Alarm system

In the examples given above, we see how important an early intervention is in case of runaway. Whatever the measure considered, the sooner it becomes active the better. An exothermal reaction is obviously easier to control at its beginning, before the heat release rate becomes too great. This is true for emergency cooling as well as for controlled depressurization. Thus, the idea arose to detect a runaway situation by an alarm system. The first attempt in this direction stems from Hub [15, 16], who proposed evaluating the second time derivatives of the reactor temperature and the first derivative of the temperature difference between reactor and jacket, giving a criteria for a mnaway  

One important difficulty is that the noise of the temperature signal in the industrial environment is amplified by the derivation, which is at the cost of the accuracy of the method. These criteria give an alarm between 20 and 60 minutes before mnaway [16], which is a short time, that is, the runaway is well-developed when the alarm is activated. 

Modern cryogenics plants are well-instrumented to indicate process temperatures and pressures, flow rates, liquid levels, and contaminant concentrations. These instruments are used for measurement, control, and safety if a particular variable (temperature, pressure, flow rate) falls outside the control range, a corrective action is initiated automatically and, if necessary, an alarm may also be actuated. Complete alarm systems are now available commercially for use with all the common safety devices. Further, many are designed on the failsafe principle and sound an alarm in the event a power failure occurs. 

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The accident at the Three Mile Island nuclear plant clearly demonstrated that an alarm system can be counterprociuc tive. An excessive number of alarms can distract the operator s attention from the real problem that needs to be addressed. Alarms that merely tell the operator something that is already known do the same. In fac t, a very good definition of a nuisance alarm is one that informs the operator of a situation of which the operator is already aware. The only problem with applying this definition is determining what the operator already knows. 

Process operators are expected to be exercising normal surveillance of the process. Therefore, alarms are not appropriate for situations known to the operator either through previous alarms or through normal process sui veillance. The sleeping operator problem can Be addressed by far more effective means than tne alarm system. 

Intelligent alarms. Logic is incorporated into the alarm system to determine the nature of the problem and then issue a single alarm to the process operator. Sometimes this is called an expert system. 

Alarm system design should consider which measurements are to be alarmed the number, type, and urgency of alarm type of alarm (i.e., visual/audible) etc. 

The OREDA Offshore Reliability Data Handbooks covers a variety of components used in offshore oil drilling and platforms, including gas/fire detection systems, process alarm systems, firefighting systems, pressure relieving systems, general alarm and communication systems, evacuation systems, process systems (vessels, valves, pumps, heat exchangers, and compressors), electrical and utility systems, and drilling equipment. 

Direct expansion is also possible wherein the refrigerant is used to chill the incoming air directly without the chilled water circuit. Ammonia, which is an excellent refrigerant, is used in this sort of application. Special alarm systems would have to be utilized to detect the loss of the refrigerant into the combustion air and to shut down and evacuate the refrigeration system. 

In addition, the new eontrol systems inerease turbine performanee, while speed eontrol and flexibility are greatly improved. The original design has been supplemented to inelude a self-eontained alarm system, a semi-automatie sequential start system, and a eomplete trip and proteetion system, as well as the eleetronie eontrols. The eost of this system is substantially less than the eost of a similar deviee offered by the OEM on new maehines. 

A eombination of deteetors may be appropriate. They may aetivate an alarm only, or aetuate a eombined alarm/extinguishment system. With a bank of deteetors a voting system may be used to inerease reliability and reduee the frequeney of spurious alarms. Deteetion/alarm systems may also be interlinked with, e.g., fire-eheek doors held baek on eleetromagnetie eatehes sueh that the doors elose automatieally upon aetivation of the deteetion system. 

Consider die need for deteedon/alarm systems and in any event eheek periodieally for leaks with e.g. soap soludon, never with a naked flame. 

Work in well-ventilated area wearing appropriate skin proteetion and respiratory equipment. Cheek for leaks (e.g. witli aqueous ammonia) and eonsider the need for deteetion/alarm systems. Leaks should be dealt with immediately after evaeuating the area. 

The integrity of pipelines depends upon conect design, including materials selection, support and protection from mechanical damage. Depending upon tlie gas, routine inspection and maintenance may be supplemented by the provision of gas detection and alarm systems. Other considerations are exemplified by the safety-related controls on the transportation of domestic gas via pipeline systems summarized in Table 15.17. 

AMD 1 Portable fire extinguishers. Provisions for the attestation of conformity of portable fire extinguishers m accordance with EN 3 Parts 1 to 5 (AMD 10494) dated September 1999. With BS EN 3-1 to 5 and BS 7863 1996, superseded BS 5423 1987 Eire detection and fire alarm systems. Introduction, supersedes BS 5445 Part 1 1977... 

Fire detection and fire alarm systems. Control and indicating equipment. With BS EN 54-4 1997, superseded BS 5839 Part 4 1998 which remains cuiTcnt... 

