Rick, whenever the dealer installing my wall plates stopped by the house to check out my in wall wiring/cabling job the first thing he did was grab one of the speaker wires and said 'Uh oh ... you should have used oxygen free, in-wall specific speaker wire' 'Oh really? And why is that?' 'Well oxygen free is better cable and specific in wall wires have an outer liner that will not produce fumes if ever caught on fire'.
After a couple of minutes of 'real talk' he finally confessed that what I installed would be perfectly fine, although maybe not politically correct for the industry and 'there's really not any difference between oxygen free and regular wire'. As for the fumes I did address that if the these particular wires were on fire the least of my worries was the fumes produced by the plastic sheathing on a 12 gauge speaker wire. He wholeheartedly agreed.
