Devices safety

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 pressure-relief valve is probably one of the most common applications of a safety device. If the pressure within the line exceeds a predetermined level, then the pressure-relief valve opens, relieving the dangerous pressure buildup. Another example is a fuse in an electrical cable. If the cable is electrically overloaded, the fuse will blow and cut electrical flow before the cable overheats and bums or the system is overstressed. 

Plastic injection molding machines are very common in many manufacturing plants around the world. Occasionally, the technician needs to reach inside the machine to clear out debris. Many hands and arms have been lost from trying to clean the debris while the machine was still powered on (though not running). An electrical interlock that automatically disconnects the power source when the inside envelope of the machine has been violated is another example of a safety device. 

Low-Pressure Seals. The electrolysis of salt is nearly unaffected by the operating pressure. The generation of chlorine gas therefore stops only when the current to the cells is cut off. If the forward flow of chlorine is impeded for any reason, the pressure in the gas-processing system will rise rapidly at a rate proportional to the cell current. 

Stopping electrolysis for every small upset elsewhere in the process is clearly undesirable. In order to provide a degree of redundancy to automatic shutdown devices, then, normal practice is to provide relief in the form of a water seal that allows the cell gas to vent at a rate equal to its production. The chlorine in this vent must not he allowed to enter the atmosphere. Its confinement is the subject of Section 9.1.10.3. 

The water seal is installed somewhere on the low-pressure side of the chlorine process, usually between the cell room and the cooling process of Fig. 9.12. It is in communication with the process by a branch on the main chlorine header, as indicated by Fig. 9.44. The branch line terminates inside the seal vessel, slightly below the surface of a pool of water. When the pressure in the gas line exceeds the difference between the water level and the bottom of the branch line, the seal breaks and gas escapes. A source of brine can be used in place of water consideration of the difference in density then is necessary when setting the height of the seal. 

The gas cools as it passes through the main header. Under normal conditions, therefore, condensate forms. If the seal connection is at the bottom of the header, there will be a continuous small flow of water into the seal pot and out of the overflow line, and the seal wiU automatically be kept intact. For a more positive indication that the seal is being maintained, however, the usual practice is to add a flow of water into the seal pot. This allows a failure signal if flow stops and also helps to replenish the seal after a release of gas. 

For smooth operation and in order to minimize velocity head losses, the end of the vent pipe must be level. Again to provide smooth flow, it is frequently notched or serrated. 

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Acetylene cylinders are fitted with safety devices to release the acetylene ia the event of fire. Cylinders manufactured ia the United States are equipped with safety devices which contain a fusible metal that melts at 100°C. In large cylinders the safety devices are ia the form of a replaceable, threaded steel plug with a core of fusible metal. Small cylinders (0.28 and 1.12 m 10 and 40 fT, respectively) may have the fusible metal ia passages ia the cylinder valve. 

Boron-10 has a natural abundance of 19.61 atomic % and a thermal neutron cross section of 3.837 x 10 m (3837 bams) as compared to the cross section of 5 x 10 m (0.005 bams). Boron-10 is used at 40—95 atomic % in safety devices and control rods of nuclear reactors. Its use is also intended for breeder-reactor control rods. 

LB = lens blocking W = work holding RS = radiation shielding FSD = fusible safety device PC = proof casting SMF = sheet metal forming ... 

Fusible Safety Devices. Low melting bismuth ahoys, especiahy those that are eutectic have found numerous uses in safety devices. These ahoys can be cast into any shape necessary in order to be used in a plug or switch that must function at a given temperature. 

Boron mixed with an oxidizer is used as a pyrotechnic. This ordnance appHcation for missiles and rockets is predominandy military. However, boron is also used in air bags, placed in automobiles as safety devices, for initiating the sodium azide [26628-22-8] which fiHs the bag with nitrogen (13). Other boron compounds are also used in the air-bag pyrotechnic appHcation. 

Although the ethyleneamines ate water soluble, soHd amine hydrates may form at certain concentrations that may plug processing equipment, vent lines, and safety devices. Hydrate formation usually can be avoided by insulating and heat tracing equipment to maintain a temperature of at least 50°C. Water cleanup of ethyleneamine equipment can result in hydrate formation even in areas where routine processing is nonaqueous. Use of warm water can reduce the extent of the problem. 

Peripheral Components In addition to the stack, a power supply, pumps for diluate and concentrate, instrumentation, tanks for cleaning, and other peripherals are required. Safety devices are mandatoiy given the dangers posed by electricity, hydrogen, and chlorine. 

Safety Devices Pressure relief devices, flame arresters, and methods for handhng effluent from controlled releases provide control of accidental undesirable events. Special equipment should be considered for highly toxic chemical service. The following matters are considered ... 

The sudden mixing of large amounts of reactants under heating, instead of cooling, caused a runaway reaction. Once the pressure reached 16 bar pressure safety devices were actuated, the temperature at that point had reached 160°C,... 

Some toll processes lend themselves to test runs in the pre-startup phase. Actual materials for the toll may be used in the test or substitute materials, typically with low hazard potential, are often used to simulate the charging, reaction, and physical changes to be accomplished in the toll. Flow control, temperature control, pressure control, mixing and transferring efficiency can be measured. Mechanical integrity can be verified in regard to pumps, seals, vessels, heat exchangers, and safety devices. 

Does the facility have a program for regular inspection and testing of process safety valves and other process safety devices including interlocks ... 

For protection and temperature control of the compressor the follow ing safety devices may be provided ... 

No safety devices are shown on the flowsheet and installation of those is the responsibility of the operator of the unit. 

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