Howard: By definition, a wavefront must be moving faster than the local speed of sound in the medium to be called “shock.” Density, pressure, & temperature all get downright unreal. But... this might not even be that intense. It was just speculation (see MaJoC the Filk's post above.)

I took OP as more concerned about the overpressure of the sheer volume of gas being suddenly released into the enclosed space. Have to be a pretty darn big bag(s?) in a really sporty, little, air-tight, econo number to make that kind of difference methinks.

And, like I said, an itty bitty firecracker, no shock, no volume, will still do plenty permanent hearing damage.

All of the above grossly oversimplified beyond any utility for modern 'smart' multi-bag systems on two continents.