(S (S (S (VP (VBG Describing) (SBAR (WHADVP (WRB how)) (S (NP (BASENP (DT the) (NN explosion)) (PRN (COMMA ,) (SBAR (WHNP (WDT which)) (S (VP (VBD killed) (BASENP (NN eleven) (NN rig) (NNS personnel))))) (COMMA ,))) (VP (VBD occurred)))))) (COMMA ,) (S (BASENP (DT the) (NN report)) (VP (VBZ states) (SBAR (IN that) (S (QT (DQL ``) (QTC (S (NP (NP (BASENP (DT the) (NN heating)) (COMMA ,) (BASENP (NN ventilation))) (CC and) (BASENP (NN air) (NN conditioning) (NN system))) (VP (ADVP (RB probably)) (VP (VP (VBD transferred) (BASENP (DT a) (JJ gas-rich) (NN mixture))) (PP (IN into) (BASENP (DT the) (NN engine) (NNS rooms)))))) (COMMA ,)) (DQR '')) (SBAR (WHADVP (WRB where)) (S (S (BASENP (DT the) (NNS hydrocarbons)) (VP (VBD ignited))) (CC and) (S (BASENP (DT a) (NN fireball)) (VP (VBD engulfed) (BASENP (DT the) (NN rig))))))))))) (PERIOD .))