I - INTRODUCTION

A brief presentation of ballistic protections exists on this site.  The subject of bullet-proof vests is covered. It seemed to us that the subject of individual protection deserved some deepening. As the person in charge of the lesion ballistics unit at the Centre Technique de la Sécurité Intérieure, we participated in the think tanks that contributed to the generalized implementation of individual ballistic protection within the police force.

This presentation is based on a series of conferences we have given to bulletproof vest users and trainers. It has been adapted so that it can also be useful to anyone who will have to work in a hostile environment.

These pages are mainly addressed to the non-specialist who is interested in this field by curiosity, or by necessity.

As for the specialist, he may find in this document some common threads allowing him to convey a message to future users.

II - THE ROLE OF THE BULLETPROOF VEST

• Introduction

The bulletproof vest is a means of protection. Its acquisition and its wearing are authorized, at least in France, country where these lines are written.

Some authors, respectable and competent, consider the bulletproof vest as a weapon, but a defensive weapon. They therefore make a distinction between weapons intended for attack and weapons for defense. This distinction seems, in general, difficult to maintain. Indeed, an attacker may very well equip himself with a bulletproof vest in order to increase his aggressive potential, since he will be more difficult to neutralize than if he were not wearing one. The consequences of such a categorization could lead to the possibility that body armor would suffer the same fate as other defensive weapons, i.e., that it would be classified by the legislator, that its purchase and wearing would therefore be subject to authorization and that only certain people would be authorized to be protected.

While acquisition is therefore easy, the choice of protection adapted to the threat is more delicate. To solve this problem, it is necessary to take into account a number of elements, including why and how to use a bulletproof vest, understand how this ballistic protection works, what are its constituent elements, know its protective capabilities and, above all, its limits.

We will review a number of points that will gradually shed light on the subject.

II -1 - THE NEED FOR A BULLETPROOF VEST

• First point. Why a bulletproof vest ?

The question seems superfluous. However, it has the merit of clarifying the risk inherent in a projectile strike.

The role of a bullet-proof vest is to stop projectiles that are likely to penetrate more or less deeply into the body, even through it, and thus cause injuries.

• A bulletproof vest, yes, but to protect against what ?

Until then, the term projectile had remained rather general and even vague. It is now necessary to specify the threat. It turns out that it can be reduced to two types: projectiles fired by firearms and shrapnel in wartime.

In peacetime, firearm projectiles are the major threat.

In wartime, in the field, although firearm projectiles are obviously not to be neglected, the risk of injury is mainly due to shrapnel from explosive devices: grenades, shells, directed action anti-personnel mines, secondary shrapnel torn from a target on impact, etc... During combat, the atmosphere is heavily charged with metallic particles of all shapes, masses and speeds.

II-2 - RISKS IN CASE OF A PROJECTILE STRIKE

• Feedback from the field. The risk of bleeding

Excluding brain damage (head injury), which is usually fatal, although specialists report exceptions, the death of an individual hit by a projectile who does not receive immediate care is considered to be due to hemorrhage. If he or she does not die directly from hemorrhaging, the drop in blood pressure can lead to physiological disorders (shock) that can be irreversible and, ultimately, fatal.

Autopsy findings show that, in the case of thoracic or abdominal injuries, the risk of death correlates well with the depth of the injury. This is easily explained, on the one hand by the fact that the longer a projectile travels in an organism, the more tissue it damages and the greater the hemorrhagic phenomenon and, on the other hand, that the large vessels are located deep inside the body and can therefore be affected. In addition to hemorrhaging due to damage to the vascular system, certain highly vascularized organs, such as the liver, can cause significant blood loss.

The heterogeneity of the human body means that not all anatomical regions present the same hemorrhagic risks in the event of projectile penetration. This observation makes it possible to give priority to certain areas over others in order to meet the ergonomic constraints that will be discussed below.

II-3 - THE HUMAN BODY AS A SYSTEM TO PROTECT

• Study of the human body as a system to be protected

Thorax and abdomen

An observation of the body, according to different planes, tends to show that the blood density is not homogeneous. The large vessels likely to cause massive hemorrhages in the event of an injury are rather located in the center of the thorax and the abdomen. This anatomical region should therefore be given priority by offering maximum coverage in width as far as possible. In height, taking into account mobility constraints, the region to be covered is delimited, at the top, by the large vessels located above the heart behind the manubrium (the suprasternal notch can be used as a high anatomical reference point). At the bottom, the limit is, still taking into account the mobility constraints, the bifurcations of the abdominal aorta and vena cava. 

