It is critical that your space is air-tight, has enough oxygen for the occupants, and is very well-insulated. According to USFS National Technology and Development, wildland fires are typically 1,600 degrees Fahrenheit and sometimes reach 2,000 degrees or more. Humans can tolerate 300 degrees Fahrenheit for a brief time and 250 degrees Fahrenheit for an extended period. Underground bunkers offer the greatest protection from heat exposure of an intense fire.