Combustible gas indicators measure the presence of combustible gas as a percentage of the（）.

单项选择题CO2 extinguishes a fire by（）.

A.cooling
B.smothering
C.chemical action
D.All of the above

单项选择题Cargo transfer operations on a tanker need NOT be stopped when（）.

A.a tug comes alongside while the tanker is loading grade D and E cargoes
B.a large，fresh oil spill is discovered immediately adjacent to the side of the tanker
C.there is an electrical storm in the vicinity
D.there is a fire on the dock or on a nearby vessel

单项选择题Blocking open or removing fire dampers can cause（）.

A.fixed foam systems to be ineffective
B.faster cooling of the fire
C.the accumulation of explosive gases
D.the fire to spread through the ventilation system

单项选择题Before using a fixed CO2 system to fight an engine room fire，you must（）.

A.secure the engine room ventilation
B.secure the machinery in the engine room
C.evacuate all engine room personnel
D.All of the above

单项选择题Before a tank is to be crude oil washed，the oxygen content in the tank must be measured at a position（）.

A.immediately above the level of the oil
B.at the top of the tank
C.in the vent riser
D.one meter from the deck