A Polk county hospital caring for 250 patients went dark as Hurricane Irma swept through the area.
Irma's hurricane-force winds knocked out power to Winter Haven Hospital around 1 a.m. Monday.
The generator system kicked in, but a problem three hours later forced a hospital-wide blackout.
"It was all-hands on deck to remedy as fast as we possibly could," Winter Haven Hospital president Steve Nierman said. "You can try to anticipate every viable situation of what might happen and there's probably something that will still go wrong. And that was the perfect storm."
Nierman told ABC Action News, when the primary fuel tank went dry, a glitch kept fuel in the reserve tanks from reaching the generator.
"When it went to pull fuel, diesel fuel, a vapor lock, or trapped gas in the pipe, prevented the diesel fuel from getting from the reserve tank into the actual generator," said Nierman.
The hospital performs monthly tests on its generator system, but not long enough to test reserve fuel tanks.
"That was the lesson learned, is when we do those monthly tests, it needs to probably be much more than four hours to make sure that those reserve tanks are fully functional as well," said Nierman.
Doctors and staff, a team of more than 600 people, worked by flashlights as the hospital went dark for about 3.5 hours.
"It wasn't total darkness when you think that everybody has their cell phone lights plus flashlights and other lighting devices in the hospital," said Nierman.
Officials say doctors did not perform surgeries during the blackout. One patient did go into cardiac arrest. Hospital staff resuscitated the patient who is now recovering.
"The staff member was able to successfully do that with lighting that was battery operated," said Nierman.
"It's a relief and also it's kind of amazing that the staff was able to work through it, you know, and still make sure everyone was safe and secure," said Aaron Wilson, whose mother is a patient at Winter Haven Hospital.
Nierman tells ABC Action News, the hospital has installed new pumping devices to make sure that fuel in reserve tanks will properly flow into the generator.