This is what happens when you're struck by lightning

The odds are one in a million that you will be struck by lightning this year.

Still, on average, about 300 people in the U.S. are injured and 30 are killed each year, according to the National Weather Service.

On Tuesday, a lightning strike injured three workers at Park Tudor High School. One of the men went into cardiac arrest and was revived after 12 minutes with the help of a school officer, William Hagy, who performed CPR. All three are doing well now, according to a spokesman from St. Vincent Indianapolis Hospital.

What is sustaining a lightning strike like? And what happens to those who survive?

Senate slugfest:9 fights so far in Indiana's bare-knuckle U.S. Senate race

'A big teddy bear':Southport community remembers slain officer Aaron Allan

Lightning is one of the top three storm-related killers in the United States, according to the National Weather Service, but it is also one of the least understood weather phenomena. 

Each event, however, certainly starts with a growing thunderstorm cloud, a negative charge building in the bottom of the cloud and a positive charge in the ground below. When the difference between charges grows too great, the insulating capacity of the air breaks down and electricity is discharged.

Bolts of electricity — each can carry up to 200 million volts — typically pass over a victim rather than directly through. The flashover can singe clothing, vaporize sweat and superheat metal buttons and belt buckles. 

Not all strikes are direct hits, but most do leave outward marks, whether burns or strange spidery bruises, known as Lichtenberg figures, which trace the path of electricity that forced blood cells out of capillaries.

"A lot of folks bounce back with no injury," said Charles Miramonti, the chief of Indianapolis' emergency medical services and Eskenazi's chief of care integration.

For those with injuries, cardiac and respiratory arrest are the immediate concern, Miramonti said — all that electricity can fry signals and stop the heart. There can be internal and external burns, kidney failure and nerve damage.

"It's really what you don't see that can be concerning," Miramonti said. Only an entry and exit wound may be visible until surgery reveals further damage inside. 

Miramonti has seen only one lightning victim, while Miramonti was in residency two decades ago. He also has treated a few victims of electrical accidents, which are less mysterious but involve many similar symptoms.

Andy Isch, who was the trauma surgeon on duty Tuesday when the workers were taken to the St. Vincent trauma center in Indianapolis, said this was the first lightning strike he remembered treating, but with access to good diagnostics, therapy and rehab, people who survive lightning strikes should be OK.

Eleven people in the U.S. have died after being struck so far this year, according to the National Oceanic and Atmospheric Administration, while doing activities as varied as riding a horse, boating or walking up to their front door. In 2016, 39 people died. Top causes of death are cardiac and respiratory arrest.

Of this year's fatalities, two men in Florida died while working in construction.

Miramonti said emergency care for lightning strike and electrical injuries hasn't changed much, and research into long-term effects is limited. Some stories of survivors, collected by the National Weather Service, describe chronic pain, muscle aches, confusion, dizziness, hearing loss, personality changes and memory loss.

All in all, Miramonti said, only time will tell whether the man who sustained a cardiac arrest after Tuesday's lightning strike will face lasting effects or leave the hospital unscathed.

"The working crews yesterday got super lucky," he said.

Contact Ruth Serven at ruth.serven@indystar.com or 317-444-7753. Follow her @ruthserven.