Vascular network. Front view	Vascular network with the liver. Front view

Vascular network with the liver. Side view	Vascular network with the liver. Back view

It should be noted that some bulletproof vests, qualified as heavy or intervention, sacrificing mobility, offer a protection going down : genital triangle, femoral triangle (see the image below).

Bulletproof vest with pelvic and shoulder protection

The limbs

They are generally not among the areas to be protected as a priority. Especially since they can be easily tourniqueted if we exclude Scarpa's triangle (femoral triangle) which, for this reason, is sometimes taken into account by certain ballistic protections (see the image above).

Some manufacturers take into account the protection of part of the lower limbs, necessarily to the detriment of ergonomics (see image below).

Bulletproof vest with thigh, pelvic and shoulder protections

• Summary

A few key points about the role of a bulletproof vest are worth remembering for the designer of personal ballistic protection or its wearer :

• The human body is a heterogeneous, complex and fragile system when hit by a projectile ;


• The role of a bullet-proof vest is to cover the body zones in front of which the organs and systems that must be protected are located ;


• The majority of the organs essential to life are located in the thorax and abdomen, cavities belonging to the trunk ;


• Deeper, in its cavities, are the large arterial and venous trunks which constitute, with the heart and the highly vascularized organs, extremely vulnerable regions ;


• The vulnerability of these organs is just as important when shot in the back ;


• In addition, in the back, the spinal cord contained in the spine is particularly exposed. The spine does not provide any ballistic protection for the spinal cord or for the large vessels and other organs.

• Conclusion

Any penetration of a projectile in the thoracic or abdominal region, regardless of the direction of the shot, is potentially fatal.

II-4 - A BALLISTIC PROTECTION, YES BUT...

• Not everyone is equal when it comes to gunshot wounds

Feedback from the field shows that the chances of survival after being hit by a projectile are highly dependent on the environment (urban or rural environment, theater of military operations, etc.). The speed of the intervention on the injured person is a decisive factor (firemen, paramedics, frontline medicine for the armies). Nowadays, in our highly civilized societies, any decrease in the number of firearm fatalities tends to be interpreted as a reduction in aggression, and therefore an increase in safety. In reality, it is rather due to the rapidity and improvement of the care of the wounded by the rescue and medical services, to which we must pay tribute.

• Bullet-proof / shrapnel-proof protection: nuance... and mistrust

To potential users : a shrapnel-proof protection (helmet, vest) is not a bulletproof protection. Many times we have had to demonstrate this to users, especially of flak helmets, who, believing themselves to be protected against a 9 mm parabellum projectile, but nevertheless suspicious, came to consult us. By slightly dismantling the cap, we showed them the small label, admittedly not very easy to access, stuck on the inside of the shell specifying the ballistic level: STANAG 2920 shrapnel 1.106 g, 600 m/s. Nothing to do with a 9 mm Parabellum projectile, which can have very different speeds depending on the length of the barrel of the weapon that fired it.

Often the user cannot choose his ballistic protection. It is imposed on him and usually provided by personnel who, although they have no particular knowledge, may exaggerate the quality of the product. A good reflex is to read the labels, as we will see below.

• The particularity of bladed weapons

Bladed weapons are subject to their own studies and tests. To protect oneself from them, it is necessary to use specific protections or "anti stab" vest. The protection against this kind of aggression is not at all assured by the soft bullet-proof vests intended to protect handgun ammunition (.38 Special, 9 mm Parabellum, 357 Magnum). The same is true of bow and arrow shots, which have penetration powers that are sometimes far superior to those of firearm projectiles. The explanation will be exposed later and for the moment it is sufficient to know that the fibers that make up flexible ballistic packs do not have good resistance to shearing, a mode in which they are used with knives and other sharp elements. But let's be reassured : you are better protected against stabbing by wearing a bulletproof vest than without.

To be noted

Faced with the weakness of soft body armor against knives, some manufacturers offer body armor to which an anti-stab element has been added and specify the level of resistance which is defined, according to standards, by the impact of a standardized blade. The force of the impact, given in joules, varies according to the desired level of protection.

III - HOW A BULLETPROOF VEST WORKS

A well-designed ballistic protection must fulfill two missions: stop the projectile and limit the rear trauma.

III-1 - STOP THE PROJECTILE

Protecting an individual from projectiles is not difficult in itself. But when it comes to doing so with individual, portable protection that is as light as possible, the equation is more complex. The challenge is to find materials with high mechanical strength that are as light as possible. Fortunately, technology is providing solutions.

