Step 1: Separate surface safety functions from subsurface reservoir functions:
It helps to first split the four given options into two groups: options that deal with hydrocarbons already at the surface facility, and options that deal with fluid movement inside the reservoir. A platform safety system, by definition, exists to protect people and equipment at the surface, so only the surface related options can be genuine objectives of that system.
Step 2: Place option A in the surface group:
Preventing a leak or overflow of hydrocarbons is a surface containment task handled by pressure relief valves, level alarms, and shutdown valves on the process equipment itself, which clearly falls under the safety system's job, so option A stays in.
Step 3: Place option B in the surface group:
Preventing ignition of hydrocarbons that have already been released is handled by gas detectors, explosion proof equipment, and automatic isolation of electrical sources, again a surface facility function aimed at stopping a fire or explosion, so option B stays in.
Step 4: Place option C in the reservoir group and exclude it:
Water coning is governed by the pressure drawdown applied at the perforations and the mobility contrast between oil and water in the reservoir, and it is controlled by reservoir engineers through production rate and completion design, not by any platform level safety device, so option C is excluded.
Step 5: Place option D in the reservoir group and exclude it:
Gas coning is likewise governed by drawdown and the position of the gas oil contact relative to the perforations, again a reservoir management concern rather than a platform safety concern, so option D is excluded.
Final Answer:
\[ \boxed{\text{A and B are the objectives of the platform safety system}} \]