The lower jaw is hollow, to support the breath weapon, but the upper also has a weapon pocket. Each gland secretes a chemical that reacts with the other - the upper secretes a magnesium-rich oil that is replenished by the consumption of rocks in the mountains, while the lower secretes an aqueous enzyme solution similar to mammal saliva. The drake sprays both compounds into the air using special teeth on the palate and mouth floor, and as they combine, the magnesium is released and ignites - resulting in a blast of flames that can reach up to 10,000 degrees Farenheit. To withstand the heat, the tissues have an asbestos-like compound that is concentrated in the scales, allowing the drake to withstand this high temperature. It cannot be burned by its own fire breath. Even if the mechanism backfires, the internal burns are only rarely fatal, as there is no need for a gas supply inside the body. This drake uses its flame breath as a display, to cook its meals, and to fight with rivals and enemies - it does not need to kill with the flame breath because its bite does the job easily.What material can my biological version asbestos made of ? What might be chemical composition of it ? Note: magic is not allowed in my franchise
If you're going to have an asbestos-like compound, why not just use asbestos? Chrysotile, the most common form of asbestos, is a magnesium-rich mineral, naturally occurring, and is obviously fire-resistant. The breakdown of asbestos can lead to the formation of highly reactive magnesium compounds. With a biology specifically designed around processing the mineral, this could be both the source of your heat shield, and also the source of your magnesium. Biology adapted to asbestos will also presumably be resistant to the toxic and harmful effects of the mineral.
- PS If the fire is used to cook food, I'd guess that you'd only use it to ignite your fire, not for the actual cooking. The production of your oil is likely quite energy-intense, and the gain in caloric value from cooking is probably a lot less than the cost to make the oil.