Document qaD3e67R5YeRVjjZ50zJVoE4R

524 0. W. JONES II. Ignition Temperatures Before an explosive mixture can propagate flame a portion of the mixture, must be heated to its ignition temperature. The ignition temperature may be1 defined as the minimum temperature at which rapid combustion becomes inde pendent of external supplies of heat. This implies that in order to initiate flame a definite minimum volume of the gaseous mixture must be heated to its ignitioiij temperature and held at this temperature for a sufficient time to enable flame to?) propagate away from the ignition source. The time period at the ignition tem^f perature necessary to cause the propagation of flame varies over wide limits.'.! For a gas such as hydrogen the time period, or so-called "lag," may be only; a fraction of a second, while for ethane the time period may be 100 seconds or-', longer. It is therefore apparent that, although the temperature at which a given# mixture will ignite and burst into flame is very important, the "lag" at the ! ignition temperature also must be considered, because it often happens that an ignition source may be adequate as far as the temperature- is concerned, yeti the duration is so short that the ignition source is incapable of initiating a self** propagating flame and the mixture fails to ignite. A. FACTORS AFFECTING IGNITION TEMPERATURE The investigation of ignition temperatures is extremely complicated, air the results obtained by various investigators may show wide disagreement becaus of different experimental conditions. Some of the major factors that affect ignition temperatures- arer-the-percentage of -combustible-in " the_mktureT't1 "lag," or time required at a given temperature to cause ignition; the percental of oxygen present; the size, shape, and composition of the apparatus used; i pressure on the experimental mixture at the time of ignition; and the presence,* absence of impurities and catalysts in the mixture. On the basis of the above discussion it becomes apparent that the ter' "ignition temperature" is not a true physica]y.constant, and reported values Jt a given combustible may vary widely. "J. Yeaw, Ind. Eng. Chem., 21, 1030 (1929). "E. Jones, J. Soc. Chem. Ind. (London), 68, 117 (1949). MH. Le Chatelier, Compt. rend., 121, 1144 (1895). . -?AE. .IecresrJ..-GasbeIeuc)it.,.63,-836-(-192J). .................................. "J. RbszlbifSlSi, J. Oasbileucht., 227524 (1890). "G. W. Jones';-R. E. Kennedy, and G. J. Thomas, V. S. Bur. Mines Kept. Invest'. 3589, 1941. " G. Pannetier and P. Laffitte, Compt. rend., 221, 553 (1945). G. W'-Jones,.R,E. Kennedy, and G, J. -Thomas, U. S. Bur. Mines Tech. Paper Noc-fi -1943" * J. Drop, Rec. trav. chim., 56, 71 (1937). G. W. Jones, R. E. Kennedy, and F. E. Scott, V. S. Bur. Mines Repi. Invest. No. 1943. 71G. W. Jones and R. E. Kennedy, Current Researches Anesthesia and Analgesia, 9* (1930). 1G. W. Jones and G. S. Scott, U. S. Bur. Mines Rept. Invest. No. 3666, 1942 HAZARDS OF COMBUSTIBLE GASES AND VAPORS 525 B. MINIMUM IGNITION TEMPERATURES ,OF GASES AND VAPORS The values tabulated in Table 3 may be termed minimum ignition temperares of gases and vapors in air. In those instances where numerous values have TABLE 3 inimum Ignition Temperatures and Flash Points of Combustible Liquids, Gases, and Vapors Ignition temperatures Flash points Name etal eetaldehyde itanilide ,ic acid cetic anhydride sKtone 'Acetophenone Acetyl acetone tyl chloride tylene lein cnylonitrile jic acid ,1; alcohol 'lamina..------ffibromide `^Chloride yodiphenyl monla miayml`ay,cl eatcaet.etat.e Jyljalcohol (Ssoamyl alcohol rAmyl alcohol .ylbenzeno lylchloride fSspiyl chloride jlne.fn and /?) IP- .~... _iyl ether -T nitrate ^j^jaitrite )l*.p_ropipnate Formula C,H,,0, C.H.0 C.H.NO C.H.O. CAOl C,H,0 C.H.0 CjHiO* C,H,OCl C.H, C,H,0 C.H.N C|HioO< C.H.O, C,H,0 _C,H,N_ C,HBr C.H.C1 CuH.iN NH, C,H..O, CjHi.O, CjHjiO CjHijO C|HhO CuHu C,H,,C1 c.h,,ci . QiSw__ CioHuO CioHnO C,H.,NO, C,HuNO. CHio C,H,0 CJS. CrHeOi CoHioOi O 446 349 1017 1022 738 1042 1060 644 734 581 453 898 792 478 712 .705. 583 909 846 1204 676 680 572 657 819 491* 498 649 524 340 802 381 408 712 1004 378 1044 1064 860 C. 230 176 547 550 392 561 571 340 390 305 234 481 422 248 378 374 295 487 452 651 358 360 300 347 437 255* 259 343 273 171 428 194 209 378 540 192 562 573 460 Ref. no. 73 74 75 73 76 77 75 75 75 78 30 47 75 75 80 30... 30 73 75 81 10 21 75 75 76 82 73 30 42 75 83 38 75 75 75 32 75 73 80 Ref. 0 F. * C. no. 97 -36 345 104 127 0 221 174 40 -- <0 23 385 181 72 -- -- -25 ' -- -- 77 77 100 109 67 150 55 10 0 135 -- -- -- 106 250 148 12 250 216 37 -38 174 40 53 -18 105 79 4 -- <-18 -5 196 83 22 -- -- -32 -- -- 25 25 38 42 19 66 13 -12 -18 67 -- -- . --- 41 7ft 121 64 -11 121 102. 10 11 11 11 32 11 11 11 11 79 10 11 11 10 79 32 11 32 11 11 11 11 31 11 11 11 11 11 ,32 11 84 a 11 (continued)