I happened to be working on a couple of enclosures yesterday and recalled the news report talking about how easily the egg-crate foam sound insulation burned at the Club last week.
I had a bunch of scraps of some egg-crate foam left over and so I thought I would conduct an experiment to see just how easy they were to ignite. I was really surprised how fast they went up. When you hold it in a vertical position they really take off.
I know I won't be letting this stuff just lay around my shop anymore.
I'm also giving second thoughts to some of the sound control projects I had in mind for the egg-crate. Like in- line sound baffles for the HVAC and lining cabinet recesses (for speakers).
As you have pointed out the egg crate foam is a fire hazard, so you don't want to use it around audio and video components which all too often put out their own fair share of heat. Find something else which is more flame retardant.
You mean you don't remember me? Back 1999 - 2003, I started and moderated the online-shashki Tweaks forum and also the online-shashki Special Guests forum.
No doubt soundproofing foam is against all fire codes, no matter what part of the country, for public venues. auralex.com has some pdf files regarding their testing procudures, their ignition time, fire spread time, CA Fire code approval, etc ... some interesting reading.
The toxicity of the fumes is another matter. The Class B is a flame retardancy rating. For in -home, or recording studio use (which is the market for these acoustic foam manufacturers) is where the rating applies. They are not stating the foam will not burn. If one puts flooring carpet on his walls for acoustical treatment, the same hazards apply, the same disclaimers apply. All these materials come with their own risks when fire is present.
And of course, as soon as you mount anything vertically, as on a wall, any flame/heat source will tend to propagate far more quickly due to convection carrying heat upwards to cover a greater area (while simultaneously replenishing oxygen into the source)... a far cry from a cinder lying on a carpet which tends to affect only its immediate area as it smolders.