Which type of fire extinguisher is required in the machinery space of vessels over a certain size with certain horsepower?

The requirement for a fire extinguisher in the machinery space of vessels over a certain size and horsepower is based on specific safety regulations to ensure effective fire protection. The correct choice, a B-II fire extinguisher, is specifically designed to handle flammable liquid fires, which are commonly associated with machinery spaces due to the presence of fuels and lubricants.

B-II extinguishers are rated to combat Class B fires, which involve flammable liquids, while they may also be effective against electrical fires when the live equipment can be de-energized. The size and design of these extinguishers provide a suitable volume of extinguishing agent, ensuring that operators have adequate equipment to manage and extinguish fires that could pose serious safety risks.

The other options represent different classes and ratings of fire extinguishers which do not meet the specific requirements for addressing the most common fire hazards found in machinery spaces. Therefore, B-II is the appropriate standard for this scenario, ensuring compliance with maritime safety regulations and protection against potential fire hazards in critical areas of the vessel.