Miniature Lethal Munitions: The Technology Of The Pager Bombings

At 3:450 pm local time in Lebanon yesterday, the portable paging devices worn by some 3,000 member of terrorist group Hezbollah simultaneously exploded. At least nine people were killed, and hundreds more seriously wounded. This event would seem outlandishly implausible in a techno thriller, but reality is not always plausible.

Nobody has claimed responsibility for the attack, but it is hard to see that it could have been carried out by anyone except the Israeli intelligence services, who have a track record of audacious and technologically-sophisticated long-range assassinations, such as the remote-control killing of Iranian nuclear scientist Mohsen Fakhrizadeh and the killing of terrorist Yehiyeh Ayash aka "The Engineer" with a booby-trapped cellphone containing explosive.

How was the attack in Lebanon carried out?

Fire In The BATLab

Early speculation focused on the idea that this was essentially a software hack which caused the pager batteries to overheat and explode.

The batteries used in many mobile devices can be vulnerable to a condition known as thermal runaway. As the battery heats up during operation , it starts a chemical reaction within the battery cell which produces more heat. This in turn accelerates the reaction and within seconds a battery can reach 750 F / 400 C. At these temperatures the battery compounds break down, producing gases which expand and rupture the battery casing. The gases are typically organic solvents which are flammable and can be explosive.

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There have been several high-profile accidents from such events, like the series of fires associated with Galaxy phones in 2016, a spate of burn injuries from e-cigarettes and a laptop which caught fire on a Lufthansa flight last year,

Fires from batteries usually only occur where cells are damaged or there are manufacturing flaws. Most batteries are inherently safe in normal usage. Sandia National Laboratories Battery Abuse Testing Laboratory (BATLab) carries out extensive testing on batteries from button-sized to units powering electric trucks, and the chemistry of thermal runaway is well understood.

It might be possible to design a battery which would overload on command, but this would produce fires rather than the blasts seen in Lebanon. CCTV videos of the attacks indicate they involved something more explosive.

Miniature Munitions At War

The suggestion is that Hezbollah were hit by a supply chain attack, in which explosive devices were inserted into the pagers either at the point of manufacture or during transit from the maker to the users. The AR-924 pagers used weighed just 3.3 ounces / 95 grams including battery so this would require an extremely small bomb.

Some of the smallest anti-personnel explosive devices ever fielded were the U.S. BLU-43 ‘Dragontooth’ mines used in Vietnam. These asymmetric mines are about two inches across and resemble a maple seed. They were scattered from the air to make trails impassable. Each mine weighs less than ¾ ounce (20 grams) and is filled with 1/3 oz / (9 grams) of nitro-paraffin liquid explosive. It should be possible to incorporate a similar quantity of explosive into a pager bomb.

Dragontooth mines tended to injure rather than kill. The Russians have widely used their own version in Ukraine – the PFM-1, known as ‘Petal’ or ‘Green Parrot,’ a scaled-up model with 1.3 ounces (37 grams) of liquid explosive. These typically cause what a Human Rights Watch report on mines in Ukraine describe as “traumatic amputations of the foot or lower leg” rather than killing outright. The much smaller BLU-43 usually caused foot injury.

The U.S. deployed some even smaller air-dropped mines during the Vietnam conflict, delivered by the thousand in cluster bombs. Known as ‘Gravel mines’ or ‘Button bombs’ these were simply fabric pouches, some not much bigger than a postage stamp, filled with shock-sensitive explosive. The mines were stored in liquid which evaporated after they were dropped, activating the mines.

Gravel mines typically contained about 1/3 oz / (9 grams) of Lead azide/RDX explosive, and were not very effective, the USAF calling them “little more than a nuisance." One of their main functions was to act as a warning of the presence of a Viet Cong patrol when they set one off.

More recent U.S. research has developed extremely small and presumably effective micro-munitions for drone operations. This work is largely classified.

Pager Bombs

Blast alone is not an effective lethal mechanism. Anti-personnel weapons are generally packed with large amounts of shrapnel, as the flying metal causes far more serious injury than blast alone. The Vog-17 grenade, widely used as a drone bomb in Ukraine, weighs 12 ounces (350 grams) but only contains 1.2 ounces (35 grams) of explosive.

If the attackers were able to tailor the explosive device within the pager, it may have been positioned to use other pager components as shrapnel, making it more effective than the mines above. Given that the pager is designed to be worn on a belt clip with one side facing towards the wearer’s body, a directional explosive could be engineered; this would be far deadlier than the tiny size of the device would suggest. The hundreds of Hezbollah operatives reportedly seriously injured suggest the device was notably lethal for something so small.

This attack looks like a one-off, and surely terrorists and others will now be highly aware of the risk of explosive devices concealed in portable electronics. But it is an impressive demonstration of a highly-targeted attack using a few pounds of explosive to strike literally hundreds of opponents at once.