open flame
/ˌəʊp(ə)n ˈfleɪm/noun
1A state of combustion in which a flame is visible (as opposed to smouldering or glowing). Chiefly figurative or in figurative contexts: unconcealed and unrestrained passion, enmity, thoughts, etc. Frequently in to burst into (an) open flame and variants.
2A naked flame.
Origin
Late 16th century; earliest use found in Brian Melbancke (d. 1600), writer. From open + flame adjective.