The CDC edited the toxicology profile for vinyl chloride, massively increasing the lethal exposure level and removing information about how the chemical affects children, just two weeks before the train derailment in East Palestine, Ohio that spewed vast quantities of the chemical into the environment.

The CDC update changed the lethal exposure from 100PPM to 100,000PPM. The lethal exposure level had remained the same for 17 years before the CDC decided to update the number just prior to the derailment, where highly toxic chemicals spilled or were burned off, leaving a chemical stench in the air nearly two weeks later.

Read more:
https://ussanews.com/2023/02/17/inside-job-cdc-changed-toxicity-info-on-vinyl-chloride-days-before-derailment/