I must say that the melting point of copper is 1,983 °F (higher than brass). The highest temperature one can achieve with a butane torch is 3,578 °F but the lowest temperature at which butane ignites spontaneously is 932 °F. Plus, if the copper is thick enough, heat will be diffused through conduction at a pretty efficient level. Another point I'd like to make is that when one smokes, the lighter flame comes in contact with herb, not metal. Herb burns at between 662°F and 1292 °F according to some sources that I'm unsure about. Even if it touches the metal, it's for a time no longer than 12 seconds unless you're totally nuts.
I'd say it's very safe in urgent situations but glass is the preferred choice.