Flammability inert gases

Vapor Treatment. The vapors from the tank space can be sent to a treatment system (condenser, absorption, etc.) before venting. The system shown in Fig. 9.1 uses a vacuum-pressure relief valve which allows air in from the atmosphere when the liquid level falls (Fig. 9.1a) but forces the vapor through a treatment system when the tank is filled (Fig. 9.16). If inert gas blanketing is required, because of the flammable nature of the material, then a similar system can be adopted which draws inert gas rather than air when the liquid level falls. 

Inert Gas Dilution. Inert gas dilution involves the use of additives that produce large volumes of noncombustible gases when the polymer is decomposed. These gases dilute the oxygen supply to the flame or dilute the fuel concentration below the flammability limit. Metal hydroxides, metal carbonates, and some nitrogen-producing compounds function in this way as flame retardants (see Flame retardants, antimony and other inorganic compounds). 

Waste facihties should be designed to prevent explosions in sewer systems and typically are comprised of suitable traps, vents, clean-outs, collecting chambers, etc. Flammable gas detectors are installed in sewers to warn of ha2ardous concentrations, and inert gas blanketing of closed process sumps generally is advisable. 

Mixing cellulose esters in nonpolar hydrocarbons, such as toluene or xylene, may result in static electricity buildup that can cause a flash fire or explosion. When adding cellulose esters to any flammable Hquid, an inert gas atmosphere should be maintained within the vessel (132). This risk may be reduced by the use of conductive solvents in combination with the hydrocarbon or by use of an antistatic additive. Protective clothing and devices should be provided. 

Safe dilution requirements can be given for the gas phase in a flammability diagram or equation (270,273). Alternatively, safe vapor dilution can be given in terms of the Hquid storage conditions where allowance can be made for solubility of the inert gas in Hquid ethylene oxide (273). 

For flammable and/or toxic materials all of the precautions for a pressurized system should be considered. For example, when a centrifuge is pressurized, overpressure protection is required, even if the pressurization is an inert gas. Relieving of the pressure to a closed system or safe location must be considered. 

For reactors containing flammable liquids, where the reactor design pressure is insufficient to contain a deflagration, consideration should be given to providing an inert gas blanket (usually nitrogen). 

Provide automatic sprinkler system/inerting gas Provide deflagration vents Provide deflagration suppression system Monitor flammable atmosphere/fire Provide nitrogen blocks (nitrogen injection to stop flame propagation) or other explosion isolation measures... 

Inert gas not present leading to creation of flammable atmosphere. 

Prevention of a flammable atmosphere may be accomplished using any of the alternatives presented in NEPA 69. in cases where fuel concentration cannot be limited, the most common technique (inerting) is to add a suitable inert gas such as nitrogen, so that the residual oxygen concentration is insufficient to support a flame. A safety factor is then applied. Eor most flammable gases and vapors this typically involves reducing the oxygen concentration to less than 5-8 vol% (see Chapter 2-7 of NEPA 69). 

Immediately after the running test, any compressor intended for toxic, hazardous, flammable, or hydrogen-rich service should be gas tested with an inert gas to the maximum seal design pressure. The test is held at least 30 minutes and the casing and its joints checked for leaks, using a soap bubble method or other suitable means for leak detection. When no leaks are detected, the compressor will be considered acceptable. 

INERTING Depression of the flammable limits of a flammable gas/vapour-air mixture by the addition of an inert gas, e.g. nitrogen, carbon dioxide, or similar mixtures, to render it nonflammable. 

The gas is non-flammable, and is used for inert gas purging. Because it is 1.5 times heavier than air it may accumulate at low level. The general handling precautions are those in Table 9.3. 

FIGURE 3-9. Effect of various gases on the flammability limits of methane-inert-gas-air mixtures at 25°C (77°F) and atmospheric pressure (Zabetakis 1965). 

Consideration shonld also be given to the possibility that the flame arrester may ping, which conld prodnce a vacnnm condition in a low-pressnre tank when the tank is primped out, and implode (collapse) the tank. This may reqnire the installation of a vacnnm breaker or a pressnre-vacnnm conservation valve. If the tank contents are flammable and admission of air may resnlt in an ignitable mixture, it may be necessary to install an inert gas blanketing system on the tank, actuated by a pressnre controller, which would admit a sufficient flow of inerting gas when a vacnnm condition is detected. 

Carbon dioxide systems-Tliis system can be used where there is a handling and storage of gaseous and flammable materials, electrical equipment, and hazardous solids by introducing an inert gas (such as carbon dioxide) into the area in order to reduce the concentration of oxygen to the point where the fire will be extinguished. 

Purging a system of flammable gas/vapor mixtures generally involves adding an inert gas such as nitrogen to the system. Sometimes the volumes of nitrogen are large, but it is still less expensive than most other nonflammable gas (even CO and C02 have to be used cautiously) and certainly air cannot be used because it introduces oxygen... 

The inert gas is added under pressure to the system to be purged. This is then vented or purged to the atmosphere, usually more than one cycle of pressurization followed by venting is necessary to drop the concentration of a specific flammable or toxic component to a pre-established level. 

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