, ▁and ▁is ▁able ▁to ▁sust ain ▁a ▁rate ▁of ▁rapid ▁ox id ation ▁that ▁produces ▁a ▁chain ▁reaction . ▁This ▁is ▁commonly ▁called ▁the ▁fire ▁t etra hed ron . ▁Fire ▁cannot ▁exist ▁without ▁all ▁of ▁these ▁elements ▁in ▁place ▁and ▁in ▁the ▁right ▁proport ions . ▁For ▁example , ▁a ▁fl amm able ▁liquid ▁will ▁start ▁burning ▁only ▁if ▁the ▁fuel ▁and ▁o xygen ▁are ▁in ▁the ▁right ▁proport ions . ▁Some ▁fuel - ox y gen ▁mix es ▁may ▁require ▁a ▁catal yst , ▁a ▁subst ance ▁that ▁is ▁not ▁consum ed , ▁when ▁added , ▁in ▁any ▁chemical ▁reaction ▁during ▁comb ust ion , ▁but ▁which ▁enables ▁the ▁react ants ▁to ▁comb ust ▁more ▁readily . ▁ ▁Once ▁ign ited , ▁a ▁chain ▁reaction ▁must ▁take ▁place ▁where by ▁fires ▁can ▁sust ain ▁their ▁own ▁heat ▁by ▁the ▁further ▁release ▁of ▁heat ▁energy ▁in ▁the ▁process ▁of ▁comb ust ion ▁and ▁may ▁propag ate , ▁provided ▁there ▁is ▁a ▁continuous ▁supply ▁of ▁an ▁ox id izer ▁and ▁fuel . ▁ ▁If ▁the ▁ox id izer ▁is ▁o xygen ▁from ▁the ▁surrounding ▁air , ▁the ▁presence ▁of ▁a ▁force ▁of ▁gravity , ▁or ▁of ▁some ▁similar ▁force ▁caused ▁by ▁acceleration , ▁is ▁necessary ▁to ▁produce ▁con ve ction , ▁which ▁removes ▁comb ust ion ▁products ▁and ▁brings ▁a ▁supply ▁of ▁o xygen ▁to ▁the ▁fire . ▁Without ▁gravity , ▁a ▁fire ▁rapidly ▁surr ounds ▁itself ▁with ▁its ▁own ▁comb ust ion ▁products ▁and ▁non - ox id izing ▁g ases