Interlocks Trips

What-if interlocks, trips, and shutdowns fails What-if gas detection for flammables or toxics fail ... 

To ignore the existing system, identify the cause and consequence of the hazard, and then apply the safeguard such as an alarm, interlock trip, etc. In this method there is very little chance that anything is missed. 

INPUT, INTERLOCKING, TRIP AND EMERGENCY STOP DEVICES... 

Does everyone know what is still energized after the interlock trips ... 

Zone 1 doors interlock tripped preventing entry into Zone 1. 

For filter boxes, provide remote and automatic filter box lid closing on trip of appropriate fire detection device. Fire detection device may also be interlocked to stop solvent feed, trip deluge internal to filter box and/or trip inert gas blanket for filter box (caution, be aware inert gas is a potential asphyxiation hazard)... 

The electrical interlocking should preferably be provided through shunt trip releases. It must have a separate a.c. or d.c. source of control supply, such that the operation of the scheme is independent of the main source of supply. For the same reason, interlocking through undervoltage (U/V) releases is not recommended as its... 

An interlock is provided through a centrifugal type of pressure switch (PS) to trip the engine in the case of low lube (lubricating) oil pressure during a run. Since during a. start oil pre.s.sure has not built up, a timer, 7 j is introduced to bypass the trip interlock and avoid a false trip. A relay (contactor), d], is used to provide lube oil pressure interlock. 

Although many engineers provide only the minimum adequate vessel design to minimize costs, it is inherently safer to minimize the use of safety interlocks and administrative controls by designing robust equipment. Passive hardware devices can be substituted for active control systems. For example, if the design pressure of the vessel system is higher than the maximum expected pressure, an interlock to trip the system on high pressure or temperatures may be unnecessary. 

A system of trips or interlocks makes the probability that the relief valve will lift very low, say, less than once in 1,000 years for flammable liquids and less than once in 100 years for flammable gases. 

Trips and interlocks should be tested after a major shutdown, especially if any work has been done on them. The following incidents demonstrate the need to test all protective equipment ... 

The view is therefore growing that we should try to design plants so that they are safe even if there is a fault in the software. This can be done by adding on independent safety systems, such as relief valves and hardwired trips and interlocks, or by designing inherently safer plants that remove the hazards instead of controlling them (see Chapter 21). 

In the UK. interlock is used to desciibe a device that prevents someone opening one valve while another is open (or closed). Trip describes an auioniaiic device that closes (or opens) a valve when a temperature, pressure, Jlow. etc., reaches a preset value. 

The shutdown system will have adequate interlocks to prevent inadvertent trips. The system must include two-out-of-three voting or backup instruments. The operators must trust the system for it to remain in service. 

Control of the process. Prevention of hazardous deviations in process variables (pressure, temperature, flow), by provision of automatic control systems, interlocks, alarms, trips together with good operating practices and management. 

When using the operability study technique to vet a process design, the action to be taken to deal with a potential hazard will often be modifications to the control systems and instrumentation the inclusion of additional alarms, trips, or interlocks. If major hazards... 

The reactor protective interface provides signals for protective actions. Examples of protective actions include control rod withdrawal interlocks and startup rate reactor trips. 

Failures can either be fail-safe or fail dangerously. Fail safe incidents may be initiated by spurious trips that may result in accidental shutdown of equipment or processes. Fail dangerously incidents are initiated by undetected process design errors or operations, which disable the safety interlock. The fail dangerously activation may also result in accidental process liquid or gas releases, equipment damage, or fire and explosions. 

The actual test is performed by operating the process to the trip point, and ensuring that the intermediate relays and instruments respond properly. The simulated test is used in circumstances in which the instruments are of a nature that create a forced shutdown or startup in a very hazardous process. The simulated test is also used if the instrument schemes are so complicated that the interlocks cannot be checked on a single-trip shutdown. [26]... 

Are there hardwired trips and interlocks Challenge them. 

Verify correct operation of alarms, trips, and interlocks. 

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