Interrupts, alarm

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. 

Various types of detectors that recognize heat and/or smoke utilizing fused bimetallic strips, ionization chambers and the interruption of a light beam by smoke or other combustion products. It is important to select the most appropriate form of detector for the environment. Insurers give a modest discount from premiums if the alarm installation complies with the insurance rules. 

An alarm system should be provided to warn workers of power interruptions that have occurred during non-duty hours. Such evidence that engineering controls have been compromised alerts incoming personnel to the necessity for first entry monitoring of laboratory rooms. 

These are actions of the computer which are initiated by events, e.g. switching off a pump when a tank has been filled to a certain level. They form the basis of the response of computer-controlled plant to alarm conditions, e.g. if the temperature in the reactor described in Fig. 7.102 exceeds a specified value then action must be taken by the computer, such as rapidly increasing the flow of coolant or reducing the feed to the reactor. Generally, sensor-initiated operations must be performed within a specified maximum time interval and are often in the form of alarm interrupts (Section 7.18.3). Smaller systems will regularly scan a set of specific process variables via a multiplexer to see if any action is necessary. The latter arrangement is called polling. 

Am), which sends a stream of radiation to a detector. The smoke alarm goes off when this stream is interrupted by smoke—or steam, which is why smoke detectors in the kitchen can have an annoying habit of going off even when there isn t a fire. But smoke detectors have saved an impressive number of lives, so resist the temptation to disable the annoying smoke detector and provide the kitchen with better ventilation instead. 

One application of photocells is in motion detectors for security alarm systems. A beam of light is emitted by a special device so that it strikes the photocell precisely, producing a tiny electric current. If something or someone breaks (interrupts) the beam, the current stops flowing and an alarm sounds. 

Should an emergency occur requiring immediate shutdown and over-ride of normal sequenhal shutdown, an EMERGENCY STOP pushbutton is provided for this purpose. This device interrupts power to all components in the oxidation unit control circuit, shuts down all motors, and closes the vacuum line valve and the chlorine pressure-reducing valve (PRV). The EMERGENCY STOP pushbutton is also used as a reset device to restore the system to normal operating status after an alarm situation has occurred. 

An audible and/or visible alarm is recommended in the safety circuit to give warning of unsafe conditions or interruption of the safety circuit. 

A weak radioactive source such as americium is used in some smoke detectors. Radiation from the source ionizes the air to produce a weak current. Smoke particles interrupt the current flow by attracting the ions. This decrease in current triggers the alarm. 

Commercial power disrupted and TOCDF changed to emergency backup power. ACAMS alarmed in the DFS due to the interruption of the airflow. As a precaution TOCDF suspended munition processing and RTAPS deployed with negative readings. Demil process resumed after commercial power restored. 

In April 1989, a routine preliminary review of the study by the Safety and Monitoring Board revealed alarming results, and the study was interrupted. The results showed that compared with placebo, treatment with encainide or flecainide was associated with a significantly... 

A smoke detector is a device that sounds an alarm in the presence of smoke particles from a smoldering or burning object. An ionizing smoke detector, like the one illustrated here, contains an electrical sensor that detects smoke particles that interrupt an electrical current. Ionizing detectors usually contain the unstable isotope americium-241 ( IgAm), which decays to form 93 Np and fHe. 

In many situations, the most likely scenario for failure of freezers is power interruption. In this case, the temperature monitoring and alarm systems need to function in the absence of power. In some settings, generator back-up is appropriate and required. Several types of temperature monitors are available, including those that record continuously on paper discs and recorders that electronically record, store, and alarm in case temperature parameters are exceeded. 

Cesium 137 is an artificial radionuclide used in clinical, industrial, and research applications and one of the main radioactive products of fission reactions taking place in nuclear reactors. The possibility that the anomalous radioactivity derived from active nuclear plants can be rule out as the i Cs was not accompanied by the other radionuclides produced during fission. Towards the end of April 1998, an incident occurred at the Algeciras steel works in southern Spain with emissions of Cs coming from a radioactive source no longer in use. This source ended up in the foundry. The fact that the presence of Cs was interrupted for a week and then resumed is not unusual as the transport and soil deposition of air-dispersed pollutants is strictly linked to wind and precipitation. The levels of radioactivity were negligible and many times below every alarm threshold, but the bee matrix promptly revealed the presence, albeit minimal, of Cs... 

Modern communications are much more transaction based (a trend developed in the commercial and business sector), and these are less suited to traditional control system interfaces. Control systems have traditionally operated on a real-time basis, polling for data on a routine basis or being interrupt driven by alarms and events. These traditional systems are not well suited to transactional-based communications, and the use of object broker interfaces will overcome some of these problems. The new object-oriented interfaces will again be easier to validate since the object broker interfaces will be configured rather than programmed and will use standard software blocks to build the interfaces. 

The pipeline is assumed to be highly reliable. In certain intervals, however, the pipeline control system reports failures which are partly caused by misestimations of pressure but sometimes also due to micro-leakages. In any case, an inspection of the identified pipeline segment is necessary which forces an interruption of pipeline operations. It is assumed that the time span between two alarms (given in days) is Weibull distributed with... 

Safety-related information should be distinguished from non-safety-related information and highlighted. In addition, when safety interlocks are being overridden, their status should be displayed. Similarly, if safety-related alarms are temporarily inhibited, which may be reasonable to allow so that the operator can deal with the problem without being continually interrupted by additional alarms, the inhibit status should be shown on the display. Make warning displays brief and simple. 

NO or NOT No flow Pump P2A fails No supply of coolant to the process pressure alarm via PAL06, PSL07 interrupts supply of one of the feed materials Activation of reserve pump P2B... 

According to the operating manual valve V has to be closed whenever a stronger than usual smell of ammonia is perceived. This is a safety-geared measure. A conflict of interests is not possible because the production is not affected by a temporary interruption of ammonia flow to the pressurized storage, which in turn supplies the production process. The pressurized storage contains sufficient ammonia for several days of operation. For this reason closing the valve because of a false alarm would not be problematic. 

Case study 11.1 Overhlling of a petrol tank with subsequent fire and explosion A tank for petrol is filled with a mass flow rate of about 120 kg/s. Filling takes place 13 times per year [6]. In order to avoid possible overfilling and a release of petrol to the environment a level alarm high (LAH) is installed. On hearing the alarm the operator should activate a pushbutton switch which stops the pump and closes the shutoff valve by interrupting the electric supply. The motor stops and the... 

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