Halon is for all the world the same as dry cleaning fluid.
dichloro-difluoro-methane chemical Formula C Cl2 F2
Halon is also widely used an a gas anaesthetic. One of the very best. I have been put out on Halon quite recently for an op. Nice sleepy sensation and no hangover.
Using it will CLEAN the insides of the Landy.
Dry powder is sodium bicarbonate - aka baking powder - usually blown out by carbon dioxide gas, and it makes a disastrous mess.
It also sets quite hard over time IN the extinguisher, so y'all out there with Soda-Bic extinguishers should give them a really good shaking on a regular basis. Once you've used one inside a car the car is wrecked, especially if it gets wet.
I carry a red compressed air wet-water extinguisher in the Disco. The water has detergent added (fairy liquid actually) and it puts out all vehicle fires so far pretty smartish. It is also very good at wetting people while you try to hoick them out of burning cars, so they say.
I've used it 5 or 6 times but luckily never had to on my own vehicles.
CharlesY