III-1-1 - MATERIALS USED

A long time ago bulletproof vests were made of metal plates forming a tiling. Their heavy weight and relative rigidity limited their use.

Nowadays, fabrics made of fibers with high tensile strength are used. They are said to have a high tensile modulus.

The main fibers used are para aramid fibers (Kevlar®, Twaron®,...) and polyethylene fibers (Spectra®, Dyneema®,...). The choice between the two materials depends on several factors such as weight (preference for polyethylene : weight reduction of one third), heat resistance (preference for para aramid), sensitivity to humidity (preference for polyethylene)...

From time to time, research brings new materials with properties deemed to surpass those of current products. Some of them seem to be promising, such as carbon nanotubes, for example. Nevertheless, nowadays, the most used materials are the fibers we mentioned above.

• Tensile and Shear Modules

A few lines on this subject to understand the strength of the fibers and their weakness.

Tensile modulus

This characteristic defines the mechanical tensile strength of the fiber, i.e. when stretched in the direction of its length. For example, for the same weight, a para-aramid fiber rope has a tensile strength five times greater than that of a steel rope. Polyethylene fibers are said to be ten times stronger than steel. It is this particularity that allows the stopping of a projectile by a ballistic pack, provided that the fibers can be solicited in traction, i.e. according to their highest modulus.

Fiber in tension

Shear modulus

It determines the mechanical resistance when the fiber is stressed perpendicular to its length, without the possibility of moving. This modulus is low for both types of fibers. This explains their poor performance in stopping projectiles or sharp objects (arrows and crossbow bolts, knives...). It is also understandable that these fibers must be allowed relative freedom to move backwards on impact, allowing them to be loaded at their highest modulus, in tension.

Fiber in shear

Traction, shear synthesis

Fibers stressed in shear	Fibers stressed in tension

Tensile modulus, shear modulus : the consequences

The notions of tensile and shear moduli being clarified, it is easier to understand that a bulletproof vest, as its name indicates, is intended to stop bullets. It will therefore be in difficulty when faced with sharp projectiles.

III-1-2 - FIBERS, THREADS, FABRICS, PLIES

• The two main fibers: para aramid and polyethylene fibers

Below, two pictures showing a yarn made from para aramid fibers (Kevlar®, Twaron®,...) and polyethylene (Spectra®, Dyneema®,...). Para aramid fibers are yellow and polyethylene fibers are white. These fibers do not dye well, so their respective color allows to identify them.

Para aramid fibers (Kevlar®, Twaron®...)	Polyethylene fibers (Spectra®, Dyneema®...)

From the fibers, threads are made that will allow the realization of ballistic fabrics that are called "plies". These are the constituent units of the ballistic pack. To create these ballistic fabrics, two methods are mainly used: weaving for para-aramid fiber yarns which lend themselves well to this method and juxtaposition (unidirectional mode) for polyethylene fiber yarns which lend themselves less well to the weaving method. In the case of juxtaposition, a ply consists of two fabrics superimposed at 90 degrees. This gives a mechanical strength equivalent to the woven ply (see the two images below). The technology evolves and other processes can appear. They always go in the direction of a greater effectiveness or a better comfort.

Weaving - Kevlar®, Twaron®	Unidirectional - Spectrashield

Kevlar® fabric	Spectra® fabric...Note the 90° cross structure

The level of protection depends on the number of fabric plies

The superposition of the plies, in variable number, allows to adapt the protection to the level of the threat. The plies are sewn together in such a way that a needle does not pass through all the plies. This avoids the creation of a zone of weakness.

• Surface density of energy

It is the ratio between the quantity of energy and the surface. In the International System, it is expressed in joules per square meter (J/m²).

In terminal ballistics, it is the ratio between the kinetic energy of the projectile and its interaction surface with the target. It can be quite complicated to define, given that it is likely to vary throughout the interaction with the target, which is what is sought with ballistic protections. When an agreement is found to define the interaction surface, by calculating it for example from the calibre of the projectile, this data is used to characterize the penetration power of this projectile. There is nothing to prevent it from being expressed in a more meaningful way for the ballistic expert, in joules per square millimeter (J/mm²).

For a given kinetic energy at the moment of impact, the larger the interaction surface, the lower the surface density and the easier it is to stop the projectile. This is what we see. It is therefore clear that the more a projectile is deformed during its interaction with the protection, the greater the interaction surface and the better it is stopped.

