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== Limiti ==
=== Donja granica zapaljivosti ===
===Lower flammability limit===
'''[[Lower flammable limit|Lower flammability limit]]''' (LFL): The lowest concentration (percentage) of a gas or a vapor in air capable of producing a flash of fire in the presence of an ignition source (arc, flame, heat). The term is considered by many safety professionals to be the same as the lower explosive level (LEL). At a concentration in air lower than the LFL, gas mixtures are "too lean" to burn.
Methane gas has an LFL of 4.4%.<ref>{{Cite web|url=https://www.engineeringtoolbox.com/explosive-concentration-limits-d_423.html|title = Gases - Explosion and Flammability Concentration Limits}}</ref> If the atmosphere has less than 4.4% methane, an explosion cannot occur even if a source of ignition is present. From the health and safety perspective, the LEL concentration is considered to be [[Immediately dangerous to life or health|Immediately Dangerous to Life or Health (IDLH)]], where a more stringent exposure limit does not exist for the flammable gas.<ref>{{Cite web|url=https://www.cdc.gov/niosh/docs/2014-100/pdfs/2014-100.pdf|title=Current Intelligence Bulletin #66: Derivation of Immediately Dangerous to Life or Health (IDLH) Values|date=November 2013|website=The National Institute for Occupational Safety and Health (NIOSH)|access-date=2018-02-11}}</ref> ▼
▲Methane'''[[Lower gasflammable haslimit|Donja angranica zapaljivosti]]''' (LFL ): ofNajniža 4koncentracija (procenat) gasa ili pare u vazduhu koja može da proizvede bljesak vatre u prisustvu izvora paljenja (luk, plamen, toplota). Mnogi stručnjaci za bezbednost smatraju da je termin isti kao niži nivo eksplozivnosti (LEL). Pri koncentraciji u vazduhu nižoj od LFL, mešavine gasova su „previše mršave“ da bi sagorele. Gas metan ima LFL od 4,4%.<ref>{{Cite web|url=https://www.engineeringtoolbox.com/explosive-concentration-limits-d_423.html|title = Gases - Explosion and Flammability Concentration Limits}}</ref> IfAko theatmosfera atmosphereima hasmanje less thanod 4 .,4% methanemetana, anne explosionmože cannotdoći occurdo eveneksplozije ifčak ani sourceako ofje ignitionprisutan isizvor presentpaljenja. FromIz theperspektive healthzdravlja andi safety perspectivebezbednosti, thekoncentracija LEL concentration is considered tose besmatra [[Immediately dangerous to life or health| Immediatelyneposredno Dangerousopasnom topo Lifeživot orili Healthzdravlje]] (IDLH) ]], wheregde ane morepostoji stringentstroža exposuregranica limitizloženosti does not exist for the flammablezapaljivom gasgasu.<ref>{{Cite web|url=https://www.cdc.gov/niosh/docs/2014-100/pdfs/2014-100.pdf|title=Current Intelligence Bulletin #66: Derivation of Immediately Dangerous to Life or Health (IDLH) Values|date=November 2013|website=The National Institute for Occupational Safety and Health (NIOSH)|access-date=2018-02-11}}</ref>
Percentage reading on combustible air monitors should not be confused with the LFL concentrations. [[Explosimeter]]s designed and calibrated to a specific gas may show the relative concentration of the atmosphere to the LFL—the LFL being 100%. A 5% displayed LFL reading for methane, for example, would be equivalent to 5% multiplied by 4.4%, or approximately 0.22% methane by volume at 20 degrees C. Control of the explosion hazard is usually achieved by sufficient natural or mechanical ventilation, to limit the concentration of flammable gases or vapors to a maximum level of 25% of their ''lower explosive or flammable limit''.
