No possible doubt about this : manufacturing candles that do not constitute a fire hazard in normal usage conditions should be at the source of your concerns. But when talking about candles, there is another very sensitive issue that regularly makes the headlines and worries consumers and manufacturers alike: the release of soot by burning candles.
If you've read the article titled How do candles work?, you probably remember that by-products of candle combustion are water, carbon monoxide and dioxide and... soot. How much soot a candle produces depends on several factors: type of wax used, amount and type of fragrance oil and, above all, the choice of the right (type and size) wick.
An unsuitable wick or one that is not properly maintained by the consumer (trimmed to about 1 cm before every lighting of the candle) will for sure produce too large an amount of soot that sooner or later will build up on the walls, the ceilings and pretty much everything in the room where candles are burnt. Soot built-ups create damages that are notoriously difficult to repair. Several lawsuits relating to damages caused by candle soot built-up have been filed in the United States and the United Kingdom in recent years.
To keep damages caused by candle soot to homes and to the health of their residents to a minimum, the EN 15426 standard (European Union) and the ASTM F2326 standard (United States) suggest a standard test protocol that allows manufacturers to measure the amount of soot emissions.
The test involves burning the candle inside a wire mesh cylinder on top of which a heat resistant glass plate is mounted to capture the released soot. At the end of the test, the glass plate will be placed between a light source and a photometer to measure what amount of light passes through the soot covered plate. That amount of light gives an indication of the amount of soot released during the test.
Depending on the type of candle (container candle or not) and its size, the test consists of one to three burning cycles, as explained below.
A single continuous burning cycle ending when the residual height reaches 10 mm.
A single continuous burning cycle ending when the candle self extinguishes.
Two burning cycles.
Two burning cycles.
Three burning cycles.
After the glass plates have been analyzed with the photometer, an average is computed if more than one burning cycle were performed. The soot index is then known. The standard requires that the average is not superior to 1.0 per hour and that no burning cycle (if more than one) shows an index higher than 2.0 per hour. A candle whose test results exceed these values does not meet the terms and conditions of the standard.