Alarms supervision

Operator control stations. These typically consist of color graphics monitors with special keyboards, in addition to a conventional alphanumeric keyboard, containing keys to perform dedicated functions. Operators may supervise and control processes from these stations. A control station may contain a number of printers for alarm logging, report printing, or hard-copying process graphics. 

Control and supervision systems should be designed with circuit monitoring and self-diagnostic testing to verify that the field sensors and devices are electrically active and connected. The system should alarm when an electrical fault is detected. 

Care should also be taken in the use of recovery factors, because these can exert a significant effect. In general, recovery paths are appropriate where there is a specific mechanism to aid error recovery, that is an alarm, a supervising check, or a routine walk round inspection. 

The IR detectors are usually connected to a controller that supplies power to the detectors and acts as a signal processor and output device. A typical controller monitors up to four detectors and energizes an output when any one of the detectors senses IR radiation that exceeds the alarm threshold level. The controller also contains the circuitry that checks the detectors and electrically supervises the interconnecting wiring to the explosive squibs or solenoid valves by trickling a small current through the external circuits. 

Basic Controls, Process Alarms, and Operator Supervision (BPCS). Continuously during operations and emergencies. None ... 

The detection and alarm circuits of fire and gas detection systems should be continuously supervised to determine if the system is operable. Normal mechanisms provide for a limited current flow through the circuits for normal operation. During alarm conditions current flow is increased while during failure modes the current level is nonexistence. By measuring levels at a control point the health of the circuit or monitoring devices can be continuously determined. End-of-line-resistors (EOLR) are commonly provided in each circuit to provide supervisory signal levels to the control location. 

In NO loops or circuits, all of the system s sensors and switches are connected in parallel. The contacts are at rest in the open (off) position, and no current passes through the system. However, when an event triggers the sensor, the loop is closed. This allows current to flow through the loop, powering the alarm. NO systems are not supervised because the alarm will not be activated if the loop or circuit is broken or cut. However, adding an end-of-line resistor to an NO loop will cause the system to alarm if tampering is detected. 

The type of fire alarm system should be chosen based on personnel resources available at the facility. For continuously staffed facilities, proprietary supervised systems are preferred. For facilities staffed less than continuously, remote supervised station or central station fire alarms system are usually considered. In these systems, alarms are monitored by an outside firm responsible for alerting appropriate personnel or by the local fire department. 

Power for the control panel should be provided with a suitable uninterrupted power supply (UPS). The panel will provide a DC current to field detectors. This power will enable the panel to monitor all input circuits, output circuits, and trouble signals within the detectors, such as shorts, ground faults, and detector disconnects. It will also provide an AC powering signal to field output devices. All output circuits should be similarly supervised for trouble. An example alarm and detection control panel is shown in Figure 7-18. 

Fig. 10. Determining test interval for critical instruments. Example of tanker off loading which is operator supervised. The tank has a local level indicator (LI) and separate level alarm (LA) and level switch (LSW). Offloading is performed 10 times per year, (x) is the number of operations per year. Probability of overfill equals l(T4(x). Proposed target is less than or equal to 3 x 10 5. Testing interval 10-4(x) < 3 xl0 5(x) 3 x 10 1 = 4 months. Note that if only one tanker is offloaded per year, it is better to check LSW prior to offloading.

Workstations. Workstations are the most powerful computers in the system, capable of performing functions not normally available in other units. A workstation acts both as an arbitrator unit to route internodal communications and as the database server. An operator interface is supported, and various peripheral devices are coordinated through the workstations. Computationally intensive tasks, such as real-time optimization or model predictive control, are implemented in a workstation. Operators supervise and control processes from these workstations. Operator stations may be connected directly to printers for alarm logging, printing reports, or process graphics. 

Required Annual testing of alarm (or every two months if not a supervised system)... 

There should be one or more senior operatives who are knowledgeable and well trained in precautionary and protective measures and also compliance with pesticide regulations. They should be responsible for the day-to-day supervision of plant operations, applications in the field, etc. No person should work alone while handling or likely to be exposed to anti-ChEs. There should always be an additional person nearby, designated as safety officer, who can view the operation at a distance sufficient, if necessary, to raise an alarm, to allow protective clothing and equipment CO be donned, and to undertake the initial rescue and possible first aid and resuscitation measures. Thus, ideally this person should be trained in the emergency mea.sures for an anti-ChE leak, spill, and exposure, and it is desirable for him or her to be trained in first aid measures to treat OP and CM poisoning. 

Fire protection is provided in the HCF. B6580 and B6581 are provided with automatic fire-protection sprinkler systems, except in areas containing significant quantities of radiological materials where water sprinklers would exacerbate radiological hazards. The building also has a fully supervised alarm and evacuation system, which includes automatic smoke and heat detectors in certain areas. 

With regard to normal and abnormal states of hazardous plant several monitoring and control loops may be distinguished as illustrated in Fig. 3. In normal plant states and some disturbances the operator is supervising the technological process because the control is performed automatically. In case of malfunctions and abnormal states the operator should be informed about current situation by the alarm system. The role of operator in hazardous state of the plant (dashed line), in order to prevent a serious accident, can be decomposed into several general task illustrated on Fig. 4 (Hollnagel 2005). 

Ensure all systems meet NFPA standards and local requirements. All manually operated fire systems must be electrically supervised. The system must also automatically transmit an alarm to the fire department. Notify the local fire department by other means when the ALARM HAS BEEN ACTIVATED (Tables 9.6 and 9.7). 

Packaged units have traditionally had their own progranunable logic controllers (PLCs) and local control panels. This is especially true in the case of units that require extensive sequence controls for stepwise processes such as filtration and ion exchange. Many operators find it more convenient to have control supervised from a central station. From this point of view, these systems are better controlled by a distributed control system (DCS) and monitored from the control room. Some who bought systems equipped with PLCs some years ago have dispensed with the PLCs and moved control to the DCS. Many favor systems which combine local control by PLC with status and alarm signals sent to the DCS. 

Today s stationary infusion pumps are highly sophisticated electromechanical devices that allow the user to program the desired flow rate and infusion volume for one or more i.v. lines. They are equipped with several alarm features to indicate potentially hazardous conditions such as changes in the flow rate, air in the hne, or occlusion of the catheter. The pump mechanism is either a peristaltic compression and release of the administration line or motor-controlled piston movement. The price of these devices ranges from 2,000 to 8,000, which excludes the disposable i.v. sets. The majority of these pumps are used in a hospital setting, where they are operated and supervised during operation by the medical staff. Health-care providers also lease stationary infosion pumps to chronically ill patients for home use. A flow-rate accuracy of 3 10% makes these pumps highly desirable for administration of proteins with a narrow therapeutic-index. 

In general, the strategy for reducing risk could involve reducing the frequency of either the risk or the consequence of the potential accidents. The frequency of the risk could be reduced by having several layers of safety checks or controls (see Fig. 8.1). A process could have a slave and a master controller, followed by a set of alarms, and, finally, manual supervision. In such a design, an uncontrolled event would arise only if all the controls and checks failed. If the probability of such failure of each of the event is about 0.02 (i.e., 2%), then the probability of a hazard to occur would be equal to O.oi = 0.00000016. 

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