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Flammability limit
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<h2 id="violence-of-combustion">Violence of combustion</h2> <p>Combustion can vary in degree of violence. A <a href="/facts/Deflagration/wIR4pGtC">deflagration</a> is a propagation of a combustion zone at a velocity less than the speed of sound in the unreacted medium. A <a href="/facts/Detonation/C8cVTb2R">detonation</a> is a propagation of a combustion zone at a velocity greater than the speed of sound in the unreacted medium. An <a href="/facts/Explosion/Utp8Wv9D">explosion</a> is the bursting or rupture of an enclosure or container due to the development of internal pressure from a deflagration or detonation as defined in <a href="/facts/National_Fire_Protection_Association/lt5tWy0e">NFPA</a> 69. </p> <h2 id="limits">Limits</h2> <p>Any mixture of combustibles has specific lower and upper flammability limits. These limits are a function of the <a href="/facts/Pressure/eyc37GRG">pressure</a>, <a href="/facts/Temperature/QyGe4gmj">temperature</a> and <a href="/facts/Composition/0p5x6AQl">composition</a>. These limits are often shown in <a href="/facts/Flammability_diagram/Bwl57866">flammability diagrams</a> for which an example can be found in the work by Bee and Börner.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> </p> <h3>Lower flammability limit</h3> <p><a href="/facts/Lower_flammable_limit/gp4wdIIJ">Lower flammability limit</a> (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%.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> 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 <a href="/facts/Immediately_dangerous_to_life_or_health/ektUbSdQ">Immediately Dangerous to Life or Health (IDLH)</a>, where a more stringent exposure limit does not exist for the flammable gas.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p><p>Percentage reading on combustible air monitors should not be confused with the LFL concentrations. <a href="/facts/Explosimeter/7NulIopw">Explosimeters</a> 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 <i>lower explosive or flammable limit</i>. </p> <h3>Upper flammability limit</h3> <p>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. </p> <h3>Influence of temperature, pressure and composition</h3> <p>Flammability limits of mixtures of several combustible gases can be calculated using <a href="/facts/Henri_Louis_Le_Chatelier/VsGtL9BI">Le Chatelier's</a> mixing rule for combustible volume fractions x i {\displaystyle x_{i}} : </p> L F L mix = 1 ∑ i x i L F L i {\displaystyle LFL_{\text{mix}}={\frac {1}{\sum _{i}{\frac {x_{i}}{LFL_{i}}}}}} <p>and similar for UFL. </p><p><a href="/facts/Temperature/QyGe4gmj">Temperature</a>, <a href="/facts/Pressure/eyc37GRG">pressure</a>, 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. </p><p>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 <a href="/facts/Acetylene/yaDh6cmJ">acetylene</a>). Significantly increasing the fraction of inert gases in an air mixture, at the expense of oxygen, increases the LFL and decreases the UFL. </p> <h2 id="controlling-explosive-atmospheres">Controlling explosive atmospheres</h2> <h3>Gas and vapor</h3> <p>Controlling gas and vapor concentrations outside the flammable limits is a major consideration in <a href="/facts/Occupational_safety_and_health/ko1IeS92">occupational safety and health</a>. Methods used to control the concentration of a potentially explosive gas or vapor include use of sweep gas, an unreactive gas such as <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a> or <a href="/facts/Argon/QX6NRH6d">argon</a> to dilute the explosive gas before coming in contact with air. Use of scrubbers or <a href="/facts/Adsorption/ARH9peYM">adsorption</a> resins to remove explosive gases before release are also common. Gases can also be maintained safely at concentrations above the UEL, although a breach in the storage container can lead to explosive conditions or intense <a href="/facts/Fire/M6XwR3am">fires</a>. </p> <h3>Dusts</h3> <p>Dusts also have upper and lower explosion limits, though the upper limits are hard to measure and of little practical importance. Lower flammability limits for many organic materials are in the range of 10–50 g/m3, which is much higher than the limits set for health reasons, as is the case for the LEL of many gases and vapours. Dust clouds of this concentration are hard to see through for more than a short distance, and normally only exist inside process equipment. </p><p>Flammability limits also depend on the particle size of the dust involved, and are not intrinsic properties of the material. In addition, a concentration above the LEL can be created suddenly from settled dust accumulations, so management by routine monitoring, as is done with gases and vapours, is of no value. The preferred method of managing combustible dust is by preventing accumulations of settled dust through process enclosure, ventilation, and surface cleaning. However, lower flammability limits may be relevant to plant design. </p> <h3>Volatile liquids</h3> <p>Situations caused by evaporation of flammable liquids into the air-filled void volume of a container may be limited by flexible container volume or by using an immiscible fluid to fill the void volume. <a href="/facts/Hydraulic_tanker/Mcb9d2qo">Hydraulic tankers</a> use displacement of water when filling a tank with petroleum.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p> <h2 id="examples">Examples</h2> <p>The flammable/explosive limits of some gases and vapors are given below. Concentrations are given in percent by volume of air. </p> <ul><li>Class IA liquids with a <a href="/facts/Flash_point/97JQP35E">flash point</a> less than 73 °F (23 °C) and <a href="/facts/Boiling_point/E2BK9QoS">boiling point</a> less than 100 °F (38 °C) have a <a href="/facts/NFPA_704/7IgHH9Dv">NFPA 704</a> flammability rating of 4</li> <li>Class IB liquids with a flash point less than 73 °F (23 °C) and a boiling point equal to or greater than 100 °F (38 °C) and class IC liquids with a flash point equal to or greater than 73 °F (23 °C), but less than 100 °F (38 °C) have a NFPA 704 flammability rating of 3</li> <li>Class II liquids with a flash point equal to or greater than 100 °F (38 °C), but less than 140 °F (60 °C) and class IIIA liquids with a flash point equal to or greater than 140 °F (60 °C), but less than 200 °F (93 °C) have a NFPA 704 flammability rating of 2</li> <li>Class IIIB liquids with a flash point equal to or greater than 200 °F (93 °C) have a NFPA 704 flammability rating of 1</li></ul> <table><tbody><tr><th rowspan="2" colspan="2">Substance</th><th colspan="2">Flammability limit (%vol.)</th><th rowspan="2"><a href="/facts/National_Fire_Protection_Association/lt5tWy0e">NFPA</a> class</th><th rowspan="2"><a href="/facts/Flash_point/97JQP35E">Flash point</a></th><th rowspan="2"><a href="/facts/Minimum_ignition_energy/GqkgPvo0">Minimum ignition energy</a> (mJ) @ proportion in air at which achieved<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a><a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a></th><th rowspan="2">Autoignition temperature</th></tr><tr><th>Lower</th><th>Upper</th></tr><tr><td colspan="2"><a href="/facts/Acetaldehyde/QllLbSUe">Acetaldehyde</a></td><td>4.0</td><td>57.0</td><td>IA</td><td>−39 °C</td><td>0.37</td><td>175 °C</td></tr><tr><td colspan="2"><a href="/facts/Acetic_acid/uyBKA2Pd">Acetic acid</a> (glacial)</td><td>4</td><td>19.9</td><td>II</td><td>39–43 °C</td><td></td><td>463 °C</td></tr><tr><td colspan="2"><a href="/facts/Acetic_anhydride/hGxHam3M">Acetic anhydride</a></td><td></td><td></td><td>II</td><td>54 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Acetone/cVyJxKqw">Acetone</a></td><td>2.6–3</td><td>12.8–13</td><td>IB</td><td>−17 °C</td><td>1.15 @ 4.5%</td><td>465 °C, 485 °C<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a></td></tr><tr><td colspan="2"><a href="/facts/Acetonitrile/fNpbvRp6">Acetonitrile</a></td><td></td><td></td><td>IB</td><td>2 °C</td><td></td><td>524 °C</td></tr><tr><td colspan="2"><a href="/facts/Acetyl_chloride/SU9Bq4tG">Acetyl chloride</a></td><td>7.3</td><td>19</td><td>IB</td><td>5 °C</td><td></td><td>390 °C</td></tr><tr><td colspan="2"><a href="/facts/Acetylene/yaDh6cmJ">Acetylene</a></td><td>2.5</td><td>100<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a></td><td>IA</td><td>Flammable