A burning candle is a controlled system of combustion where heat is distributed across two vastly different areas: the pool of liquid fuel surrounding the wick and the much hotter, active flame itself. Understanding the temperature dynamics of these components is important for appreciating the science behind a candle’s operation. The heat level in each area is regulated by different physical and chemical processes, resulting in a wide variation from mild warmth to extreme combustion temperatures.
The Temperature of the Melted Wax Pool
The liquid wax pool, or melt pool, maintains a relatively consistent temperature closely linked to the wax’s melting point. For common candle waxes, this temperature typically falls between 120°F and 160°F (49°C to 71°C). This temperature is regulated by thermal equilibrium, where the heat supplied by the flame is balanced by the continuous consumption of the liquid wax. As the wick draws up and vaporizes the molten wax, it prevents the temperature from climbing uncontrollably.
The pool’s temperature remains just above the melting point of the wax blend, ensuring the fuel remains liquid and can be drawn into the wick via capillary action. If the temperature rose significantly higher, the wax would vaporize too quickly, resulting in a larger, unstable flame. This consistency allows the candle to burn steadily over an extended period.
Understanding the Candle Flame’s Heat
The temperature of the actual candle flame is vastly higher than the melted wax pool, reflecting the energy released during the combustion of the vaporized wax. A candle flame is not uniformly hot but is composed of distinct zones, each with a different temperature profile. The innermost zone, closest to the wick, is the coolest, containing unburned wax vapor and registering temperatures around 600°C to 800°C (1,112°F to 1,472°F). This dark zone lacks sufficient oxygen for complete burning.
Moving outward, the middle zone is the brightest and most visible part of the flame, glowing yellow due to the incandescence of hot, uncombusted carbon particles. This area operates at a higher temperature, typically between 1,000°C and 1,200°C (1,832°F to 2,192°F). The hottest part of the flame is the non-luminous, faint blue outer edge, where the vaporized wax mixes with atmospheric oxygen for complete combustion. This outer region can reach temperatures exceeding 1,400°C (2,550°F).
Factors Influencing Wax Temperature
The specific blend of wax largely determines the baseline temperature of the melt pool due to variations in melting points. Natural waxes, such as soy, typically have a lower melting point than paraffin-based waxes, resulting in a comparatively lower melt pool temperature. Conversely, beeswax has a high melting point, requiring the melt pool to achieve a higher temperature to remain liquid. Adding fragrance oils can also slightly reduce the wax’s melting point, influencing the pool’s equilibrium temperature.
The size and material of the wick also play a significant role in heat transfer and wax temperature. A thicker or more efficient wick draws up and consumes more fuel, generating a larger flame and potentially increasing the size and depth of the melt pool. Furthermore, the container material affects heat dissipation; glass and ceramic containers retain heat differently than metal, influencing the temperature of the wax pool, especially near the container walls.
Safety and Burn Risk Assessment
The temperatures achieved by a burning candle present two primary safety concerns: contact burns from the liquid wax and fire risk from the open flame. Although relatively cool compared to the flame, the melted wax pool is still hot enough to cause serious skin injury. Exposure to liquid at temperatures between 120°F and 160°F (49°C to 71°C) can result in first- or second-degree burns. For instance, a second-degree burn can occur in as little as three seconds of contact with liquid at 140°F.
The flame itself poses a direct fire hazard, making proper clearance from combustible materials necessary. Beyond the immediate danger of the flame, the wax itself can ignite if overheated, an event called a flashpoint. For common waxes, this flashpoint is far above the melt pool temperature, often ranging from 350°F to over 450°F (177°C to 232°C). While the wick’s action normally prevents the entire pool from reaching this temperature, factors like excessive heat retention or foreign debris can increase the risk of a catastrophic pool fire.