WEST READING, Pa. (WHTM) – The National Transportation Safety Board has released a preliminary report concerning the deadly chocolate factory explosion that occurred in West Reading, Pennsylvania.

The board’s preliminary reports indicate that natural gas fueled the March 24 explosion and fire at the R.M. Palmer Co. factory — something investigators suspected from the beginning.

The report added, however, that there was no reported spike in gas usage or any work being done on the gas mains prior to the explosion. The “source” of the explosion is still under investigation, the NTSB said.

Interviews conducted with employees after the accident revealed that workers in two of the factory’s buildings noticed unpleasant odors on the afternoon of the incident, just before the blast. Those working in one building — identified by the NTSB as Building 2 — were sanitizing equipment when they detected an odor of natural gas. Those in Building 1 reported detecting a similar sulfuric smell.

“The employees in Building 1 recalled the smell of rotten eggs around the same time,” the NTSB wrote.

At least one worker told the Associated Press she notified management of the odor a half-hour before the explosion. When the blast occurred, that same woman caught fire and fell through the floor into a vat of liquid chocolate.

The NTSB’s report that there were “about 35 office staff and 70 production employees” working in the factor’s two buildings at the time.

Seven people died in the explosion, and eleven others were injured.

R.M. Palmer Co. said in a statement that it was aware of the NTSB report but said that the company had been “asked to assist” in the federal investigation and was therefore precluded from commenting on the investigation and allegations “surrounding the incident.”that may be made in litigation relating to the incident.”

“Our employees’ safety and health has always been, and will continue to be, of paramount importance and we extend our heartfelt condolences to those who were impacted by this tragedy,” the company continued in the statement.

The NTSB’s full report is available on the agency’s website.

The Associated Press contributed to this report.