gas</td><td>0.017 @ 8.5%; 0.0002 @ 40%, in pure oxygen</td><td>305 °C</td></tr><tr><td colspan="2"><a href="/facts/Acrolein/1gdt9D3f">Acrolein</a></td><td>2.8</td><td>31</td><td>IB</td><td>−26 °C</td><td>0.13</td><td></td></tr><tr><td colspan="2"><a href="/facts/Acrylonitrile/zvhfg050">Acrylonitrile</a></td><td>3.0</td><td>17.0</td><td>IB</td><td>0 °C</td><td>0.16 @ 9.0%</td><td></td></tr><tr><td colspan="2"><a href="/facts/Allyl_chloride/saGo9WGr">Allyl chloride</a></td><td>2.9</td><td>11.1</td><td>IB</td><td>−32 °C</td><td>0.77</td><td></td></tr><tr><td colspan="2"><a href="/facts/Ammonia/MtLtJFtz">Ammonia</a></td><td>15</td><td>28</td><td>IIIB</td><td>11 °C</td><td>680</td><td>651 °C</td></tr><tr><td colspan="2"><a href="/facts/Arsine/VkH6217V">Arsine</a></td><td>4.5–5.1<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a></td><td>78</td><td>IA</td><td>Flammable gas</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Benzene/Fguue7nr">Benzene</a></td><td>1.2</td><td>7.8</td><td>IB</td><td>−11 °C</td><td>0.2 @ 4.7%</td><td>560 °C</td></tr><tr><td colspan="2"><a href="/facts/1%2c3-Butadiene/j9W2LxGv">1,3-Butadiene</a></td><td>2.0</td><td>12</td><td>IA</td><td>−85 °C</td><td>0.13 @ 5.2%</td><td></td></tr><tr><td colspan="2"><a href="/facts/Butane/InIHpYlY">Butane</a>, <a href="/facts/N-butane/InIHpYlY">n-butane</a></td><td>1.6</td><td>8.4</td><td>IA</td><td>−60 °C</td><td>0.25 @ 4.7%</td><td>420–500 °C</td></tr><tr><td colspan="2"><a href="/facts/Butyl_acetate/2tUouhQr">n-Butyl acetate</a>, butyl acetate</td><td>1–1.7<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a></td><td>8–15</td><td>IB</td><td>24 °C</td><td></td><td>370 °C</td></tr><tr><td colspan="2"><a href="/facts/2-Butanol/JAJvawVN">2-Butanol</a></td><td>1.7</td><td>9.8</td><td></td><td>29 °C</td><td></td><td>405 °C</td></tr><tr><td colspan="2"><a href="/facts/Isobutanol/JNB4Hh9W">Isobutanol</a></td><td>1.7</td><td>10.9</td><td></td><td>22–27 °C</td><td></td><td>415 °C</td></tr><tr><td colspan="2"><a href="/facts/N-Butanol/GlSNHexW">n-Butanol</a></td><td>1.4<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a></td><td>11.2</td><td>IC</td><td>35 °C</td><td></td><td>340 °C</td></tr><tr><td colspan="2"><a href="/facts/N-Butyl_chloride/MB2GasS1">n-Butyl chloride</a>, 1-chlorobutane</td><td>1.8</td><td>10.1</td><td>IB</td><td>−6 °C</td><td>1.24</td><td></td></tr><tr><td colspan="2"><a href="/facts/N-Butyl_mercaptan/XdvCoblb">n-Butyl mercaptan</a></td><td>1.4<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a></td><td>10.2</td><td>IB</td><td>2 °C</td><td></td><td>225 °C</td></tr><tr><td colspan="2"><a href="/facts/Butyl_methyl_ketone/5kpvjMAB">Butyl methyl ketone</a>, <a href="/facts/2-hexanone/5kpvjMAB">2-hexanone</a></td><td>1<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a></td><td>8</td><td>IC</td><td>25 °C</td><td></td><td>423 °C</td></tr><tr><td colspan="2"><a href="/facts/Butylene/6JdB9n0U">Butylene</a>, 1-butylene, 1-butene</td><td>1.98<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a></td><td>9.65</td><td>IA</td><td>−80 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Carbon_disulfide/b04Tadmy">Carbon disulfide</a></td><td>1.0</td><td>50.0</td><td>IB</td><td>−30 °C</td><td>0.009 @ 7.8%</td><td>90 °C</td></tr><tr><td colspan="2"><a href="/facts/Carbon_monoxide/CKuLtEMJ">Carbon monoxide</a></td><td>12<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a></td><td>75</td><td>IA</td><td>−191 °C Flammable gas</td><td></td><td>609 °C</td></tr><tr><td colspan="2"><a href="/facts/Chlorine_monoxide/ajDtLjlS">Chlorine monoxide</a></td><td></td><td></td><td>IA</td><td>Flammable gas</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/1-Chloro-1%2c1-difluoroethane/xUUAk21w">1-Chloro-1,1-difluoroethane</a></td><td>6.2</td><td>17.9</td><td>IA</td><td>−65 °C Flammable gas</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Cyanogen/nsKahJy2">Cyanogen</a></td><td>6.0–6.6<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a></td><td>32–42.6</td><td>IA</td><td>Flammable gas</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Cyclobutane/hzsbc9ML">Cyclobutane</a></td><td>1.8</td><td>11.1</td><td>IA</td><td>−63.9 °C<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a></td><td></td><td>426.7 °C</td></tr><tr><td colspan="2"><a href="/facts/Cyclohexane/FDAW5j8v">Cyclohexane</a></td><td>1.3</td><td>7.8–8</td><td>IB</td><td>−18 – −20 °C<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a></td><td>0.22 @ 3.8%</td><td>245 °C</td></tr><tr><td colspan="2"><a href="/facts/Cyclohexanol/kHdlHrys">Cyclohexanol</a></td><td>1</td><td>9</td><td>IIIA</td><td>68 °C</td><td></td><td>300 °C</td></tr><tr><td colspan="2"><a href="/facts/Cyclohexanone/Hf3YTWjB">Cyclohexanone</a></td><td>1–1.1</td><td>9–9.4</td><td>II</td><td>43.9–44 °C</td><td></td><td>420 °C<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a></td></tr><tr><td colspan="2"><a href="/facts/Cyclopentadiene/S66eVYvh">Cyclopentadiene</a><a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a></td><td></td><td></td><td>IB</td><td>0 °C</td><td>0.67</td><td>640 °C</td></tr><tr><td colspan="2"><a href="/facts/Cyclopentane/co1ppLTk">Cyclopentane</a></td><td>1.5–2</td><td>9.4</td><td>IB</td><td>−37 – −38.9 °C<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a><a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a></td><td>0.54</td><td>361 °C</td></tr><tr><td colspan="2"><a href="/facts/Cyclopropane/BAUAYB7s">Cyclopropane</a></td><td>2.4</td><td>10.4</td><td>IA</td><td>−94.4 °C<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a></td><td>0.17 @ 6.3%</td><td>498 °C</td></tr><tr><td colspan="2"><a href="/facts/Decane/KPn6cJbz">Decane</a></td><td>0.8</td><td>5.4</td><td>II</td><td>46.1 °C</td><td></td><td>210 °C</td></tr><tr><td colspan="2"><a href="/facts/Diborane/k7egwbPf">Diborane</a></td><td>0.8</td><td>88</td><td>IA</td><td>−90 °C Flammable gas<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a></td><td></td><td>38 °C</td></tr><tr><td colspan="2"><a href="/facts/O-Dichlorobenzene/Ym7JtkQJ">o-Dichlorobenzene</a>, 1,2-dichlorobenzene</td><td>2<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a></td><td>9</td><td>IIIA</td><td>65 °C</td><td></td><td>648 °C</td></tr><tr><td colspan="2"><a href="/facts/1%2c1-Dichloroethane/Do3v9jKL">1,1-Dichloroethane</a></td><td>6</td><td>11</td><td>IB</td><td>14 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/1%2c2-Dichloroethane/WfKddRda">1,2-Dichloroethane</a></td><td>6</td><td>16</td><td>IB</td><td>13 °C</td><td></td><td>413 °C</td></tr><tr><td colspan="2"><a href="/facts/1%2c1-Dichloroethene/eWgracNP">1,1-Dichloroethene</a></td><td>6.5</td><td>15.5</td><td>IA</td><td>−10 °C Flammable gas</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Dichlorofluoromethane/9YtbtHSL">Dichlorofluoromethane</a></td><td></td><td>54.7</td><td></td><td>Non flammable,<a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a> −36.1 °C<a class="footnote-ref" id="fnref:27" href="#fn:27"><sup>27</sup></a></td><td></td><td>552 °C</td></tr><tr><td colspan="2"><a href="/facts/Dichloromethane/mHyeTD2D">Dichloromethane</a>, methylene chloride</td><td>16</td><td>66</td><td></td><td>Non flammable</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Dichlorosilane/3BG7FIcF">Dichlorosilane</a></td><td>4–4.7</td><td>96</td><td>IA</td><td>−28 °C</td><td>0.015</td><td></td></tr><tr><td colspan="2"><a href="/facts/Diesel_fuel/lm71xc19">Diesel fuel</a></td><td>0.6</td><td>7.5</td><td>IIIA</td><td>>62 °C</td><td></td><td>210 °C</td></tr><tr><td colspan="2"><a href="/facts/Diethanolamine/Tu33IQqc">Diethanolamine</a></td><td>2</td><td>13</td><td>IB</td><td>169 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Diethylamine/wlVINVXe">Diethylamine</a></td><td>1.8</td><td>10.1</td><td>IB</td><td>−23 – −26 °C</td><td></td><td>312 °C</td></tr><tr><td colspan="2">Diethyl disulfide</td><td>1.2</td><td></td><td>II</td><td>38.9 °C<a class="footnote-ref" id="fnref:28" href="#fn:28"><sup>28</sup></a></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Diethyl_ether/Ep20vEdj">Diethyl ether</a></td><td>1.9–2</td><td>36–48</td><td>IA</td><td>−45 °C</td><td>0.19 @ 5.1%</td><td>160–170 °C</td></tr><tr><td colspan="2"><a href="/facts/Diethyl_sulfide/URzDh77Q">Diethyl sulfide</a></td><td></td><td></td><td>IB</td><td>−10 °C<a