Naked flames, open flames in US usage, are lit candles, tea lights and torches. With flowers they create the evening light, but they are also the first rule to check: many historic villas ban them, others accept them only in enclosed glass holders, others only as LED candles. The decision lies with the venue, not the flower designer.
The practical rule: no flower, leaf or ribbon above or near a flame, and dry materials such as pampas grass and dried flowers well away. Outdoors, wind increases the risk. The guide on flowers and candles covers holders, distances and alternatives; the one on lighting and flowers covers lighting; the one on flowers, caterer and venue tells you who decides.
What to ask the venue: whether candles are allowed, in which holders, and who lights and puts them out.
