Device fail safe

Numerous technical and human failures allowed gas to release from a salt dome storage facility. Lack of fail safe devices contributed to the explosion of the resulting vapor cloud. 

A more expensive alternative is to use standard AutoAnalyser type systems, based on multichannel peristaltic pumps, to pump samples and reagents and/or diluents at the desired rates to give automatic mixing at the desired ratio. Flame photometric detectors have been used for many years with AutoAnalysers, especially in clinical laboratories. Curiously, in the past, this approach has less often been routinely used in environmental analytical laboratories employing flame spectrometry, perhaps because an attractive feature of flame spectrometry is the speed of response when used conventionally. Over the past few years, however, there has been an increasing tendency towards fully automated, unattended operation of flame spectrometers. This undoubtedly reflects, at least in part, the improvements in safety features in modern instruments, which often incorporate a comprehensive selection of fail-safe devices. It also reflects the impact of microprocessor control systems, which have greatly facilitated automation of periodic recalibration. 

Should a fail-safe device be used, of the type that switches off the power when the cooling water ceases to flow, then the water pressure in that device can be varied by raising or lowering the level of the indicator. 

Note The water pressure at the indicator is always atmospheric, in general the water pressure in the fail-safe device should be higher than atmospheric. A long length of tube pushed down the drain to reduce the risk of floods can lower the pressure in the device and make it ineffective. 

You can copy one character to another with function keys 7 and 8. When you press f7, the current character flashes briefly, then is copied into a buffer. Ultrafont + remembers that character pattern. You can position the cursor where you want to copy the character before pressing f8. The memorized character replaces the character the cursor is resting on. You can also use the buffer as a fail-safe device. Before you begin to edit a character you ve already worked on, press f7 to store it safely away. That way, if you accidentally wipe it out or otherwise garble the character, you can press f8 to bring back your earlier version. 

Barstow, David, Laura Dood, James Glanz, Stephanie Saul, and Ian Urbina. Regulators failed to address risk in oil rig fail-safe device. New York Times, New York Edition, June 21,2010, Page Al. 

Although redundant measurements and equipment such as fail-safe devices and the like are often mandatory, accidents still happen. The 2010 Macondo... 

In the most common design, a fail-passive arrangement reduces the system to its lowest energy level. The system will not operate again until corrective action is taken. Circuit breakers and fuses for protection of electrical devices are examples of this type of fail-safe device. Solenoid valves (see Figure 11-3), such as this one on a steam control valve which is configured fail close shuts off instrument air, are another example. 

Fail-Safe Devices Fail-safe devices are safety devices designed to prevent exposure to hazards. They also prevent injury or damage when a system or machine fails. Examples of fail-safe devices are automatic fire doors, air brakes on truck trailers, a dead-man switch on powered hand tools, and safety cans with a spring-closing lid for flammable liquids. 

Fail-safe devices may be fail-passive, fail-active, or fail-operational. A fail-passive device, such as electrical circuit breakers or fuses, wdl render a system inoperative or de-energized until corrective action is taken. A fail-active device will keep a system energized but in a safe mode until there are corrective actions. A fail-operational device allows a system to function safely, even when the device fails. 

The case ended in a products liability lawsuit against the gas valve manufacturer. Had the manufacturer placed the connector in a small plastic bag and shipped it uninstalled, the connector would have changed from a faU-dangerous device to a fail-safe device. The gas valve would not have worked at aU if someone failed to install it when there was no second safety device. It would have worked properly if either the connector or a second safety device were installed. Warnings with the connector would have prevented connecting both during installation of the gas valve. 

There are many design features that can reduce risks in the use of hoisting apparatus. Not all safety features in cranes are fail-safe devices. Each device has limitations. This discussion covers a few examples. 

PROFISAFE is an extended version of the standard PROFIBUS/PROFINET communication protocol. PROFISAFE is a application layer (profile) that describes the communications between fail-safe devices and addresses special requirements in application layer, for safety-related information necessary to conform to strict safety standards. 

If the hazard cannot be designed out, because it is either impossible or cost-prohibitive, then the next best solution is to use fail-safe devices. An example is a valve that fails in a safe manner. In many chanical processes, it is CTitical that the temperature not exceed a certain level. If the control valve fails in an open position, then the system will still maintain cooling even if system power or control is lost for one reason or another. 

The BOP system was neither designed nor tested for the dynamic conditions that existed at the time of the accident. Furthermore, the design, test, operation, and maintenance of the BOP system were not consistent with a high-reliability, fail-safe device. 

In some cases the electrodes are backed with expanded metal or screen to enhance electrical conductivity and mechanical strength. The button battery does not have a resealable fail-safe device, but its construction allows the battery to expand, either breaking the electrical continuity or opening the seal to relieve excess pressure caused by an abnormal circumstance. Button batteries are very suitable for low-current, low-overcharge-rate applications. 

Increase FT by 1 if SFF < 60% (normally applies to a non-fail-safe device to be avoided anyway). 

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