"There is only the shot to the head to neutralize an individual wearing an explosive vest!" Really?
Although this view of the problem is commonly accepted and considered the most appropriate, if not the only option conceivable in such a situation, it would be interesting to put things in perspective to approach this problem with a much more objective view.
How far away?
First of all, how many operators have an idea, even vague, of the minimum safety distance to respect depending on what the threat carries:
An explosive belt?
An explosive vest?
an IED contained in a backpack or a suitcase?
A defensive grenade?
Looking at different existing safety templates, it will be noted that the commonly accepted distance to face an individual equipped with an explosive vest is 35m. Some experts will bring the nuance that this distance can, in extreme cases, be reduced by half if one is wearing heavy ballistic protections (full heavy vest class IV and KFS helmet equipped with ballistic visor) but in this case, we will speak more of "survivability" in case of explosion than real safety.
It must therefore be borne in mind, on the one hand, that first responders will not necessarily carry this equipment, and on the other hand that the recommended evacuation distance for third parties is at least 450m.
It should be noted that there are "charts" of safety distances and ways to assess distances using simple visual cues and elements of the immediate environment (especially in urban areas).
Operators will therefore have to locate and identify the threat and then deal with it effectively at a distance greater than or equal to 35m...
Why a shot in the head?
First of all, it is important to remember that many homemade explosives are unstable and relatively sensitive to shocks. This is particularly the case of the TATP which composed the vests of the perpetrators of the attacks of November 13, 2015. It is therefore excluded to take as a point to target the chest area (which would be the technique recommended in other situations), an impact in this area can initiate the load.
Then let's talk about terminal efficiency. To be 100% certain that nerve impulses (whether voluntary or purely reflex) can never leave the brain to reach the hand that activates the firing system, it is necessary to reach the cerebellum (seat of motor control) or the brainstem (medulla oblongata), which regulates vital functions such as cardiac activity, Breathing and is also a center of passage of motor pathways.
Concretely, if we are looking for a total and instantaneous neutralization, the area we must reach is barely bigger than a mandarin.
With a long weapon, firing a 5.56 of 62 grains (4gr) that generates 1767 joules or a 7.62x51 that generates almost 3800d, the hydrostatic shock (or dynamic pressure wave) caused during the impact should have the overall effect regardless of the area of the skull affected.
On the other hand, the effect is less guaranteed with a handgun that projects a bullet of 124 grains at about 350 m / s generating at impact an energy of 490 days. In this case, the accuracy of the shot will have to be at the rendezvous.
The point to aim will depend on the angle of fire: the base of the nose, the base of the ear or the middle of the neck.
But as part of our thinking, let's admit, for simplicity, that a shot anywhere in the skull will be reasonably effective, even with a 9mm projectile coming out of the 87mm barrel of a Glock 26.
How many operators are able to make such an accurate shot at 35m, even calmly, in ideal conditions, without time pressure?
Let's complicate things a bit... Stress...
Add to this equation the stress factor, because managing a terrorist wearing an explosive vest is undeniably not the least anxiety-provoking situation there is.
Intense stress generates on any human being a serious alteration of fine motor skills and significantly degrades his faculties whether motor or cognitive.
Finally, how many will be able to simply make the decision to pull the trigger? While knowing that there will not be absolute certainty that the individual in question is indeed carrying this type of explosive device, or simply that he intends to implement it! How many will drive from their minds the parasitic idea: "I'm going to get in trouble and maybe even go to jail if I shoot"? How many will not be able to simply accept the idea of taking a life, even if it is to save others and the opening of fire is perfectly justified from a legal point of view?
Let's complicate things further.... The movement...
Let us now add a new element hitherto often avoided: THE MOVEMENT!
In all likelihood, the adversary will not remain static, especially if he is challenged by the police. That a terrorist can behave like the "paper enemies" encountered in shooting ranges is therefore highly illusory: the operator will not be in conditions allowing him to take "quietly" a 35m compliant aim before pulling the trigger.
It is also possible that the adversary will rush in the direction of law enforcement or innocent third parties, to blow himself up on contact, thus maximizing the effect of the charge he carries.
And stopping an individual in full race even by touching lethal areas is undeniably not an easy task (cf: Coulibaly coming out of the Hypercascher running under a deluge of lead and in this real case there were more than ten RAID operators trying to stop him by a heavy fire).
To stay on the theme of the movement, the opponent must not be the only one to be mobile. Unless the stress level of the operator inhibits it by generating for example a state of astonishment, it will either be fleeing or fighting. In the latter case, he should do it by moving.
"What do you call someone static in combat? We call it a victim!"
What if the threat was not limited to the explosive vest?
Let us add one more element to this situation: our adversary can also be armed and open fire in our direction and/or on third parties. For the record, in addition to their TATP vests, the Bataclan terrorists were armed with assault rifles (Kalashnikov).
It is not only a question of neutralizing an individual who risks detonating his charge at any time but also of fighting an armed opponent by protecting himself as best as possible from his shots.
In the chaos of a panicked crowd...
Since terrorist attacks are aimed at causing maximum casualties, the threat to be neutralized will probably be in the midst of many innocent people. Panic is therefore to be expected: panicked passers-by fleeing danger will probably pass through the fire areas, and, in the background, may be panicked or prostrate people.
In this chaos, you are expected to have the right gesture. It must be borne in mind that members of the security forces are fully responsible for each shot they fire. Therefore it is not acceptable to cause any collateral damage.
To put it simply, if you pull the trigger, you will absolutely not have the right to miss your target.
Let's resume by summarizing the situation:
In this case, you must perform a headshot with standard sighting devices, on an individual who moves, and who shoots (on you and / or on third parties), being yourself in motion, under intense stress. What's more, you have no right to make mistakes: you must not cause collateral damage in a chaos of panicked crowds, and this shot, you must probably perform it with a handgun, under pressure of time at a distance of more than 35m.
To this, it can also be added that most first responders will not be equipped with aiming aids on their handguns or illumination systems and that the ambient conditions may not allow them to make shots with the expected accuracy.