The incident occurred in June 2022 and the workers were contractors that did not work full-time for the factory. More than two dozen rescuers responded to the incident at the Mars Wrigley factory in Elizabethtown, Pennsylvania, and one worker was transported to hospital by helicopter, according to local media.
It was not clear how they fell into the tank, but a hole had to be cut into the bottom of the partly-full tank in order to pull them out.
The Occupational Safety and Health Administration (OSHA) report labelled the incident "serious". It says the workers were hired to clean tanks and were not provided with proper safety training.
According to OSHA, the workers were not authorised to operate in the tanks and were also not sufficiently trained with the safety procedures surrounding factory equipment.
“The employer did not ensure that the employee had the knowledge of the type and magnitude of the energy for the task,” said OSHA, adding: “The host employer did not provide the outside employer with the correct energy control procedure or work authorization permit.”
It noted that the workers fell into a batching tank - a tank used to mix ingredients - for Dove chocolate, a brand sold in the US. In the UK and elsewhere, Dove is sold as Galaxy.
A spokesperson for Mars Wrigley said: "The safety of our associates and outside contractors is a top priority for our business.
"As always, we appreciate [the Occupational Safety and Health Administration's] collaborative approach to working with us to conduct the after-action review."
In addition to Dove/Galaxy, the company produces several popular sweets such as M&Ms, Snickers and Twix.