Seriously.
Colin the Pilot--I direct your attention to the rest of the paragraph.
In any of these instances, USE EYE/EAR/HAND PROTECTION, keep pets and kids away, do all the normal safety things.
If it was me using the fire method, I'd toss the cases/primers in question into the fire, one at a time, making sure each goes pop before tossing in the next one. Not all at once, for heavens' sake--you'd scatter burning embers all over your back yard! Also, you wouldn't be certain that every single primer had been ignited. I certainly WOULD NOT do it in the fireplace inside the house!!
A perhaps safer fire-for-killing-primers method has been suggested: Dig a hole mebbe 18" deep, put glowing charcoal in the bottom, toss the primers in one by one.
The 2 things that reliably kill primers are (1) percussion, and (2) heat.
My own preferred way is to hit 'em with a hammer. Again, you use ear/eye/hand protection.
If the primers have been removed from the cases, put one primer on large rock, hit it with hammer. Repeat until all primers are done. It takes a pretty firm blow with the hammer to set 'em off. Noisy but effective.
If the primers are still in the cases I clamp one case, mouth downward, in a vise and put a nailset on the primer, then hit the nailset with a hammer. The nailset acts just like a gun's firing pin. Repeat until all primers are done. You could use a spike with the tip ground down I suppose. Again, noisy but effective. Doing this the first time, I was surprised at the primer flame coming out of the case mouth. Having seen that, I quit worrying about when firing a cartridge in a gun, getting all the powder lit up, fer sure!
With any of these methods, killing primers is at best a noisy hassle, best avoided.