Backup Protection

The interrupting device, which may be a breaker or a contactor, must be suitable to sustain this energy w ithoiit deterioration of or damage to its contacts, while the fuses must stay intact when provided for backup protection. 

Established Phillips corporate safety procedures and standard industry practice require backup protection in the form of a double valve or blind flange insert whenever a process... 

Soluable poisons for secondary protection. Generally satisfied for LMFBR fuel compositions by Hanford data, for water-reactor fuel by Y-12 program, if limited to backup protection. But see item 3. 

Line sectionalizer An overcurrent protection device that interrupts the line flow. Used with backup protection devices. 

The dorm was not fitted with sprinklers, nor was it properly compartmentalized, but it had an automatic detection and alarm system that was supposed to ensure the alerting of occupants for moving them outside to safety. However, the fire protection professionals had not planned on many of the students not awakening or just plain ignoring the alarm and not taking action. With the lack of sufficient backup protection in the dorm, the fire quickly spread from the lobby area to the residential areas causing the injuries and deaths. Had the dorms been properly compartmentalized, the spread of the fire would have been slowed considerably, allowing more time for the fire department to arrive and control the fire and for the students to be rescued. 

V Backup protection against system faults Voltage controlled or voltage-restrained time overcurrent relay... 

Backup protection against system faults Distance relay... 

Figure 13.1 The system, with and without backup protection.

Parylene s use in the medical field is linked to electronics. Certain pacemaker manufacturers use it as a protective conformal coating on pacemaker circuitry (69). The coated circuitry is sealed in a metal can, so that the parylene coating serves only as a backup should the primary barrier leak. There is also interest in its use as an electrode insulation in the fabrication of miniature electrodes for long-term implantation to record or to stimulate neurons in the central or peripheral nervous system, as the "front end" of experimental neural prostheses (70). One report describes the 3-yr survival of functioning parylene-coated electrodes in the brain of a monkey (71). 

The hardware and software used to implement LIMS systems must be vahdated. Computers and networks need to be examined for potential impact of component failure on LIMS data. Security concerns regarding control of access to LIMS information must be addressed. Software, operating systems, and database management systems used in the implementation of LIMS systems must be vahdated to protect against data cormption and loss. Mechanisms for fault-tolerant operation and LIMS data backup and restoration should be documented and tested. One approach to vahdation of LIMS hardware and software is to choose vendors whose products are precertified however, the ultimate responsibihty for vahdation remains with the user. Vahdating the LIMS system s operation involves a substantial amount of work, and an adequate vahdation infrastmcture is a prerequisite for the constmction of a dependable and flexible LIMS system. 

Although digital control technology was first apphed to process control in 1959, the total dependence of the early centralized architectures on a single computer for all control and operator interface functions resulted in complex systems with dubious rehability. Adding a second processor increased both the complexity and the cost. Consequently, many installations provided analog backup systems to protect against a computer malfunction. 

A breaker, usually an MCCB or an MCB on an LT system, can be provided with backup HRC fuses to enhance their short-time rating. This may be done when the available MCCBs or MCBs possess a lower short-time rating than the fault level of the circuit they are required to protect, and make them suitable for the fault level of the circuit. But this is not a preferred practice and is seldom used. As a rule of thumb, the device that is protecting must be suitable to withstand electrically and endure mechanically the system fault current for a duration of one or three seconds, according to the system design. 

Now let us consider utility failure as a cause of overpressure. Failure of the utility supphes (e.g., electric power, cooling water, steam, instrument air or instrument power, or fuel) to refinery plant facihties wiU in many instances result in emergency conditions with potential for overpressuring equipment. Although utility supply systems are designed for reliability by the appropriate selection of multiple generation and distribution systems, spare equipment, backup systems, etc., the possibility of failure still remains. Possible failure mechanisms of each utility must, therefore, be examined and evaluated to determine the associated requirements for overpressure protection. The basic rules for these considerations are as follows ... 

It is not always practical to duplicate eveiy element of the protection chain. Particularly on lower voltage systems, backup relaying is used. Backup relays are slower than the primary relays and, generally, remove more system elements than may be necessary to clear a fault. They may be installed locally, that is, in the same substation as the primary relays, or remotely. 

This accident was attributed to the lack of design protection to prevent the backup of ammonia into this storage tank. It also appears that mitigation techniques were not part of the system (deluge systems, dikes, and the like). 

Several catastrophic fire incidents in the petroleum industry have been the result of the facility firewater pumps being directly affected by the initial effects of the incident. The cause of these impacts has been mainly due to the siting of the fire pumps in vulnerable locations without adequate protection measures from the probable incident and the unavailability or provision of other backup water sources. A single point failure analysis of firewater distribution systems is an effective analysis that can be performed to identify where design deficiencies may exist. For all high risk locations, fire water supplies should be available from several remotely located sources that are totally independent of each and utility systems which are required for support. 

Fire pumps should be solely dedicated to fire protection. They may be used to feed into a backup system for emergency process cooling but not as the primary supply. If such backup is allowed is should be tightly controlled and easily accessible for prompt shutdown in case of a real emergency. 

Hydrants should be considered as a backup water supply source to monitors and fixed fire suppression systems. Hydrants should be located on the ring main at intervals to suitably direct water on the fire hazard with a fire hose. Hydrants monitors and hose reels should be placed a minimum of 15 meters (50 ft.) from the hazard they protect for onshore facilities. Hydrants in process areas should be located so that any portion of a process unit can be reached from at least two opposite directions with the use of 76 meters (250 ft), hose lines if the approach is made from the upwind side of the fire. Offshore hydrants are located at the main accessways at the edge of the platform for each module. Normal access into a location should not be impeded by the placement of monitors or hydrants. This is especially important for heavy crane access during maintenance and turnaround activities. 

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