Emergency block valves

The name of the material contained in the pipelines should be placed on all lines at the point where they enter or leave the block and at road crossings. Block limit valves and emergency block valves should be painted yellow. 

Other guidelines cited in Reference 5 suggest methods for estimating additional release factors such as release duration or inventories. It should be noted that the above methods are again only approximations. Site-specific designs and process conditions should be evaluated. For example, some facilities may have few, if any, emergency block valves available to isolate a release. Other facilities may be designed for rapid isolation. 

The storage system has remotely operated emergency block valves on all transfer lines into and out of the tank. The storage area has the required drainage to direct a spill away from the tank. Backflow protection has been installed and is tested to prevent backflow into the transfer line and storage. 

I a) A redundant temperature measurement with an emergency block valve (controlled... 

It should be possible to easily isolate fluids in equipment and piping when potentially dangerous situations occur. This can be done using emergency block valves (EBVs). An EBV is a manually or remotely actuated protective device that should be used to provide manual or remote shutoff of uncontrolled gas or liquid flow releases. EBVs can be used to isolate a vessel or other equipment, or an entire unit operation. Manual valves are often used on piping at block limits where it is unlikely that there would be a hazard to personnel if an accident occurs. Remotely controlled EBVs are recommended on tanks and on piping in areas where it may be hazardous for personnel in the case of an accident, or where a quick response may be necessary. 

It should be possible to easily isolate fluids in equipment and piping when potentially dangerous situations occur. This can be done using emergency block valves (EBVs). An EBV is a manual or remotely-actuated protective device that should be used to provide manual or remote shut-off of... 

Fig. 8. Polyethylene tubing on fail-safe, spring-loaded, fire-safe valve used as an emergency block valve.

Additionally, monitoring software which proves that the safe state of the valve is reached each time the valve is operated (once per batch, typically every 8 hours) is written. In case of a test failure or if more than 168 hours have elapsed since the last test, the logic solver output stays in the safe state (emergency block valve closed) and the condition is alarmed. This automatic test allows setting the proof test interval in the PFD calculation to 168 hours. 

Safety instrumented systems (SISs) should be completely separate from the normal control system. AU elements in the safety loop (measurement devices, logic systems, and actuators) must be highly reliable. This alarm system protects the facility against major catastrophes and will often take corrective actions to safely shutdown and isolate a piece of equipment or a facility, using emergency shutdown (ESD) systems that activate emergency block valves and emergency isolation valves. 

Block valves Automated block valves should be placed to stop and/or control flows during emergencies. Ability to transfer hazardous materials from one area to another should be considered. 

Provide hand-operated or automatic block valves, or equivalent valves, for emergency shutdowns. 

Each of these steps might be performed either by direct action of operations or emergency response personnel or by automatic systems. An example of the latter might be an array of toxic or flammable gas detectors that might trip an emergency shutdown system that closes remotely actuated block valves and vents off the process pressure to a flare if two adjacent sensors read above a predetermined vapor concentration. 

Isolation or emergency shutdown (ESD) valves should be installed to stop fuel flow and the process feed flow into the heater in the event of heater tube rupture. These valves can be automatically actuated by controls or safety interlocks or can be manually operated remotely. Remote actuation can be from a control room console or in the field field actuation stations should be located at least 50 ft (15 m) from the heater. It is also common to provide a manual block valve, located at least 50 ft (15 m) from the heater, on each of the fuel and process feed lines. These should be accessible to operators in the event of an incident involving the heater. 

Relief devices Emergencies Process isolation Instruments Adequacy, vent size, discharge, drain and support Dump, drown, inhibit and dilute Block valves, fire-valves and purging Air quality, time lag, reset wind-up and materials of construction... 

However, the records show that the temperature reached 285°F. Moreover, one of the emergency procedures of the plant says that a temperature of 200°F indicates that the relief valve is open. Another procedure requires the closure of the block valve when the temperature exceeds 130°F. 

Generic Safety Issue (GSI) II.G.l in NUREG-0737 (Reference 1), addresses the reliability of the emergency power source which is used for the pressurizer relief (PORVs) and block valves and for the pressurizer level indication in the event of loss-of-offsite power. 

The normal source of makeup water to the K-, L-, and P-Reactor Disassembly Badns is from the filtered water system throu two makeup water fines. One of the fines supplies the MB, while the other supplies the VTS badn (Ref 8-28). Inhered water to eadi badn is supplied through a manual blodc valve and then to a pneumatically operated butterfty valve. The water then flows into the respective section of the Disassembly Bam Filter water can be automatically controlled, but is not usually operated in this manner. Makeiq> water addition is normally manually controlled via the manual block valves. The emergency cooling water pump suction header CW-39 and the river water header RW-1 were once alternative sources of mak water to these Disassmbly Basins. Each of these alternate sources of water have been drained and isolated from the Disassembly Basins (Ref 8-27), and are not considered as sources. 

B.G. Liptak, Instrument Engineers Handbook Process Control, Chapter 6.10 Emergency partial Stroke testing of block valves A.S. Summers. 

At 4.00 a.m. on 28 March 1979, the main feedwater pumps tripped this in itself was not an unexpected or particularly unusual event, and resulted in an automatic shutdown of the turbine it also caused the emergency feedwater pumps to start up, as they were designed to do. Unknown to the plant operators, however, the block valves on both of the emergency feedwater lines had inadvertently been left closed, so that no water was able to reach the steam generators. 

When a fire occurs, it is assumed that all fluid flow to and from the fire risk area has been stopped. Therefore, flow loads such as control valve failure or incoming feed streams are not additive to the fire load. Credit is not generally given to flow out through normal channels, since they could also be blocked during the fire emergency. 

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