In eontrast, emergeney evaeuation proeedures had not been rehearsed at Sites E and K, and some employees at the Site K expressed doubt that the employee alarm system (portable air horns) would be audible above site noise levels or would be aeeessible for all emergeneies. 

Employers, at a minimum, must have an emergency action plan that will facilitate the prompt evacuation of employees when there is an unwanted release of a highly hazardous chemical. This means that the employer s plan will be activated by an alarm system to alert employees when to evacuate, and that employees who are physically impaired will have the necessary support and assistance to get them to a safe zone. The intent of these requirements is to alert and move employees quickly to a safe zone. The use of process control centers or buildings as safe areas is discouraged. Recent catastrophes indicate that lives are lost in these structures because of their location and because they are not necessarily designed to withstand over-pressures from shock waves resulting from explosions in the process area. 

EMERGENCY RESPONSE 1910.120(b)(4)(iii)(h), SAEETY AND HEALTH PROGRAM 1910.120(e)(7), TRAINING, EMERGENCY RESPONSE 1910.120(1), EMERGENCY RESPONSE 1910.165, EMPLOYEE ALARM SYSTEMS... 

Does the SAHP deseribe an emergeney response alarm system If so ... 

Does the alarm system provide positive notifieation whenever a defieieney exists in the system [OSHA Referenee... 

Since process disturbances do take place, and accidental releases are possible, even from processes closed under normal conditions, the plants where highly toxic or sensitizing substances are in use or may be generated should be provided with continuous monitoring and alarm systems in the critical areas. 

Provide alarm systems to warn of malfunctions in the environment. 

In cold weather, the trace heating on instruments that form part of trip and alarm systems should be inspected regularly. This can be part of the test routine, but more frequent testing may be necessary. 

Activation level install alarm system for indicating valve left open. Observation level provide checklist to operators make valve more accessible or remotely operable. 

At B, develop an alarm system indicating when a wrong connection is made... 

Design of human-machine interfaces (e.g., process information displays, alarm systems, plant labeling)... 

The plan must include a list of all emergency equipment at tlic facility (such as fire cxtinguisliing systems, spill control equipment, internal and c.xtcrnal communications and alarm systems, and decontamination equipment). In addition, the plan must include for each item on the list a physical description, a brief outline of its capabilities, and its location... 

A means of notification of tlie public by an alarm system... 

Too much o.xygen Runaway reaction/ Alarm system/feed... 

The type of alarm system used is dependent on the expected type of security breach and the method employed in responding to one. In unguarded premises, requiring only a low level of security, an alarm that operates immediately a device detects a security breach may be sufficient to ward off vandals, burglars and crimes of opportunity. On the other hand, where breaches of security may involve more determined criminals, such as fraud or industrial espionage, delayed alarms on the premises may give time for security personnel and/or police to apprehend the criminal in the process of committing the crime. 

No alarm system, however well planned and installed, can be completely reliable or tamperproof. The successful operation of a security system requires the active cooperation of those involved in carrying out the necessary procedures carefully and thoroughly. The usefulness of the whole system can be jeopardized by lack of care or inadequate attention to routine procedures in maintenance and servicing. This care has to be extended to the security of keys and of information regarding the system, its installation and method of operation. 

An important principle is that security must be built in depth - otherwise known as defense in depth. In this context, it may be helpful to think of security as a set of concentric rings, where the target is located at the center. Each ring represents a level of physical protection (perimeter fence, building shell, security case) but the number of rings and security resistance will vary relative to the risk. The spaces between the rings may represent other defensive measures such as closed-circuit television (CCTV), security lighting, intruder alarm systems, etc. 

In many cases, it is necessary to complement physical security by the installation of an intruder alarm system in order to achieve the standard of security commensurate to the risk exposure. The scope of protection to be afforded by the alarm system depends on the security risk, but it may embrace fences, windows, doors, roofs, walls, internal areas, yards and external open areas, and vehicles inside and outside buildings. There is a comprehensive range of detection devices, but the choice of detector is critical to ensure that it provides the desired level of protection and is stable in the particular environment. 

Intruder alarms are designed to give a warning of the presence of an intruder within or attempting to enter the protected area. Alarm systems may act as a deterrent to the casual or opportunist thief but they will do little or nothing to prevent a determined intrusion, and to be effective they must provoke an early response from the appropriate authority (in most cases the police). The warning may be a local audible device, but normally the alarm signal is transmitted by the telephone network to a central station operated by a security company on a 24-hour basis. 

A number of alarm systems suffer from repeated false alarms. This may be due to the poor design and selection of detectors, inadequate standards of installation or preventative maintenance, and faulty operation of the system by key holders. Recurrent false calls will quickly discredit any system and may result in the withdrawal of police response to any alarm activation. 

While alarm systems may be complex, false alarms can be minimized by the careful choice of installer, who should ... 

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