(S (S (S (BASENP (DT A) (NNP Tesoro) (NNP Corp.) (NN refinery)) (VP (VP (VBD caught) (BASENP (NN fire))) (PP (IN at) (NP (NP (BASENP (RB about) (NN 0030)) (BASENP (JJ local) (NN time))) (PRN (LRB -LRB-) (NP (BASENP (NN 0830)) (BASENP (NN GMT))) (RRB -RRB-)))))) (SBAR (IN while) (S (BASENP (NN maintenance) (NN work)) (VP (VBD was) (VP (VBG being) (VP (VBN performed) (PP (IN in) (NP (BASENP (NN preparation)) (PP (IN for) (S (VP (VP (VP (VBG returning) (NP (BASENP (DT a) (NN part)) (PP (IN of) (BASENP (DT the) (NN plant))))) (PP (TO to) (BASENP (NN operation)))) (PP (IN in) (NP (BASENP (DT a) (JJ dangerous) (NN procedure)) (VP (VBG involving) (S (VP (VP (VBG increasing) (BASENP (NN heat) (CC and) (NN pressure))) (PP (IN in) (NP (BASENP (DT the) (NN unit)) (VP (VBN involved)))))))))))))))))))) (PERIOD .))