A study on unexploded bombs from World War II has revealed that a certain explosive compound contained within them is becoming increasingly sensitive to impact, meaning it could detonate if dropped during handling. This explosive compound, known as amatol, was widely used during World War I and World War II. The findings were recently published in the journal Royal Society Open Science.
Unexploded aging munitions are becoming increasingly hazardous. Image Source: Geir P. Novik
"If it hits the ground, it's definitely going to explode, unlike TNT (trinitrotoluene)," said Geir Petter Novik of the Norwegian Defence Research Establishment. "Based on our findings, it can be said that handling it is relatively safe, but you can't handle it like TNT."
There are millions of tons of unexploded ordnance scattered around the world, some in old munitions depots and some in bombs and shells that failed to detonate upon launch or impact. Novik says a common misconception is that the danger of these unexploded ordnance decreases over time.
In a study conducted in 2022, Novik tested samples extracted from World War II bombs and shells containing two of the most widely used high explosives, TNT and PETN (pentaerythritol tetranitrate), and found that their explosive properties did not degrade over time.
Now, Novik has extracted five Amatol samples from unexploded World War II bombs and shells found in Norway and tested their impact sensitivity. The tests involved dropping weights from various heights onto small samples to see what it would take to make them explode. All five samples showed higher sensitivity to impact than expected, with one sample being four times more sensitive.
Novik says these findings will change the way he and his team handle unexploded ordnance. For example, when clearing rubble, they will transport smaller quantities at a time. He plans to try to identify the reasons for the increased impact sensitivity, "We suspect it's the formation of sensitive crystals or salts."
This could be due to contaminants in the manufacturing process of the munitions, reactions between internal aging and the metal casing, or simply aging.
Amatol is an explosive made by mixing TNT and ammonium nitrate. Novik says it's difficult to say how much unexploded ordnance in the world contains Amatol, but of the 20 bombs and shells he cut open for this study, five contained this substance. There have been numerous incidents of unexploded ordnance detonating. For example, in 2023, a World War II bomb exploded during disposal in Portsmouth, England.
Related Paper Information: https://doi.org/10.1098/rsos.231344
