From professional translators, enterprises, web pages and freely available translation repositories.
r15: contact with water liberates extremely flammable gases
r15: 水と接触するときわめて高引火性のガスを放出する。please take the official translations! you find them here: http://europa.eu.int/eur-lex/lex/lexuriserv/lexuriserv.do?uri=celex:32001l0059:en:html
r18: in use, may form flammable/ explosive vapour-air mixture
r18: 使用中に引火性/爆発性の蒸気/空気混合気体を生成する可能性がある。please take the official translations! you find them here: http://europa.eu.int/eur-lex/lex/lexuriserv/lexuriserv.do?uri=celex:32001l0059:en:html