If there is the opportunity to do so safely, what type of extinguisher should be used to fight an oil-based fire caused by sparks from the derailment?

The appropriate choice for extinguishing an oil-based fire, especially one that may be exacerbated by sparks from a derailment, is indeed CO2 or dry chemical extinguishers. These types of extinguishers are specifically designed to combat flammable liquids, such as oils, by cutting off the oxygen supply and thereby smothering the flames.

CO2 extinguishers work by displacing oxygen around the fire, which is crucial since most fires need oxygen to sustain combustion. They do not leave any residue, making them a good choice for fighting fires involving flammable liquids, and are also effective in enclosed spaces where electrical equipment might be present.

Dry chemical extinguishers, on the other hand, utilize a powder that interrupts the chemical reaction of the fire, effectively extinguishing the flames. They are particularly versatile and can handle various types of fires, including those fueled by flammable liquids.

In contrast, using water on an oil-based fire can be extremely hazardous, as water can cause the oil to spread and worsen the fire instead of extinguishing it. Therefore, having CO2 or dry chemical extinguishers readily available is crucial for ensuring safety in a situation involving oil fires caused by sparks or other ignition sources.