51. During test and/ or maintenance work of the CO2 system affecting the releasesystem, precautionsto ensure that the gas is not released in the engine roomdue to a mistakeare to be ensured. What precautions should be taken

A. No special precautions necessary
B. The main supply line to be blanked off prior to the work
C. Check the main valve for a potential leakage
D. arrange a watchman in the CO2 central