Question 932 Deck Safety

The correct answer is B) completely closed. When the mainline valve of a self-contained breathing apparatus (SCBA) is open, the bypass valve should be completely closed. This is because the bypass valve is designed to provide an alternate air supply in case of a malfunction with the mainline valve. With the mainline valve open, the SCBA is functioning normally, and the bypass valve should be kept closed to prevent any unnecessary air loss or disruption to the primary air supply. The other options are incorrect because: A) partially opening the bypass valve would allow air leakage, which is undesirable; C) completely opening the bypass valve would divert air away from the mainline, disrupting the normal operation of the SCBA; and D) disconnecting the bypass valve would render the SCBA's backup air supply inoperable, which is not recommended.