The more fibers are involved, the easier it is to stop the projectile. Thus, the deformation or even fragmentation of the projectile on or in the protection is a preponderant factor in stopping it. This is the main characteristic of ballistic protection, including armor. To be effective, a ballistic protection must deform, break, "hurt the projectile" say the armor specialists.

Projectile stopped in Twaron® plies

In a flexible ballistic pack, the first plies are mainly stressed in shear while the following ones are stressed in tension.

To stop a projectile, the net principle is used.

The first plies are stressed in shear. The following ones are in traction, they play the role of a net.

III-2 - LIMIT THE BACK TRAUMA

Although the projectile is stopped, its kinetic energy and momentum are transmitted to the ballistic protection, which moves violently backwards, and then to the body region opposite the impact. This phenomenon can cause trauma to the impacted area. Indeed, the body region behind the impact undergoes in turn a brutal acceleration, creating a deep deformation in the form of a dynamic cone. The latter can generate more or less significant lesions, identical to those caused by the impact of a blunt object, such as a defensive rubber bullet for example.

Formation of the dynamic cone Ballistic gelatin at 10% and 4°C rubber

This injury phenomenon must be reduced to a minimum, without affecting the proper functioning of the protection. Indeed, in order for the fibers to be solicited according to their highest modulus, i.e. in traction, they must be able to move towards the rear. The solution generally adopted is to add an anti-trauma material to the rear of the ballistic pack. This anti-trauma material, inserted between the ballistic pack and the body, acts as a shock absorber and energy diffuser.

Diagram of the transmission of the shock due to the impact. Without anti-trauma material.	Diagram of the transmission of the shock due to the impact. With anti-trauma material.

• Anti-trauma materials

There are several types. We can note, for example :

1 - Wadding ;

2 - Foams ;

3 - Honeycomb structures.

 

Different types of anti-trauma materials

The difficulty lies in the choice of an anti-trauma material that has good energy absorption/diffusion at the deformation speeds imposed by the projectile. Since most materials are usually tested in quasi-static mode, it is necessary to evaluate them in dynamic mode by subjecting them to deformation speeds identical to those they would experience in practice.

In certain configurations, the anti-traumatic role is ensured by inserting plies with greater rigidity into the ballistic pack.

Finally, new technologies feature materials that stiffen when subjected to mechanical impulses or high strain rates.

It is interesting to keep in mind that materials that show excellent behavior in the laboratory can lose their characteristics when subjected to the constraints of regular use over time.

The ballistic and anti-trauma packs made, they are enclosed in a waterproof case.

The ballistic pack and the anti trauma are inserted in a waterproof cover.	The cover is welded to ensure watertightness.

From then on, the ballistic pack will be called the set consisting of the ballistic material, the anti-trauma and the waterproof cover.

This set is, in turn, inserted into a protective cover that forms the outer, visible part of the bulletproof vest.

The complete ballistic pack is inserted in the in the outer cover.

To be noted

It may be necessary to remove the ballistic pack from the outer cover. This operation is planned, therefore easy. You may, in fact, wish to clean the outer cover, check the integrity of the ballistic pack and especially of its waterproof cover. When reassembling, make sure to put the pack back in the right direction, so that the anti-trauma material is facing the inside (towards the body) and not the outside. The direction of assembly is indicated on the pack.

III-3 - RIGID BALLISTIC PLATES

To stop the more powerful projectiles fired by long guns, rifles, assault rifles, ballistic plates are used which have an increased stopping power. Depending on the level of ballistic protection required, we use plates made of the same materials as the soft packs, i.e. para-aramid fibers (Kevlar®, Twaron®...) or polyethylene (Spectra®, Dyneema®...). In this case, the plies are coated with resin and the whole is hot pressed. The resin coating and pressing phases are crucial to ensure that the sheets hold up well over time and avoid delamination. If an even higher level of protection is desired, and in particular to stop perforating projectiles, other materials such as ceramic are used, in homogeneous plates or in plates made up of elements of various shapes included in a matrix. This last configuration allows to limit the cracking of the plate which would lead to a loss of efficiency in case of multiple impacts.

Some ballistic protections are only made of a front and rear plate inserted in a chasuble or plate holder.

Due to their rigidity, ballistic plates require the use of an anti-trauma material.

Ballistic plates, one in polyethylene.

An example of the good "work" of a ballistic plate

The video below shows the ceramic back plate of a Ukrainian fighter that perfectly protected him from two impacts. He is safe and can even continue his mission.

