Alarms required types

Note Alarms and shutdowns as shown are not to be considered as meeting any minimum safety requirement but are shown as representative of types used for controi systems. Schematic Alarm/Shutdown Hydrocarbon Low Pressure Hot oil or Glycol Amine Label Description Line Heater Reboiler Steam Heater Salt Heater Reboiler Reboiler ... 

There are few chemical plants that are so forgiving that a control system or a safety interlock system is not required. Process engineers provide controls to assure product yield and quality and maintain safe operating conditions. This type of control system is a BPCS. The BPCS acts to alarm and moderate a high or low operating condition specified by the normal operating limits within the never exceed critical limits. The SIS is provided to shut down or otherwise place the process in a safe state if the BPCS fails to maintain safe operating conditions. A BPCS should not be used as the sole source of a process safety shutdown. 

Elydranlic (liquid seal) flame arresters require attention on a regular basis similar to that for dry-type flame arresters. It is critical to ensnre that the liquid level is at the required height, and level instmmentation with alarms is recommended. Automatic addition of makeup liquid (to replace evaporation and entrainment losses) is desirable. Temperatnre instrumentation is also recommended to monitor the occurrence of sustained burning (a stabilized flame). See Section 5.3.18 for more details. 

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. 

Expertise required to operate One of the objectives for using microprocessor-based predictive maintenance systems is to reduce the expertise required to acquire error-free, useful vibration and process data from a large population of machinery and systems within a plant. The system should not require user input to establish maximum amplitude, measurement bandwidths, filter settings, or allow free-form data input. All of these functions force the user to be a trained analyst and will increase both the cost and time required to routinely acquire data from plant equipment. Many of the microprocessors on the market provide easy, menu-driven measurement routes that lead the user through the process of acquiring accurate data. The ideal system should require a single key input to automatically acquire, analyze, alarm and store all pertinent data from plant equipment. This type of system would enable an unskilled user to quickly and accurately acquire all of the data required for predictive maintenance. 

The second method uses dynamic limits that monitor the rate of change in the measurement parameters. This type of monitoring can detect minor deviations in the rate that a machine or system is degrading and anticipate when an alarm will be reached. The use of dynamic limits will greatly enhance the automatic diagnostic capabilities of a predictive maintenance system and reduce the manual effort required to gain maximum benefits. 

Each type of emergency alarm or signal must clearly inform those onsite of the actions to be taken. This requires training and testing of the alarm so personnel can recognize the alarm and take appropriate action. Some of these alarms may be automatic. For example, detection of a fire may be signaled directly by the protection or detection system rather than by an individual. This alarm signal may alert not only personnel in the immediate area, but all facility personnel and the community fire department. 

Where releases of flammable or toxic chemicals are possible, a flammable or toxic gas alarm system is often established as part of the plant emergency alarm system. Best practices require different types of alarms to be annunciated differently, both audibly and visually. For example, the toxic alarm stations may be provided with a blue light to distinguish them from fire alarm stations that are red. A consistent color system for lights should be adopted. 

Fixed temperature detectors are preferred because they require less calibration and maintenance. Heat detectors are normally more reliable than other types of detectors because of the simple nature of their operation and ease of maintenance. These factors tend to lead to fewer false alarms. The main disadvantage of heat detectors is that they are unlikely to detect fires in the incipient stage, where little heat is generated, but much smoke is likely.. Since heat detectors are inherently slower in operation than other types of detectors, they should be considered for installation in areas where high speed detection is not required. 

The major problem for control based on material states, however, is the quality control culture that requires that parts be accepted based on adherence to a preset cycle within specified limits. Because state-based inferential control systems could theoretically come up with a new cure cycle every time, this sort of specification cannot be used with such systems. Specifications instead have to be in terms of the process plan used for the cure. The satisfactory completion of a certain cure history without alarm states would be assumed to produce an acceptable part. Once the culture was able to accept that difference for autoclave curing, production costs at the U.S. air force s McClellan AFB Logistic Center were substantially reduced [32], This type of specification could also give material review boards a head start on investigations because they would know that a part did not meet specification as well as what sorts of flaws might result from the deviation. The experience at McClellan is that there are fewer parts to review. It is even conceivable that, with improvements to sensors, much of the current postcure nondestructive evaluation used to verily the quality of parts could be incorporated into the process, building quality in rather than inspecting it in after the fact. 

A control strategy hope lly can then be evolved. It is also necessary to determine the ancillary instruments required for process monitoring, and for plant commissioning and start-up. It is worthwhile at the design stage including connections for instruments which may be required in the future. The location (local or a distant control room) and types of recorders must be specified, and the alarms and interlocks that are required. Control does not occur independently in different units, and an overall and integrated approach to the control of the plant is required. 

Occasionally, there may be business pressures or maintenance scheduling problems that would encourage the delay of prooftesting of safety critical alarms and shutdown systems. Such situations can also delay of vessel inspections and safety relief valve testing. Some type of variance procedure or review policy should be defined to handle this occasional need. Such a policy ought to require the review of all of the inspection and test records on the specific equipment involved as well as an approval of the superintendent of the area. 

There are two aspects to emergency communications the actual equipment used to communicate information about the incident and the types of communications or information-sharing required. The RCRA has specific requirements for the types of emergency communication equipment (alarm systems, phone or radio communications) that must be present. Under the EPCRA, facilities must provide information about their operations and substances used or stored on site when the Local Emergency Planning Committee (LEPC) or State Emergency Response Commission (SERC) requests it. If the facility uses or stores extremely hazardous substances (EHSs) in reportable quantities, it must appoint a representative to the LEPC. Several laws require that a copy of the ERP be made available to employees and... 

The pyroelectric response of ferroelectrics may be exploited to detect tem-peratnre changes with extremely high sensitivity. The most common devices are nncooled infrared (IR) detectors, which may be used for spectroscopic analysis as well as imaging apphcations. Pyroelectric thin films based on perovskite-type complex oxides, including Pb(Sc,Ta)03 have been deposited by CSD for intruder alarms, gas sensors, and IR cameras. It is anticipated that these thin-film devices will be substantially less expensive to manufacture than existing bulk polycrystaUine devices, which require labor-intensive manufacturing procedures. 

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