Explosions can be heard, but they are obviously quieter than normal explosions. But is this possible to accomplish with thermite? Well, as pointed out in the Active Thermitic Material paper, in April 2001 the American Chemical Society held a symposium on the defense applications of nanomaterials in which they stated:
At this point in time, all of the military services and some DOE and academic laboratories have active R&D programs aimed at exploiting the unique properties of nanomaterials that have potential to be used in energetic formulations for advanced explosives…. nanoenergetics hold promise as useful ingredients for the thermobaric (TBX) and TBX-like weapons, particularly due to their high degree of tailorability with regards to energy release and impulse management.The authors then go on to point out that:
The feature of ‘impulse management’ may be significant. It is possible that formulations may be chosen to have just sufficient percussive effect to achieve the desired fragmentation while minimizing the noise level.This certainly doesn't sound like magic or mythology to me. All it sounds like is science.
So yes, thermite can be formulated as an explosive, but it can also be formulated to reduce the explosive sounds. Certainly those close to WTC7 might have heard these explosions, and it is those types of witnesses Gage references.
Gage has good reason to criticize Mohr for claiming that WTC7 and other demolitions "sound completely different,” because as the NFPA 921 guide points out:
Although an explosion is almost always accompanied by the production of a loud noise, the noise itself is not an essential element in the definition of an explosion. The generation and violent escape of gases are the primary criteria of an explosion.Below is an edited version of Gage and Mohr's debate where I have added comments and videos to address the sound issue and other points raised by Mohr.
Unedited version of Gage and Mohr's debate with visual aides and download link.
9/11 Controversy Strikes Again at UC Boulder Face-Off
2/25/11 Answers from NIST to Questions by Chris Mohr, Journalist