Advice

If your hosts offer or require you to wear ballistic protection while on a mission in a theater of operations, if there is a plate, make sure it is a ballistic plate. We've seen used ballistic vests where the ballistic plate has been replaced with a wooden plate. So trust your hosts, but check anyway!

IV -  BALLISTIC PROTECTION LEVELS - STANDARDS

There are different standards in the world defining the levels of ballistic protection (European, German, English, Russian, American...). Each of these standards is defined according to the aggressive context in which the wearer of the bulletproof vest is supposed to evolve. This explains the variations that appear between different countries, even if we could wish for a real uniformity at the European level.

Whatever their origin, the texts define classes of protection corresponding to increasingly aggressive ammunition. They also establish strict test protocols. Some of these standards take into account a single impact, others multiple impacts and, in this case, impose a precise distribution of these impacts on the test specimen.

The back deformation that can give an indication of the blunt trauma caused by the impact is taken into account. Depending on the country, it is evaluated on plastiline, a material composed of mineral powder (calcium carbonate) mixed with small proportions of industrial waxes and mineral oil. On this material, which is calibrated before the tests, the maximum tolerated indentation also varies according to the country, from 20 to 25 mm for Europe and up to 44 mm for the United States. This difference for the United States is due to the fact that the .44 Magnum caliber is taken into account. At the French Ministry of the Interior's Centre d'Études et de Recherche, which later became the Centre Technique de la Sécurité Intérieure, we were among the first, with the DGA, to initiate the measurement of the dynamic cone of deformation on 10 and 20% ballistic gelatin using a high-speed camera.

These various standards are easily found on the Internet. Below is a link to one of the oldest organizations to create a standard, the National Institute of Justice:

https://nij.ojp.gov/topics/equipment-and-technology/body-armor

For a synoptic view of the different standards, please consult the table proposed by DSM Dyneema.

To be noted

Ballistic standards are not fixed, they can evolve, following the evolution of the threat.

• Decrypting a standard

A ballistic standard is a technical document in which each piece of information is important. It describes precisely the protection characteristics of the product concerned, tested according to a precise and detailed protocol. A careful reading also allows to deduce the limits of a protection.

Let's take an example with the N.I.J. 0101.06 standard of which we present, below, an extract of the classification table. You can access the entire table by following the link above.

First part of the N.I.J. standards table Note the precise description of the test protocol.

This part of the table is instructive because it sheds light on a number of points that must be considered when hearing that a protection meets a standard.

Case study

You are fitted with a bulletproof vest, or it is offered to you for purchase. It is a discreet vest, equipped with a soft ballistic pack. It is rightly claimed that it is made to NIJ standards and protects against the most common handgun calibers in Europe: .38 Special, 9mm Parabellum and .357 Magnum. If you are a novice, no one can blame you, you will leave satisfied with your vest without asking any embarrassing questions to your supplier. After reading the following pages, this will no longer be the case. So let's study the chart.

It can be seen that it is subdivided, from top to bottom, into five classes: IIA, II, IIIA, III, IV (we say two A, two, three A, etc.), each of these classes corresponds to an increasing level of protection against increasingly aggressive projectiles. The levels of protection start with class IIA, which is specific to handguns, and culminate with class IV, which corresponds to 7.62 mm calibre armour-piercing projectiles. There was a time when the table began with class I which concerned the following projectiles:

- 22 Long Rifle lead bullet, m = 2,6 grams, speed = 320 m/s ;
- 9 mm short FMJ, m = 6,2 grams, speed = 312 m/s.

This Class I was not expected to generate much interest, hence the decision to start at Class IIA.

Now we get to the important details.

• Type of projectile

For each class a number of parameters are specified :

• Type of projectile : for example, for IIA class : 9 mm FMJ-RN i.e. Full Metal Jacketed – Round Nose ;


• Mass of the projectile : 8 grams ;


• Manufacturer's reference : Remington 23558. Important information because it allows to know all the characteristics of the projectile. For example, the nature of the materials used to manufacture the core and jacket and the thickness of the latter. All these factors influence the penetration and perforation capacity of the projectile. We remember the difficulties we encountered with the Norma 19022 9 mm projectile compared to other 9 mm parabellum ammunition ;


• Speed : speeds are specified with a relatively severe tolerance margin ;


• Conditioned / new Armor : two cases are considered. Tests on a new vest at ambient temperature (new Armor) or on a vest (conditioned Armor) which has been placed, after passage in a climatic chamber, in particular conditions of use of temperature. In this case, a drop in performance is accepted.

