What is the most effective way to extinguish a puddle of paint thinner?

The most effective way to extinguish a puddle of paint thinner is to use a Class B fire extinguisher, which is designed for flammable liquids. If a fire is already present, evacuate the area and call emergency services. Avoid using water, as it can spread the flammable liquid. Instead, use dry chemical extinguishing agents or foam to suppress the flames safely.