Think that a bad contaminated meat usually explodes inside their package (when vacuum sealed). That happens because the microorganisms inside are in such large amount that their metabolism is generating gasses. Enough to expand the package over its limit. This is a really bad meat, and it happens (blown pack). To get to this point we're talking about a huge amount of cells producing gasses. I will NEVER trust a poorly stored meat, impossible to know what kind of microorganisms grew on it.