I did a retreat several years ago at a center where open flames weren't permitted, so we used battery-powered tealights instead and I've never gone back to candles since then. That center director's concerns were well-founded, too, because I can think of several retreat cabins at various locations in the US and Canada that have burned down because of someone's carelessness with candles or incense. I'm just sayin'...
"All the sublime teachings, so profound--to throw away one and then grab yet another will not bear even a single fruit. Persevere, therefore, in simply one."
--Dudjom Rinpoche, "Nectar for the Hearts of Fortunate Disciples. Song No. 8"