First Aid Exam Taken from the 2017 Northern Regional Contest held in Clymer, New York Progress Indicator: Question 4 of 30 4.  Air locks are to be used by mine rescue teams Choices: in place of a fresh air base when closing a door or building a bulkhead behind which conditions is not definitely known before opening a barricade in bad air behind which trapped miners might be located as refuges where they can remove or repair their breathing apparatus all of the above