Očitavanje procenta na monitorima zapaljivog vazduha ne treba mešati sa LFL koncentracijama. [[Explosimeter|Eksplozimetri]] projektovani i kalibrisani za određeni gas mogu pokazati relativnu koncentraciju atmosfere u odnosu na LFL – LFL je 100%. Očitavanje LFL od 5% za metan, na primer, bilo bi ekvivalentno 5% pomnoženom sa 4,4%, ili približno 0,22% zapremine metana na 20 stepeni C°. Kontrola opasnosti od eksplozije se obično postiže dovoljnom prirodnom ili mehaničkom ventilacijom, da ograniči koncentraciju zapaljivih gasova ili para na maksimalni nivo od 25% njihove ''donje granice eksplozivnosti ili zapaljivosti''.
===Upper flammability limit===
'''Upper flammability limit''' (UFL): Highest concentration (percentage) of a gas or a vapor in air capable of producing a flash of fire in the presence of an ignition source (arc, flame, heat). Concentrations higher than UFL or UEL are "too rich" to burn. Operating above the UFL is usually avoided for safety because air leaking in can bring the mixture into combustibility range.
=== Gornja granica zapaljivosti ===
===Influence of temperature, pressure and composition===
Flammability limits of mixtures of several combustible gases can be calculated using [[Henri Louis Le Chatelier|Le Chatelier's]] mixing rule for combustible volume fractions <math>x_i</math>:
'''Gornja granica zapaljivosti''' (UFL): Najviša koncentracija (procenat) gasa ili pare u vazduhu koja može da proizvede bljesak vatre u prisustvu izvora paljenja (luk, plamen, toplota). Koncentracije veće od UFL ili UEL su „prebogate” za sagorevanje. Rad iznad UFL se obično izbegava zbog bezbednosti, jer curenje vazduha može dovesti smešu u opseg zapaljivosti.
=== Uticaj temperature, pritiska i sastava ===
Granice zapaljivosti smeša nekoliko zapaljivih gasova mogu se izračunati korišćenjem [[Henri Louis Le Chatelier|Le Šateljeovog]] pravila mešanja za zapaljive zapreminske frakcije <math>x_i</math>:
: <math>LFL_{\text{mix}}=\frac{1}{\sum_i \frac{x_{i}}{LFL_{i}}}</math>
andi similarslično forza UFL.
[[Temperatura]], [[pritisak]] i koncentracija oksidatora takođe utiču na granice zapaljivosti. Viša temperatura ili pritisak, kao i veća koncentracija oksidatora (prvenstveno kiseonika u vazduhu), rezultiraju nižim LFL i većim UFL, te će gasna smeša lakše eksplodirati.
[[Temperature]], [[pressure]], and the concentration of the oxidizer also influences flammability limits. Higher temperature or pressure, as well as higher concentration of the oxidizer (primarily oxygen in air), results in lower LFL and higher UFL, hence the gas mixture will be easier to explode.
Obično atmosferski vazduh snabdeva kiseonik za sagorevanje, a granice pretpostavljaju normalnu koncentraciju kiseonika u vazduhu. Atmosfere obogaćene kiseonikom poboljšavaju sagorevanje, smanjujući LFL i povećavajući UFL, i obrnuto; atmosfera bez oksidatora nije ni zapaljiva ni eksplozivna za bilo koju koncentraciju goriva (osim za gasove koji se mogu energetski razložiti čak i u odsustvu oksidatora, kao što je [[acetilen]]). Značajno povećanje udela inertnih gasova u smeši vazduha, na račun kiseonika, povećava LFL i smanjuje UFL.
Usually atmospheric air supplies the oxygen for combustion, and limits assume the normal concentration of oxygen in air. Oxygen-enriched atmospheres enhance combustion, lowering the LFL and increasing the UFL, and vice versa; an atmosphere devoid of an oxidizer is neither flammable nor explosive for any fuel concentration (except for gases that can energetically decompose even in the absence of an oxidizer, such as [[acetylene]]). Significantly increasing the fraction of inert gases in an air mixture, at the expense of oxygen, increases the LFL and decreases the UFL.
== Reference ==
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