Is it safe to burn iron ore with a depth of 100 m in the absence of oxygen?

Not safe. In iron ore with a depth of 100 m, it is unsafe to use hot work under the condition of lack of oxygen, because the iron ore itself contains some flammable substances, such as sulfide. If oxygen is insufficient, these substances will spontaneously ignite and lead to fire, while in the case of lack of oxygen, hot work will produce a lot of toxic gases such as carbon monoxide. If it cannot be discharged in time or is poorly ventilated, these gases may cause harm to human body, even lead to poisoning, suffocation and other accidents, so it is unsafe.