class="footnote-ref" id="fnref:29" href="#fn:29"><sup>29</sup></a></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/1%2c1-Difluoroethane/STzHeaxv">1,1-Difluoroethane</a></td><td>3.7</td><td>18</td><td>IA</td><td>−81.1 °C<a class="footnote-ref" id="fnref:30" href="#fn:30"><sup>30</sup></a></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/1%2c1-Difluoroethylene/xoyVF5Pn">1,1-Difluoroethylene</a></td><td>5.5</td><td>21.3</td><td></td><td>−126.1 °C<a class="footnote-ref" id="fnref:31" href="#fn:31"><sup>31</sup></a></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Difluoromethane/XQ4tkYVJ">Difluoromethane</a></td><td>14.4<a class="footnote-ref" id="fnref:32" href="#fn:32"><sup>32</sup></a></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td colspan="2">Diisobutyl ketone</td><td>1</td><td>6</td><td></td><td>49 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Diisopropyl_ether/FvSKHafv">Diisopropyl ether</a></td><td>1</td><td>21</td><td>IB</td><td>−28 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Dimethylamine/6ehYB5m0">Dimethylamine</a></td><td>2.8</td><td>14.4</td><td>IA</td><td>Flammable gas</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/1%2c1-Dimethylhydrazine/g08Fzo2D">1,1-Dimethylhydrazine</a></td><td></td><td></td><td>IB</td><td></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Dimethyl_sulfide/mUrg1jol">Dimethyl sulfide</a></td><td></td><td></td><td>IA</td><td>−49 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Dimethyl_sulfoxide/T4HSYfuC">Dimethyl sulfoxide</a></td><td>2.6–3</td><td>42</td><td>IIIB</td><td>88–95 °C</td><td></td><td>215 °C</td></tr><tr><td colspan="2"><a href="/facts/1%2c4-Dioxane/ILtQeBxC">1,4-Dioxane</a></td><td>2</td><td>22</td><td>IB</td><td>12 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Epichlorohydrin/pouNHADT">Epichlorohydrin</a></td><td>4</td><td>21</td><td></td><td>31 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Ethane/BGCzc6yh">Ethane</a></td><td>3<a class="footnote-ref" id="fnref:33" href="#fn:33"><sup>33</sup></a></td><td>12–12.4</td><td>IA</td><td>Flammable gas, −135 °C</td><td></td><td>515 °C</td></tr><tr><td colspan="2"><a href="/facts/Ethanol/3lCLfBSP">Ethanol</a>, ethyl alcohol</td><td>3–3.3</td><td>19</td><td>IB</td><td>12.8 °C</td><td></td><td>365 °C</td></tr><tr><td colspan="2"><a href="/facts/2-Ethoxyethanol/qMGX9nl7">2-Ethoxyethanol</a></td><td>3</td><td>18</td><td></td><td>43 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/2-Ethoxyethyl_acetate/WFkPq8fF">2-Ethoxyethyl acetate</a></td><td>2</td><td>8</td><td></td><td>56 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Ethyl_acetate/om0PFI7S">Ethyl acetate</a></td><td>2</td><td>12</td><td>IA</td><td>−4 °C</td><td></td><td>460 °C</td></tr><tr><td colspan="2"><a href="/facts/Ethylamine/Tj9X5ESb">Ethylamine</a></td><td>3.5</td><td>14</td><td>IA</td><td>−17 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Ethylbenzene/aVhfY3vX">Ethylbenzene</a></td><td>1.0</td><td>7.1</td><td></td><td>15–20 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Ethylene/QMNBYLYn">Ethylene</a></td><td>2.7</td><td>36</td><td>IA</td><td></td><td>0.07</td><td>490 °C</td></tr><tr><td colspan="2"><a href="/facts/Ethylene_glycol/stFz6CVe">Ethylene glycol</a></td><td>3</td><td>22</td><td></td><td>111 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Ethylene_oxide/4WDVKX2r">Ethylene oxide</a></td><td>3</td><td>100</td><td>IA</td><td>−20 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Ethyl_chloride/6DjUIuH7">Ethyl chloride</a></td><td>3.8<a class="footnote-ref" id="fnref:34" href="#fn:34"><sup>34</sup></a></td><td>15.4</td><td>IA</td><td>−50 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Ethyl_mercaptan/3zjKzHH4">Ethyl mercaptan</a></td><td></td><td></td><td>IA</td><td></td><td></td><td></td></tr><tr><td colspan="2">Fuel oil No.1</td><td>0.7<a class="footnote-ref" id="fnref:35" href="#fn:35"><sup>35</sup></a></td><td>5</td><td></td><td></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Furan/XCEMqxER">Furan</a></td><td>2</td><td>14</td><td>IA</td><td>−36 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Gasoline/lcnxq5BS">Gasoline</a> (100 <a href="/facts/Octane/3E91j6Fe">octane</a>)</td><td>1.4</td><td>7.6</td><td>IB</td><td>< −40 °C</td><td></td><td>246–280 °C</td></tr><tr><td colspan="2"><a href="/facts/Glycerol/sRQ6NBQQ">Glycerol</a></td><td>3</td><td>19</td><td></td><td>199 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Heptane/jP4XjrBe">Heptane</a>, n-heptane</td><td>1.05</td><td>6.7</td><td></td><td>−4 °C</td><td>0.24 @ 3.4%</td><td>204–215 °C</td></tr><tr><td colspan="2"><a href="/facts/Hexane/JxPecNPt">Hexane</a>, n-hexane</td><td>1.2</td><td>7.5</td><td></td><td>−22 °C</td><td>0.24 @ 3.8%</td><td>225 °C, 233 °C<a class="footnote-ref" id="fnref:36" href="#fn:36"><sup>36</sup></a></td></tr><tr><td colspan="2"><a href="/facts/Hydrogen/BoYHjl0J">Hydrogen</a></td><td>4/18.3<a class="footnote-ref" id="fnref:37" href="#fn:37"><sup>37</sup></a></td><td>75/59</td><td>IA</td><td>Flammable gas</td><td>0.016 @ 28%; 0.0012, in pure oxygen</td><td>500–571 °C</td></tr><tr><td colspan="2"><a href="/facts/Hydrogen_sulfide/UbCqjMMk">Hydrogen sulfide</a></td><td>4.3</td><td>46</td><td>IA</td><td>Flammable gas</td><td>0.068</td><td></td></tr><tr><td colspan="2"><a href="/facts/Isobutane/Bd8H7rsH">Isobutane</a></td><td>1.8<a class="footnote-ref" id="fnref:38" href="#fn:38"><sup>38</sup></a></td><td>9.6</td><td>IA</td><td>Flammable gas</td><td></td><td>462 °C</td></tr><tr><td colspan="2"><a href="/facts/Isobutyl_alcohol/JNB4Hh9W">Isobutyl alcohol</a></td><td>2</td><td>11</td><td></td><td>28 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Isophorone/m4D1Y9PI">Isophorone</a></td><td>1</td><td>4</td><td></td><td>84 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Isopropyl_alcohol/7KqgIkUd">Isopropyl alcohol</a>, isopropanol</td><td>2<a class="footnote-ref" id="fnref:39" href="#fn:39"><sup>39</sup></a></td><td>12</td><td>IB</td><td>12 °C</td><td></td><td>398–399 °C; 425 °C<a class="footnote-ref" id="fnref:40" href="#fn:40"><sup>40</sup></a></td></tr><tr><td colspan="2"><a href="/facts/Isopropyl_chloride/Ccvy9grm">Isopropyl chloride</a></td><td></td><td></td><td>IA</td><td></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Kerosene/DoHPYXKp">Kerosene</a> <a href="/facts/Jet_A-1/4CDswF3t">Jet A-1</a></td><td>0.6–0.7</td><td>4.9–5</td><td>II</td><td>>38 °C, as jet fuel</td><td></td><td>210 °C</td></tr><tr><td colspan="2"><a href="/facts/Lithium_hydride/uWCl2pST">Lithium hydride</a></td><td></td><td></td><td>IA</td><td></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/2-Mercaptoethanol/QfHQldp3">2-Mercaptoethanol</a></td><td></td><td></td><td>IIIA</td><td></td><td></td><td></td></tr><tr><td rowspan="2"><a href="/facts/Methane/kBHneYnh">Methane</a> (natural gas)</td><td>ISO10156</td><td>5.0</td><td>14.3</td><td rowspan="2">IA</td><td rowspan="2">Flammable gas</td><td rowspan="2">0.21 @ 8.5%</td><td rowspan="2">580 °C</td></tr><tr><td>IEC60079-20-1</td><td>4.4</td><td>17</td></tr><tr><td colspan="2"><a href="/facts/Methyl_acetate/dKzfLaUU">Methyl acetate</a></td><td>3</td><td>16</td><td></td><td>−10 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Methyl_alcohol/EIfpoNCg">Methyl alcohol</a>, methanol</td><td>6–6.7<a class="footnote-ref" id="fnref:41" href="#fn:41"><sup>41</sup></a></td><td>36</td><td>IB</td><td>11 °C</td><td></td><td>385 °C; 455 °C<a class="footnote-ref" id="fnref:42" href="#fn:42"><sup>42</sup></a></td></tr><tr><td colspan="2"><a href="/facts/Methylamine/srMMDp0D">Methylamine</a></td><td></td><td></td><td>IA</td><td>8 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Methyl_chloride/DvmeEgDS">Methyl chloride</a></td><td>10.7<a class="footnote-ref" id="fnref:43" href="#fn:43"><sup>43</sup></a></td><td>17.4</td><td>IA</td><td>−46 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Dimethyl_ether/XSo4RBvc">Methyl ether</a></td><td></td><td></td><td>IA</td><td>−41 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Methyl_ethyl_ether/m142lgbz">Methyl ethyl ether</a></td><td></td><td></td><td>IA</td><td></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Methyl_ethyl_ketone/kMEw9hTq">Methyl ethyl ketone</a></td><td>1.8<a class="footnote-ref" id="fnref:44" href="#fn:44"><sup>44</sup></a></td><td>10</td><td>IB</td><td>−6 °C</td><td></td><td>505–515 °C<a class="footnote-ref" id="fnref:45" href="#fn:45"><sup>45</sup></a></td></tr><tr><td