Combustion ( old ) < onlyinclude > < / onlyinclude > Combustion is a mage ability that when activated , gives increasing critical strike chance with Fire spells until 3 criticals occur . Each time a fire spell is cast , the chance to get a critical strike with fire is increased by 10 % . This effectively guarantees at least 3 critical strikes from Fire spells within the next 13 casts . This ability is talent trained , requiring 31 points in the fire tree , making it popular with fire mages . Activating this ability does not invoke the global cooldown , as such it can precede a spell , often with other non - GC abilities such as trinkets , as part of a macro . The cooldown of Combustion does not start until after all charges have been expended . It is very valuable when intelligently coupled with the Fire talent Hot Streak . Measuring the value of the talent . Combustion is a means to increase damage , but compared to other damage - boosting abilities ( like for example arcane power ) , the payoff is indirect and its value harder to quantify . Firstly , combustion is a delayed effect . The first shot sees no benefit at all , and there is no " guaranteed " benefit until the cumulative crit % reaches 100 , forcing a crit on the remaining charges . Combustion ' s " sweet spot " lies somewhere after the talent has had a chance to build up some , but before its charges are spent . This sweet spot varies according to the underlying stats of the mage . Combustion " peaks " sooner on a high - crit mage than a low - crit mage . Secondly , the total value of the payoff is variable and depends on the underlying stats of the mage - - and in more ways than one . Consider for example the extreme cases : a hypothetical mage with zero base crit chance would get 3 crits from the talent every time . A hypothetical mage with 100 % base crit chance would see no benefit from activating the talent . These edge cases clearly demonstrate the existence of a gradient in the talent ' s potency . But the gradient is not linear ; natural crits not only reduce the value of artificial crits ( " I would have crit anyway " ) , they also waste " charges " on the talent . The more natural crit a mage has , the less total payoff they can expect to see . So a mage with 50 % crit gets substantially less than 50 % of the maximum benefit . So what exactly is the value of combustion ? How does it compare to other boosters ? Say for example a fire mage anticipated the need for burst damage in an upcoming fight , and wanted to maximize the leverage of combustion as a " mini arcane power " by skewing his nominal gear selection to intentionally suppress crit in favor of damage . Obviously there would be a difference , but would the difference be significant or trivial ? At what point would the reduction in sustainable baseline dps negate the improved burst coefficient ? In order for the mage to find his prefered balance of burst vs sustainable dps , we need some numbers . The following two graphs were obtained by writing a simple script that mimicks the ruleset of combustion - - namely : The script was run 50 , 000 iterations , and recorded the average damage of each cast in the sequence . The test was repeated at various levels of base crit , from 0 % to 50 % . The first graph is raw data . The X axis is casts ( which can be interpreted as " time " ) . The Y axis is how much damage this spell did , on average , relative to the same spell cast without the combustion talent . Arcane power is also graphed as a reference curve . For the sake of argument , AP is assumed to last for 5 casts since we ' re comparing fireballs . It does not account for other ways an arc mage could pack more hits into his boost duration , like pompyro or icy veins . If you want to assume more or fewer hits during AP , simply shift the curve right or left correspondingly . Also keep in mind the graph does not factor in other differences in talents etc . It ' s intentionally as abstract as possible , rating each talent only in terms of how it modifies the baseline damage of the mage who uses it . Two things are immediately obvious : as expected , AP is very strong from the start , but also - - perhaps surprisingly - - " for mages with low crit there ' s a brief period where combustion is ( on average ) an even stronger boost than AP " , once it ' s had a few shots to wind up and accrue a decent crit bonus . Of course , by this point AP has already been running strong for a while , and already raked in most of its total effect . In order to grade Combustion fairly as a boost , we probably ought to measure the " total " damage delivered , starting from the first cast ( again , measured relative to the damage that would be delivered regardless of the talent ) . Thus the following graph : Some observations : Combustion is nothing compared to AP during the first 15 seconds . However in the time period immediately following , Combustion catches up impressively . A mage with 20 % crit or lower actually gets more total damage increase from Combustion than AP , if the fight lasts long enough for him to catch up . He catches up around cast # 8 ( 24 sec ) , where the deep purple band overtakes the red line . A mage with 20 % crit can think of Combustion as a 20 % boost over 21 seconds casting fireball . A crit - heavy mage approaching 50 % can think of Combustion as a 10 % boost over 15 seconds , which still isn ' t half bad . Since the horizontal axis is Casts and not Time , the Combustion graph stays the same whether you ' re casting Fireball or Scorch . But if you wanted to compare against AP using scorch , you ' d need to imagine keeping the red line constant while compressing the rest of the graph horizontally by half . The Combustion scorchist will accelerate through the ranks of combustion faster than his fireball cousin , resulting in an earlier peak , but the combustion scorchist will also run out of charges even sooner , reducing the total value - over - time of his Combustion compared to a fixed - duration boost like AP .