I believe if one is truly concerned about a fire in a car you need to get an on board fire suppression system. Having had the need to deploy one myself trust me you wont be wanting to fumble around with finding and deploying any type of extinguisher. These days you can by systems that self deploy as well. if you really are concerned about it buy the right stuff, and yes Halon works it does displace oxygen for a FEW SECONDS, I have deployed a system twice only ill affect had was a small burn on my ankle. If you are that concenred here is a NON halon system that self deploys if it senses 175 degrees or can be manually deployed.

https://www.leafspringnation.com/co...-autosense-fireade-fire-system-automatic