31:(i.e. non-combustible) purge gas into a closed system (e.g. a container or a process vessel) to prevent the formation of an ignitable atmosphere. Purging relies on the principle that a combustible (or flammable) gas is able to undergo combustion (explode) only if mixed with air in the right proportions. The
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Prevention of accidental fires and explosions can also be achieved by controlling sources of ignition. Purging with an inert gas provides a higher degree of safety however, because the practice ensures that an ignitable mixture never forms. Purging can therefore be said to rely on primary
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Assume a closed system (e.g. a container or process vessel), initially containing air, which shall be prepared for safe introduction of a flammable gas, for instance as part of a start-up procedure. The system can be flushed with an
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in everyday language. This confusion may lead to dangerous situations. Carbon dioxide is a safe inert gas for purging. Carbon dioxide is an unsafe inert gas for inerting, as it may ignite the vapors and result in an explosion.
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It is useful with two terms for purging because purge-out-of-service requires much larger quantities of inert agent than purge-into-service. The terminology of German standards refers to purge-into-service as
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prevention, reducing the possibility of an explosion, whereas control of sources of ignition relies on secondary prevention, reducing the probability of an explosion. Primary prevention is also known as
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Assume a closed system containing a flammable gas, which shall be prepared for safe ingress of air, for instance as part of a shut-down procedure. The system can be flushed with an
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may be used. Nitrogen and carbon dioxide are unsuitable purge gases in some applications, as these gases may undergo chemical reaction with fine dusts of certain light metals.
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TRBS 2152 Teil 2 / TRGS 722. Vermeidung oder
Einschränkung gefährlicher explosionsfähiger Atmosphäre. Technische Regeln für Betriebssicherheit. Ausgabe: März 2012
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NFPA 56. Standard for Fire and
Explosion Prevention During Cleaning and Purging of Flammable Gas Piping Systems. National Fire Protection Association
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to reduce the concentration of oxygen so that when the flammable gas is admitted, an ignitable mixture cannot form. In NFPA 56, this is known as
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to reduce the concentration of the flammable gas so that when air is introduced, an ignitable mixture cannot form. In NFPA 56 this is known as
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228:"Carbon dioxide not suitable for extinguishment of smouldering silo fires: static electricity may cause silo explosion"
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Fighting
Smoldering Fires in Silos – A Cautionary Note on Using Carbon Dioxide. Guest post at
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Because an inert purge gas is used, the purge procedure may (erroneously) be referred to as
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Ashford, NA (1997). "Industrial safety: the neglected issue in industrial ecology".
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The purge gas is inert, i.e. by definition non-combustible, or more precisely,
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of the gas define those proportions, i.e. the ignitable range.
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Comparison with other explosion prevention practices
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168:Limiting oxygen concentration
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290:(1–2). Elsevier: 115–21.
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226:Hedlund, FH (2018).
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