colspan="2"><a href="/facts/Methyl_formate/cVvvNUNP">Methyl formate</a></td><td></td><td></td><td>IA</td><td></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Methyl_mercaptan/hKk384K1">Methyl mercaptan</a></td><td>3.9</td><td>21.8</td><td>IA</td><td>−53 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Mineral_spirits/qDgcURve">Mineral spirits</a></td><td>0.7<a class="footnote-ref" id="fnref:46" href="#fn:46"><sup>46</sup></a></td><td>6.5</td><td></td><td>38–43 °C</td><td></td><td>258 °C</td></tr><tr><td colspan="2"><a href="/facts/Morpholine/IePtCvsK">Morpholine</a></td><td>1.8</td><td>10.8</td><td>IC</td><td>31–37.7 °C</td><td></td><td>310 °C</td></tr><tr><td colspan="2"><a href="/facts/Naphthalene/RU2sV8mN">Naphthalene</a></td><td>0.9<a class="footnote-ref" id="fnref:47" href="#fn:47"><sup>47</sup></a></td><td>5.9</td><td>IIIA</td><td>79–87 °C</td><td></td><td>540 °C</td></tr><tr><td colspan="2"><a href="/facts/Neohexane/notN1bYC">Neohexane</a></td><td>1.19<a class="footnote-ref" id="fnref:48" href="#fn:48"><sup>48</sup></a></td><td>7.58</td><td></td><td>−29 °C</td><td></td><td>425 °C</td></tr><tr><td colspan="2"><a href="/facts/Nickel_tetracarbonyl/8Py5Dre1">Nickel tetracarbonyl</a></td><td>2</td><td>34</td><td></td><td>4 °C</td><td></td><td>60 °C</td></tr><tr><td colspan="2"><a href="/facts/Nitrobenzene/JCEYpjAA">Nitrobenzene</a></td><td>2</td><td>9</td><td>IIIA</td><td>88 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Nitromethane/mfVA2AA1">Nitromethane</a></td><td>7.3</td><td>22.2</td><td></td><td>35 °C</td><td></td><td>379 °C</td></tr><tr><td colspan="2"><a href="/facts/Octane/3E91j6Fe">Octane</a></td><td>1</td><td>7</td><td></td><td>13 °C</td><td></td><td></td></tr><tr><td colspan="2">iso-Octane</td><td>0.79</td><td>5.94</td><td></td><td></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Pentane/B5LzJ2zD">Pentane</a></td><td>1.5</td><td>7.8</td><td>IA</td><td>−40 – −49 °C</td><td>0.18 @ 4.4%, as 2-pentane</td><td>260 °C</td></tr><tr><td colspan="2"><a href="/facts/N-Pentane/B5LzJ2zD">n-Pentane</a></td><td>1.4</td><td>7.8</td><td>IA</td><td></td><td>0.28 @ 3.3%</td><td></td></tr><tr><td colspan="2">iso-Pentane</td><td>1.32<a class="footnote-ref" id="fnref:49" href="#fn:49"><sup>49</sup></a></td><td>9.16</td><td>IA</td><td></td><td></td><td>420 °C</td></tr><tr><td colspan="2"><a href="/facts/Phosphine/aYysn5TS">Phosphine</a></td><td></td><td></td><td>IA</td><td></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Propane/E0b23KGh">Propane</a></td><td>2.1</td><td>9.5–10.1</td><td>IA</td><td>Flammable gas</td><td>0.25 @ 5.2%; 0.0021, in pure oxygen</td><td>480 °C</td></tr><tr><td colspan="2"><a href="/facts/Propyl_acetate/BHCrp17K">Propyl acetate</a></td><td>2</td><td>8</td><td></td><td>13 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Propylene/5eLDmPvm">Propylene</a></td><td>2.0</td><td>11.1</td><td>IA</td><td>−108 °C</td><td>0.28</td><td>458 °C</td></tr><tr><td colspan="2"><a href="/facts/Propylene_oxide/XWz8SU72">Propylene oxide</a></td><td>2.9</td><td>36</td><td>IA</td><td></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Pyridine/X817hCch">Pyridine</a></td><td>2</td><td>12</td><td></td><td>20 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Silane/XNevDLgE">Silane</a></td><td>1.5<a class="footnote-ref" id="fnref:50" href="#fn:50"><sup>50</sup></a></td><td>98</td><td>IA</td><td></td><td></td><td><21 °C</td></tr><tr><td colspan="2"><a href="/facts/Styrene/B8uXm78L">Styrene</a></td><td>1.1</td><td>6.1</td><td>IB</td><td>31–32.2 °C</td><td></td><td>490 °C</td></tr><tr><td colspan="2"><a href="/facts/Tetrafluoroethylene/3lzA1S3E">Tetrafluoroethylene</a></td><td></td><td></td><td>IA</td><td></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Tetrahydrofuran/P5t6SkMK">Tetrahydrofuran</a></td><td>2</td><td>12</td><td>IB</td><td>−14 °C</td><td></td><td>321 °C</td></tr><tr><td colspan="2"><a href="/facts/Toluene/Pzdt8dwD">Toluene</a></td><td>1.2–1.27</td><td>6.75–7.1</td><td>IB</td><td>4.4 °C</td><td>0.24 @ 4.1%</td><td>480 °C; 535 °C<a class="footnote-ref" id="fnref:51" href="#fn:51"><sup>51</sup></a></td></tr><tr><td colspan="2"><a