Can a Grenade Be Fatal Under Water?

The question of whether a grenade can be fatal under water is a critical one, especially for those involved in underwater activities such as diving or marine operations. The answer is emphatically yes, as demonstrated by the physical properties of water and the effects of explosions and compression forces.

The Physics of Grenade Detonation Under Water

Modern Thrown Fragmentary Grenades: Most modern grenades designed to explode on impact, or those that contain fragmentation shells, will go off in water. This is due to the density of water and how it affects the detonation process. Water can transmit the concussive force more strongly than air, leading to significant injuries or fatalities.

Concussion Grenades: Similar to the fragmentation version, concussion grenades are also likely to explode in water. These grenades are designed to cause shock waves and disorient targets, but the intense pressure and over-pressurization of the water can trigger their detonation.

40mm Grenades: The 40mm grenade is a notable exception. It may or may not detonate in water, depending on external factors such as whether it hits an object or if it has a self-destruct fuze. However, even if it doesn't detonate, the proximity to the explosion can still be hazardous.

The Dangers of Water-Transmitted Explosive Forces

Depth Charges and Submarines: The principle is similar to depth charges used to sink submarines. The explosion in water generates a concussive pressure that can rupture organs and cause severe damage. Just as a depth charge can sink a submarine, a grenade can prove deadly to anyone close enough to the blast.

Sound Waves: Sound transmitted through water can pose an additional risk. According to German physicist Jürgen Altmann, the threshold for lung rupture and embolism due to sound pressure can range from 2.6 to 11 times atmospheric pressure. This can occur even at a distance from the blast, highlighting the need for caution.

Water's Effect on Grenade Fragments and Predators

Fragment Dispersal: While the explosives and metal fragments of a grenade can be lethal, they typically do not travel far in water. Due to the density of water, these projectiles quickly lose velocity and fall harmlessly to the bottom. This effect is akin to how depth charges work, where the force dissipates before reaching the target.

Underwater Predators: In environments like Vietnam's harbors, patrol boats often used concussion grenades to deter and kill divers. The underwater concussion caused by the explosion created a deterrent that significantly reduced the threat of divers to the boats.

Primary Blast Injuries and Beyond

Water's Amplification of Forces: Water is a dense medium, which means that it transmits the shock waves from an explosion more effectively than air. This amplification can lead to more significant injuries and a shorter fatal range for the grenade's fragments.

Blast Fishing: The concept of blast fishing, where explosives are used to kill fish, underscores the potency of underwater explosions. These explosions can cause a range of injuries, including blast-induced lung injuries and rhabdomyolysis. Rhabdomyolysis, also known as shattered muscle, occurs when muscle tissue is destroyed and breaks down into components that can cause kidney failure.

Conclusion

Dealing with grenades in underwater environments requires a thorough understanding of their effects. While water may dilute the impact of metal fragments, the concussive force of an explosion can still be fatal. Divers and underwater personnel must exercise extreme caution to avoid such hazards.

Understanding the physics behind these interactions can save lives and ensure the safety of all those involved in underwater activities. Always prioritize safety and avoid using explosives in water unless absolutely necessary.

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