Explore all of ul.com

What appears to be several dozen or more glass candles fill the approximately 12 X 15 room. Overseeing the testing of candles, which come in an endless variety of sizes, shapes and scents, is not for the migraine prone. Luckily for the woman monitoring the room, the starkness of the space and its competing odors do not seem to bother her senses.

And, that’s a good thing for Amanda Jackson, a lab technician at UL’s consumer hardline lab in Bentonville, Ark. who carefully monitors the burn performance of an assortment of candles each work day.

During the burning process, the candles burn in cycles, four-hours of burning combined with one hour cool down, per cycle. Following the cool down period, Jackson trims each wick down to ¼ of an inch to get them ready for their next light.

Each candle undergoes a test to measure the amount of soot released during a burn cycle. Soot occurs when a candle’s material-wax, fragrance, wick- burn inefficiently because the combustion of the materials is incomplete.

To determine the amount of soot produced by a candle, the product to be tested is placed inside a wire mesh cylinder, called a soot machine. The candle is lit and allowed to burn for five minutes before a clear piece of heat-resistant glass is placed 180 mm (7.1 inches) above the base of the candle. The glass will capture any residual soot given off during the four-hour burn process. Jackson will then compare the amount of soot captured against a clear piece of glass.

In addition to the soot test, Jackson continuously monitors the candle to make sure the wick remains centered. A misplaced wick will cause the candle to burn unevenly with excessive soot build-up on the sides of the glass. If left to its slow meander, the glass can get too hot and crack or shatter. At best, this is a mess to clean up, but it also constitutes a safety hazard as the hot wax could burn someone or catch surrounding materials on fire.

Jackson also measures the height of the flame every hour to ensure it does not exceed three inches. A flame that gets out of control is also a fire hazard, reinforcing the warning never to let a candle burn unattended.
Finally, wax pillar candles are evaluated to make sure there isn’t any spillage during the burn process.

All candles are allowed to burn to their end of life, which is when it self-extinguishes or is fully consumed. End of life can be premature, or it can be after the candle is fully consumed.
The National Candle Association offers safety tips to help make each candle burn a safe experience.

UL experts provide regular contribution to blogs of interest to the Consumer and Retail Services community.  Join the discussion and learn from your peers.