Mark,
Since I used to be employed (by UL) as a Product Safety Engineer, I figure I should do some additional research on the fire extinguisher question. So, here is some more info:
Portable Halon extinguishers apparently are no longer Listed (Ozone depletion issues). It appears that the replacement if you don't want the normal dry chemical type is called "clean agent". Here is a link from one of the major manufacturers that gives some information:
http://www.ansul.com/fireprotection/Pro ... /F9721.pdf
Here is a link to their dry chemical and their CO2 portable units.
http://www.ansul.com/fireprotection/Pro ... f94126.pdf
I suspect that a Listed Clean Agent portable extinguisher will be pricey. For normal car use, dry chemical from Home Depot, etc. is common. CO2 extinguishers may be available and less pricey than clean agent.