Final answer:
To safely extinguish a fully involved fire in a CNG or LPG fueled vehicle, Dry Chemical Powder is the recommended extinguishing agent as it interrupts the chemical reaction of the fire.
Step-by-step explanation:
When dealing with a vehicle fueled by CNG (Compressed Natural Gas) or LPG (Liquefied Petroleum Gas) that is fully involved in a fire, the safest way to fight the fire is using Dry Chemical Powder. This type of extinguishing agent works by interrupting the chemical reaction of the fire triangle (fuel, heat, and oxygen). Water can be ineffective and dangerous as it may spread the fuel, while CO₂ might not be sufficient for a fully-involved vehicle fire. A fluorinated foam solution is effective for fires involving organic liquids but might not be the best option for pressurized gases like CNG or LPG. Furthermore, compounds such as carbon tetrachloride are not used in fire extinguishers due to the toxic gas formation, like phosgene. The choice of extinguishing agent is critical for safety and the effectiveness of firefighting efforts.