The Johns Hopkins All Children’s Outpatient Care in Tampa, Florida, was evacuated due to a rupture in a bank of lithium-ion batteries used to provide backup power for an MRI machine. On the morning of July 20, hospital employees smelled a strange odor coming from an MRI room and called in the emergency, according to a report by ABC Action News Tampa.

Emergency personnel arrived and evacuated 80 people, three of whom were later treated at a hospital. They determined the smell was caused by a bank of 30 lithium ion batteries designed to provide backup power for the MRI machine in a power outage. In the hours leading up to the incident the hospital had experienced power issues.

At first rescue crews did not believe there to be an imminent threat of an explosion because the odor didn’t smell electrical, however it was determined that the smell was hydrogen gas leaking from two ruptured batteries. Each battery in the bank is large, weighing 100 pounds each so firefighters evacuated a larger area and called in the local sheriff’s bomb squad.

Hydrogen gas is extremely flammable and lithium ion batteries, once ignited, burn hot and are difficult to extinguish. By the late afternoon, the batteries were able to be removed without incident and they were soaked in sodium bicarbonate (baking soda) to neutralize them for disposal.