes from driven and non-driven wheels, and means four independent sources of information describing road surface, friction coefficient, cornering etc. In all cases the information is passed through the electronic control unit (ECU). ABS and all advanced systems are safety systems that do not allow the electrical signal to be split before it goes to the ECU. This is necessary to make a fail-safe system. 

Accidents hke the Mars Polar Lander or the British batch chemical reactor losses, where the cause lies in dysfunctional interactions of non-failing, reliable components—i.e., the problem is in the overaU system design—illustrate reliable components in an unsafe system. There can also be safe systems with unreliable components if the system is designed and operated so that component failures do not create hazardous system states. Design techniques to prevent accidents are described in chapter 16 of Safeware. One obvious example is systems that are fail-safe, that is, they are designed to fail into a safe state. 

Nuclear safety I C systems have to meet demanding functional and non-functional objectives. They need high reliability and quality of components as well as good properties of architectures such as deterministic behavior, fail-safe and fault tolerant features, functional diversity, and separation. Furthermore, these systems should avoid unnecessary complexity and prevent when possible, operator and maintenance errors. In addition, safety I C systems shall meet the other customer expectations such as modularity, scalability, flexibility, ease of operation. 

Fission Product Retention Coated particle Pressure vessel unit Passive Passive/active Inherently safe fission product retention within the fuel element For minimizing purposes Valves fail safe Further mitigation by filtered venting of the reactor building In case of non-isolatable leakages unfiltered release of coolant to environment via stack, no exceeding of limiting values of Art. 28.3 StrSchV. 

As PROFISAFE communication protocol has the built in safety features, all connected devices in PROFIBUS DP and PA, as well as PROFINET, can use the same for safety application. This also facilitates uses of devices in two buses to communicate without the need for any gateway and or bridge. A similar thing has been shown in Fig. VII/2.2.4-1 also. In common CPU with failsafe software, standard and fail-safe I/Os can be connected by common PROFIBUS DP. In application, there shall be two parts one fail-safe which shall communicate with fail-safe I/Os, whereas so-called non-interfering application can be there for standard I/Os as shown in Fig. IX/2.2.3-2. PROFISAFE has TUV Certification to lEC 61,508 SIL 3/EN 954-1 Cat 4. 

The software reqrrirements shoirld be analysed for ambiguities, inconsistencies and undefined conditions deficiencies shonld be identified, clarified and corrected. The software requirements shoirld be verifiable and consistent. The functional requirements should be stated in mathematical terms where possible. Non-fimctional software requirements, such as minimum precision and accnracy, time behavionr, independence of execution threads and fail-safe behavionr, shonld also be stated exphcitly and, whenever required, in quantitative terms. 

Did the loop testing confirm that the alarm/interlock (safety non-safety) action proved, under all conceivable failure conditions, to be fail-safe ... 

Safety integrity level 1 equates to a simple non-redundant single path designed to fail safe with a typical availability of 0.99. Level 2 involves a partially redundant logic structure, with redundant independent paths for elements with lower availability. Overall availability is in the range of 0.999. Level 3 is composed of a totally redundant logic structure. Redundant independent circuits are used for the total interlock system. Diversity is considered an important factor and is used where appropriate. Fault tolerance is enhanced since a single fault of an ESD system component is unlikely to result in a loss of process protection. 

Abstract. The development of mixed-criticahty systems that integrate applications of different criticality levels (safety, security, real-time and non-real time) in a single embedded system can provide multiple benefits such as product cost-size-weight reduction, reliability increase and scalability. However, the integration of applications of different levels of criticality in a single embedded system leads to several challenges with respect to safety certification standards. This research paper describes a safety concept for a fail-safe wind turbine mixed-criticality control system based on multicore partitioning that meets IEC-61508 and ISO-13849 industrial safety standards. The safety concept has been positively assessed by a certification body. 

