(S (S (S (BASENP (DT The) (NN fire)) (VP (VBD started))) (SBAR (WHADVP (WRB when)) (S (NP (BASENP (NN equipment)) (VP (VBG being) (VP (VBN used) (PP (IN on) (BASENP (DT a) (JJ blocked) (NN water) (NN line)))))) (VP (VBD sparked))))) (PERIOD .))