All oil types are included under this symbol including oils that are difficult to recover. This is particularly an issue with old air-conditioning units, domestic refrigerators, old motor vehicle engines, and gearboxes. The symbol also covers the recovery of oils from transformers and all other oil contained in equipment before being transported to the smelter where they are melted in high-temperature furnaces. Often, not all oils are recovered from recyclable materials, burning them causes highly toxic gases that are directly introduced to our atmosphere. Phosgene is a highly toxic and carcinogenic poison that is released when old refrigerator insulation comes in contact with fire.