In a third-degree burn, all the layers of the skin are burned. Third-degree burns can be deadly if the majority of your body is burned. Third-degree burns may require skin grafting or plastic surgery. This is generally required because new skin will not grow in the third-degree burn area.
Seek medical attention immediately, if you or someone you love has a third-degree burn. The National Institutes of Health recommend calling 911 if you have the following burn issues:
• The burn is severe (third degree)
• The burn is extensive (the size of your palm or larger)
• The person shows signs of shock
• You aren't sure how serious it is
• The burn is caused by chemicals or electricity
• Physical abuse is the known or suspected cause of the burn
• The person inhaled smoke
• There are other symptoms associated with the burns
One symptom of third-degree burns is a lack of pain.
https://www.empowher.com/burns/content/first-aid-third-degree-burns