The human skin is very sensitive to temperature. When the skin temperature reaches 45°C, the person will have a burning feeling. When the temperature reaches 72°C, it will cause second-degree burns to the skin.
Alice Stoll and Maria Chianta in the latter half of 1960s, conducted a series of experiments on live, anesthetized test subjects. They recorded the time required for a given heat source at which the onset of pain occurred, producing minimal blistering within 24 hours. Simply put, the time duration in seconds to produce a second-degree burn was recorded at different heat intensities (heat flux).
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