SPOILER WARNING!!!

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From the Book

As he entered the room, he stepped over a flaming wastebasket and glimpsed a sleek black shape amidst the flames. He looked up and saw an old laptop lying on the desk, its internals ripped out.

“My head,” groaned Drake, falling to his knees and holding a hand to his temple.

“Shut up,” said the man. “Open that,” he said, pointing his rifle at the wooden cupboard in the corner. He shifted the rifle until it was pointing at Drake’s head. “Quickly.”

“Okay,” said Drake, shuffling forward and sliding the cupboard door open. He hunched over clutching his head and looked back at the bin. Black smoke was billowing out of the top and an acrid smell was filling the air. “My head,” he groaned, falling to his knees inside the cupboard, his hand dragging the door half shut as he fell. He squinted at the bin, which was glowing red.

“You’re dead,” snarled the man, lowering the rifle.

BOOOOOOOOM!

The Problem

Will has hidden during the terrorist attack on his uncle’s house, which leaves the house in flames. But Drake and the others aren’t so lucky, and are captured. At gunpoint, Drake is forced to search for Will. As he enters the study, he sees a burning laptop battery in the waste-paper bin. Realizing the danger, Drake takes cover just as the battery explodes, temporarily taking down his captor and giving him enough time to counter attack.

The Calculation

Will has placed the battery intentionally in the fire to distract the terrorists. But are exploding laptop batteries possible? What sort of damage might one do? That’s what we’ll calculate here.

Energy in a Laptop Battery

Modern laptop batteries are typically Lithium Ion batteries, which have a thermal energy capacity of approximately 0.5 Megajoules (MJ) per kilogram of battery. If we assume that the laptop battery Will has used is about 1 kilogram, we can calculate the battery’s specific energy:

Battery energy = mass of battery * specific energy

Battery energy = 1 kg * 0.5 MJ / kg

Battery energy = 0.5 MJ or 500 kJ

To get a feel for what 500 kJ of thermal energy is like, we can examine the energy of a hand grenade.

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An M67 hand grenade has approximately 0.18 kg of Composition B explosive inside it. According to this textbook, the energy density of Composition B is 17.4 MJ / kg.

Grenade energy = Composition B weight * energy density of Composition B

Grenade energy = 0.18 * 17.4

Grenade energy = 0.18 * 17.4

Grenade energy = 3.1 MJ

So using this very approximate calculation, the grenade has about 6 times the energy of the laptop battery. The grenade explosive also releases its energy much more quickly than an exploding laptop battery, and has dangerous metal shrapnel.

However, this approximate calculation shows us that it sounds reasonable that if a laptop battery were to explode, it would probably do a reasonable amount of damage, as it does in the book.

 Have a look at this exploding lithium ion battery pack fire: