HAGERSTOWN, Md. (DC News Now) — Things were back to normal on Monday at the Amazon warehouse on Wesel Boulevard after a carbon monoxide alarm was activated over the weekend.

Around 100 warehouse workers were evacuated from the warehouse as firefighters looked for the source of the scare. It was quickly determined that nickel-cadmium batteries on a forklift were venting hydrogen sulfide.

Hagerstown Fire Chief Steve Lohr said warehouse supervisors evacuated the building out of an “abundance of caution” amidst concerns carbon monoxide may have leaked.

“Once we were certain that we had isolated the incident we removed a particular lift truck from the warehouse to the outside,” Lohr said. “We ventilated the structure, which took some time – 30 million square feet of space.”

Hagerstown firefighters used air monitoring sensors before issuing the “all clear.”