href="/facts/Triethylborane/qLlyzN2r">Triethylborane</a></td><td></td><td></td><td></td><td>−20 °C</td><td></td><td>−20 °C</td></tr><tr><td colspan="2"><a href="/facts/Trimethylamine/cj1dWmJq">Trimethylamine</a></td><td></td><td></td><td>IA</td><td>Flammable gas</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Trinitrobenzene/M8n9HhLo">Trinitrobenzene</a></td><td></td><td></td><td>IA</td><td></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Turpentine/ME2Lgu0K">Turpentine</a></td><td>0.8<a class="footnote-ref" id="fnref:52" href="#fn:52"><sup>52</sup></a></td><td></td><td>IC</td><td>35 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Vegetable_oil/70v8uQMH">Vegetable oil</a></td><td></td><td></td><td>IIIB</td><td>327 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Vinyl_acetate/qVdoopEo">Vinyl acetate</a></td><td>2.6</td><td>13.4</td><td></td><td>−8 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Vinyl_chloride/UNGUdwTK">Vinyl chloride</a></td><td>3.6</td><td>33</td><td></td><td></td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/Xylene/BEGggD9s">Xylenes</a></td><td>0.9–1.0</td><td>6.7–7.0</td><td>IC</td><td>27–32 °C</td><td>0.2</td><td></td></tr><tr><td colspan="2"><a href="/facts/M-Xylene/R18IDFIS">m-Xylene</a></td><td>1.1<a class="footnote-ref" id="fnref:53" href="#fn:53"><sup>53</sup></a></td><td>7</td><td>IC</td><td>25 °C</td><td></td><td>525 °C</td></tr><tr><td colspan="2"><a href="/facts/O-Xylene/lCELfssz">o-Xylene</a></td><td></td><td></td><td>IC</td><td>17 °C</td><td></td><td></td></tr><tr><td colspan="2"><a href="/facts/P-Xylene/PUyGrJSe">p-Xylene</a></td><td>1.0</td><td>6.0</td><td>IC</td><td>27.2 °C</td><td></td><td>530 °C</td></tr></tbody></table> <h2 id="astm-e681">ASTM E681</h2> <p>In the U.S. the most common method of measuring LFLs and UFLs is <a href="https://www.astm.org/Standards/E681.htm">ASTM E681</a>.<a class="footnote-ref" id="fnref:54" href="#fn:54"><sup>54</sup></a> This standard test is required for <a href="/facts/HAZMAT_Class_2_Gases/JGghroAY">HAZMAT Class 2 Gases</a> and for determining <a href="/facts/Refrigerant/rI60t5zU">refrigerant</a> flammability classifications. This standard uses visual observations of flame propagation in 5 or 12 L spherical glass vessels to measure the flammability limits. Flammable conditions are defined as those for which a flame propagates outside a 90° cone angle. </p> <h2 id="see-also">See also</h2> <ul> <li>Chemistry portal</li></ul> <ul><li><a href="/facts/ATEX/YRKw5kNj">ATEX</a></li> <li><a href="/facts/Flammability/1QexTQ4T">Flammability</a></li> <li><a href="/facts/Limiting_oxygen_concentration/4e7nk4Cs">Limiting oxygen concentration</a></li> <li><a href="/facts/Minimum_ignition_energy/GqkgPvo0">Minimum ignition energy</a></li></ul> <h2 id="further-reading">Further reading</h2> <ul><li>David R. Lide, Editor-in-Chief; <i>CRC Handbook of Chemistry and Physics, 72nd edition</i>; CRC Press; <a href="/facts/Boca_Raton%2c_Florida/9gcNen3S">Boca Raton</a>, Florida; 1991; <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 0-8493-0565-9</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Bee, A.; Börner, M. (2023). "Laminar Burning Speeds and Flammability Limits of CH4/O2 Mixtures With Varying N2 Dilution at Sub-Atmospheric Conditions" (PDF). Combustion Science and Technology. 195 (8). Taylor & Francis: 1910--1929. doi:10.1080/00102202.2021.2006191. <a href="https://elib.dlr.de/146343/1/Bee%20B%C3%B6rner%20Laminar%20Burning%20Post%20Print%2000102202.2021_Postprint.pdf" target="_blank">https://elib.dlr.de/146343/1/Bee%20B%C3%B6rner%20Laminar%20Burning%20Post%20Print%2000102202.2021_Postprint.pdf</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>"Gases - Explosion and Flammability Concentration Limits". <a href="https://www.engineeringtoolbox.com/explosive-concentration-limits-d_423.html" target="_blank">https://www.engineeringtoolbox.com/explosive-concentration-limits-d_423.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"Current Intelligence Bulletin #66: Derivation of Immediately Dangerous to Life or Health (IDLH) Values" (PDF). The National Institute for Occupational Safety and Health (NIOSH). November 2013. 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