A toddler survived falling off a 15th-floor balcony. Experts explain how.

A child fell from a 15th-floor balcony of this apartment building in Montgomery County, Maryland, and landed on a bush and survived. Photo / Dan Morse, the Washington Post

Incredible. Amazing. Miraculous.

There have been many ways to describe a 2-year-old boy surviving a 15-storey free-fall off an outdoor balcony into a small bush last week in Montgomery County, Maryland.

But any discussion quickly gives way to the question: How?

“The first thing to realise is that it’s not the fall, it’s the landing,” said Anette Hosoi, a physicist and mechanical engineering professor at the Massachusetts Institute of Technology.

Hosoi teaches fluid mechanics, which she said covers the mathematics needed to study how humans fall. For more than 10 years, she has made the “physics of falling” a subspecialty.

In broad terms, she said, the boy’s light weight and landing spot helped. “That bush absorbed a lot of energy for this child,” she said. “Lots of things went his way.”

Just after 2pm last Thursday local time, police and paramedics were called about the fall at the Enclave Apartments, a group of three high-rise buildings in the White Oak section of Montgomery County.

They treated the boy and took him to a nearby hospital with injuries including a broken leg and multiple internal injuries, police said. They described the injuries as “non-life-threatening” and said the child is expected to survive.

No criminal charges have been filed, and detectives continue to investigate what led to the fall. The boy’s parents could not be reached for comment.

Hosoi said the basic formula that force equals mass multiplied by acceleration conveys an advantage to toddlers. That must be weighed against a falling person’s force against the atmosphere - larger for adults and calculated by multiplying a “drag constant” by their velocity squared.

And a big factor is terminal velocity, or the maximum speed a person reaches when falling a long way.

Hosoi said 15 floors was not enough for the child to reach his terminal velocity, and he was falling at a rough estimate of 65 km/h when he reached the bush, compared to what would have been approximately 95 km/h for an adult.

And all those factors, Hosoi said, don’t account for how much of the child’s kinetic energy was absorbed by the bush.

Another way to look at it, Hosoi said, is to take a step back and think about animals that are smaller than humans.

“It turns out there is a critical size here - and it’s a rabbit,” she said.

Hosoi estimates that if a rabbit falls out of an aeroplane and lands on dirt or something softer, the rabbit has a 50% chance of not being injured. From there, she said, you can look at animals and humans that are smaller or larger than rabbits.

“The rabbit is the borderline case,” Hosoi said. “Mouse survives. Smaller rabbit survives. Bigger than a rabbit probably results in injury.”

Joshua Abzug, a paediatric orthopaedist at the University of Maryland Medical Centre, said the child was fortunate to have landed where he did.

The bushes were relatively small - 90cm or less - but had strong branches inside them as long as 2.5cm in diameter. And the size of the bushes, Abzug said, probably didn’t matter as much as their composition.

The branches probably absorbed energy for the falling child and slowed him down. One way to look at it, Abzug said, is damage to the branches replaced more damage that could have occurred to the boy’s bones and internal organs.

Abzug said that a “softer” bush may not have slowed him down enough before hitting the ground.

“As those branches twisted and broke, that’s where the force went. They absorbed energy and slowed the child down,” Abzug said. “The child landing in that bush probably saved his life.”

The child fell in bushes and suffered non-life-threatening injuries, police said. Photo / Dan Morse, the Washington Post

Abzug also cited the child’s light weight - and the laws of physics - saying that he was not falling as fast as an adult would have been falling.

One thing that is fairly consistent during falls, he said, is that humans try to right themselves as they are falling so that they land facing down with their arms out.

Abzug said that as the child was falling, he probably did the instinctual thing by righting himself and breaking the fall with his hands - as if he thought maybe he had just fallen while walking across the floor.

Abzug, who also serves as the deputy surgeon-in-chief of University of Maryland Children’s Hospital, sees as many as 150 children a week between the hospital and his outpatient practice.

Many have been injured from falls - out of cribs, at playgrounds, from trees and, less commonly, from windows or off roofs. Rarer still, he said, are children falling from apartment balconies.

He stressed that parents must always keep in mind how curious and mobile children are - and take steps to keep them from falling from any height. That includes having window locks, sliding door locks and, depending on their ages, keeping children off trees, monkey bars and other things off the ground.

Katie Donnelly, a paediatric emergency medicine physician at Children’s National Hospital in Washington, said parents sometimes overlook how a child’s natural curiosity can bring long falls into play.

“Balcony falls and window falls are a major concern that caregivers don’t necessarily recognise the danger of,” said Donnelly, who’s also the medical director of Safe Kids DC, a group devoted to keeping children safe and reducing risks for them in their homes, in cars and elsewhere.

Parents should not rely on screen doors or screen windows. “They’re meant to keep bugs out, not keep kids in,” she said.

And they should keep windows and sliding doors locked, she said. Parents should not allow kids on decks or balconies without an adult. Some parents may see a 1m solid railing and assume safety, not realising there is a chair or other object nearby that can be moved to the ledge.

“Kids will push it, climb it, jump on it - being kids. And from there, they can easily fall,” Donnelly said.

As they age, they can simply climb up the railing, she added. “Kids are smart and can climb on things and over things,” she said. “They are fast and determined.”

Donnelly said parents should assume that no fall over several metres is safe and that any fall over one floor can be deadly.

“It really depends on what kids land on and how they land,” she said.

Abzug said that the belief held in some quarters that children’s bones somehow make them less likely to break than adult bones isn’t necessarily true.

While kids may have a certain “plasticity” to their bones, their bones also are more porous and susceptible to compression and buckle fractures, he said.

The doctor also invoked a higher force as playing a role in the toddler surviving.

“I think that it was by the grace of God that this child lived,” Abzug said.

It was a view shared by Katie Griffin, who works on the first floor of the apartment building as a caretaker. “It had to be Jesus,” she said.