Candle flame with zones marked A candle flame has three distinct regions. The innermost zone, directly above the wick contains wax vapors that have just been vaporized. The middle zone, the yellow portion of the flame is an oxygen depleted zone, where partial oxidation has occurred, but insufficient oxygen exists to burn all of the vapors present. The temperature in this region is hotter than the innermost zone, but cooler than the outer zone. The outer zone is the area where the flame is the hottest and the oxidation process is complete.
Hazards : According to the U.S. National Fire Protection Association, candles are one of the leading sources of residential fires the world over. With almost 10% of civilian injuries and 6% of civilian fatalities from fire attributed to candles.
A candle flame that is longer than its laminar smoke point[ : will emit soot. Soot inhalation has known health hazards. Proper wick trimming will substantially reduce soot emissions from most candles.
The liquid wax is hot and can cause skin burns, but the amount and temperature are generally rather limited and the burns are seldom serious. The best way to avoid getting burned from splashed wax is to use a candle snuffer instead of blowing on the flame. A candle snuffer is usually a small metal cup on the end of a long handle. When placed over the flame the oxygen supply is cut off. They were used daily when the candle was the main source of lighting a home, before electric lights were available.
Glass candle holders are sometimes cracked by thermal shock from the candle flame, particularly when the candle burns down to the end. When burning candles in glass holders or jars, users should avoid lighting candles with chipped or cracked containers, and stop use once 1/2 inch or less of wax remains.
A former worry regarding the safety of candles was that a lead core was used in the wicks to keep them upright in container candles. Without a stiff core, the wicks of a container candle could sag and drown in the deep wax pool. Concerns rose that the lead in these wicks would vaporize during the burning process, releasing lead vapors — a known health and developmental hazard. Lead core wicks have been not discontinued the 1970s. Today, most metal-cored wicks use zinc or a zinc alloy, which has become the industry standard. Wicks made from specially treated paper and cotton are also available.