The US government did all sorts of crazy tests on people in the 50s: https://en.wikipedia.org/wiki/Project_MKUltra
https://en.wikipedia.org/wiki/Unethical_human_experimentatio...
This is why a lot of people (myself included) take a hard-line position of any kind of testing involving humans. Yes, it's often a waste of time to run many trivial experiments by an IRB first, but history has shown that some people seem unable to make this kind of judgement call probably. Really, in many case, an IRB simply serves the same purpose as assert(3); it's a "sanity-check". Like all sanity check, in theory it shouldn't be necessary, but history shoes it's worth checking anyway.
IRBs are effective at checking back everyday scientists. I somehow doubt an IRB panel would be need to be consulted by someone powerful enough to have the authority to load a crapton of bacteria onto a boat and spray it into SF.
Also, one of the steps in a typical IRB process is to sanity catch mistakes. As mentioned in another post, the people spraying bacteria over SF probably believe they were doing a "safe" experiment about dispersion properties. In an environment were it was regularly expected use an approval process, there might have been a chance for someone with biological knowledge to inform the experimenters of their error.