Process safety and operability are checked — for example, orientation of relief valves, fail safe systems, orientation of non-return valves, access to valves and adequate provision of drains and vents. The plant is finally checked for cleanliness, removal of construction debris and so on. 

Piping systems should be designed to be cleaned on-stream, if possible and necessary. Critical parts or parts of systems subject to heavy corrosion should be separately dismantleable. Blind or non-inspectable areas should be kept to a minimum in a fail-safe design and, where unavoidable, additional strength must be provided to prevent the critical effects of corrosion fatigue. 

The PSS system has been designed to allow standard (or basic ) control functions to be performed as well as safety related control functions. Safety functions are known as FS and standard are called ST. FS software runs in all three processors using an FS working bus. A separate bus is provided for the A processor to perform ST instructions. The dual function structure of the PSS has fail-safe controls operating with an independent triple voting bus whilst standard or non-safety functions operate only in processor A on a separate working bus. 

Safe using of the various lifting machines like cranes, mine hoists, air rope ways, elevators etc. depends on steel wire ropes durability. Ropes are non repairable components of the machines. That is why the ropes worn or failed must be changed. 

Electroconvulsive therapy (ECT) is a highly efficacious treatment for MDD. The response rate is about 80% to 90% and even exceeds 50% for patients who have failed pharmacotherapy.16,17 ECT may be particularly beneficial for MDD that is complicated by psychotic features, severe suicidality, refusal to eat, pregnancy, or contraindication/non-response to pharmacotherapy.16,17 ECT is typically a very safe treatment alternative, but various cautions do exist, and the chief side effects are confusion and memory impairment.16... 

Treat conditions that cause bothersome maternal symptoms during pregnancy with drug therapy only after non-pharmacologic methods fail. Choose therapy with the longest history of safe use in pregnancy. 

Second hand marijuana smoke in a car can cause you to fail the next day (Nightbyrd). It is possible that second hand [marijuana] smoke will raise someone to the 50 ng/mL level however, extreme exposure is required. For instance, a closed car full of pot smokers and a non-smoker may render the non-smoker positive for both urinalysis and the hair test, provided that they are sealed in the car for a while. The Army did a case study where volunteers were put in a room pumped full of smoke for an hour, five times daily. Subjects started testing positive after the second day. The non-smoker would have to take in virtually as much second hand smoke as a smoker inhales. Non-smokers are safe in a ventilated area, as long as they don t get a hair test. According to Clinton, simply blowing crack smoke on ones hair may cause a positive hair test. Second hand pot smoke doesn t affect the hair test results as much as crack smoke does mainly because exhaled smoke contains no THC. The only pot smoke that contains THC is the smoke that hasn t entered the lungs. 

In another study the acute response to inhaled nitric oxide and high doses of oral nifedipine or verapamil was assessed in 33 consecutive patients with primary pulmonary hypertension (2). Ten patients responded acutely to nitric oxide, nine of whom responded acutely to calcium channel blockers, without any complications. The other 23 patients failed to respond to nitric oxide and calcium channel blockers. In these non-responders there were nine serious adverse effects with calcium channel blockers. There was no clinical or baseline hemodynamic feature that predicted the acute vasodilator response. Long-term oral treatment with calcium channel blockers was restricted to the nine acute responders, and there was a sustained clinical and hemodynamic improvement in only six patients. It was concluded that nitric oxide may be used as a screening agent for safely identifying patients with primary pulmonary hypertension who may benefit from long-term treatment with calcium channel blockers. 

Thyroid hormones are used either to replace the failing function of the thyroid gland (spontaneous or drug-induced) or to suppress the endocrine function of abnormal thyroid tissues (especially non-toxic struma or goiter or after thyroidectomy for thyroid neoplasms). Although there are abnormalities of the peripheral metabolism of thyroid hormones in some forms of undernutrition or overnutrition, thyroid drug therapy cannot be considered a safe way of treating obesity. 

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