It's powerful to have investigative powers not be hard-tied to regulatory powers (see NTSB / FAA... in fact, I believe that was the actual model chosen for USCSB).

I'm totally not in the field, so I have no idea how often OSHA/EPA follow up on USCSB recommendations, and if OSHA and EPA's remit are sufficient to be able to enforce/mandate the majority of USCSB recommendations.

For example in the video USCSB identifies that TPC had internally recommended and green-lit procedures for flushing out of use lines to prevent popcorn polymer formation, but did not actually implement the action.

I know in medical device land, this type of thing (say someone internally recognizes a risk to device safety in the manufacturing process, a mitigation is accepted and greenlit, but never actually implemented) would be subject to both quality audits (so by someone checking up on your ISO status), and potentially as part of FDA follow up audits. I don't know what the situation in this field would be like.