Name the irritant classified NFPA 704 with the highest enthalpy of vaporization ?
select ?ent where { ?ent wdt:P31 wd:Q6073871 . ?ent wdt:P2116 ?obj . ?ent wdt:P4952 wd:Q51139288 } ORDER BY DESC(?obj)LIMIT 5 
irritant: Q6073871 nfpa 704: standard system for the identification of the hazards of materials for emergency response: Q51139288