The importance of the type of projectile in its classification also appears for the .357 Magnum caliber which, depending on the case, is classified II or IIIA.

• Projectile speed

Depending on its speed, a projectile can go from one class to another.

This is the case with the Remington 23558 9mm FMJ-RN projectile weighing 8 grams, which is classified as Class IIA or II depending on whether it is tested at a velocity of 373 +/- 9 m/s or 398 +/- 9 m/s on new protection.

• Shooting parameters

The complete table specifies the number of shots that a specimen must withstand as well as the different angles of incidence under which the shots must be performed.

Summary

We do not think it is necessary to go any further to demonstrate to the reader the relative complexity of the subject and that, faced with a summary assertion claiming that such and such a bulletproof vest stops such and such a caliber, it is not inappropriate to ask for more details.

IV-1 - BALLISTIC PROTECTION LEVELS IN PRACTICE

Knowing how to read a standard is helpful. However, you don't usually have this document when you are issued a bulletproof vest. That's why it's useful to have some reference points.

Stopping handgun projectiles

Generally speaking, soft body armor is intended to stop ammunition fired from a handgun. Handguns are defined as pistols and revolvers with barrel lengths in the range of four to six inches, or 10 to 15 centimeters. Beyond these barrel lengths, velocities are likely to be off the charts. Beware also of uncommon ammunition such as the french THV 3.5 g, 600 m/s bullet that requires an additional plate to be stopped. It is true that the THV is no longer on the market and, in order to carry out tests, we were obliged to manufacture it. However, there may be some left in the back of the drawer. Beware also of the 7.62 mm Tokarev or the 7.63 Mauser which, after passing through a 50 cm block of ballistic gelatin, is not stopped by a soft ballistic pack. Apart from these particular and very rare cases, a soft body armor (discreet, light, etc.) stops the most common projectiles fired by a handgun: .38 Special, 9 mm Parabellum, .357 Magnum. The same applies to the .40 S&W caliber, which is not very common in our part of the world, as well as the .45 ACP caliber, which is becoming rarer as time goes by.

Stop more powerful projectiles - Add a layer

When one wishes to increase the level of ballistic protection, one adds, in front of the flexible pack, a rigid plate capable of stopping a more powerful projectile. We have seen the rigid plates above, so we will not return to them. It is well understood that the increase in the level of protection only concerns the surface covered by the additional plate. An example is the 7.62 x 51 mm (.308) or 5.56 x 45 mm (.223 Remington) ammunition with a lead core and brass liner, which are typically used by NATO forces*. It should be noted that the projectiles in the armies of the former Warsaw Pact, i.e. the 7.62 x 39 mm AK 47 cartridge and the 5.45 x 39 mm AK74 ammunition, both have a mild steel core and are capable of perforating para-aramid or polyethylene plates, at least at close range. The levels of protection are adapted to the threats likely to be encountered in different theaters of operation.

* The term "ordinary bullet" corresponds, or at least corresponded, to the projectiles in the basic equipment of the NATO combatant. It was the same for France when it was not part of this organization. We used, then, the 7.5 x 54 mm ammunition. For the armies of the Warsaw Pact countries, the ordinary AK 47 and AK 74 projectiles had a soft steel core which made them more armour-piercing than the NATO ones. It should be noted that these projectiles are still in use despite the breakup of the "Eastern Bloc". Nowadays, due to the almost systematic equipment of combatants with ballistic protection, this distinction is less clear and the "mixing" of ammunition has practically become a rule.

• Know at a glance the level of protection of a bulletproof vest

The level of ballistic protection is indicated on a label placed on the ballistic pack, whether it is soft or hard. On this label is various information such as the manufacturer's name, type of material used, lot number, and most importantly, the weights, velocities and types of projectiles that are stopped. The reason this label is there is so that it can be read !

Information label It must appear on every ballistic pack.

During our conferences, we were regularly asked a question: are there any projectiles that are not stopped by my bulletproof vest? Our answer was always the same: consider that your vest does not stop any projectiles except those listed on the information label of the ballistic pack. Any attempt to estimate the piercing capacity of one round versus another based on kinetic energy is risky. Many other factors come into play, such as the caliber, the thickness of the projectile jacket, the material of which it is composed...

IV-2 - WEAKNESSES IN THE ARMOUR

Body armor protects the areas it covers. This is obvious for the front and rear faces. We often tend to forget about the profile. It is mainly on the sides that the defects of the armor are located. This lack of protection occurs when the front and rear ballistic packs, often due to a poor choice of size, overlap poorly or not at all, leaving an unprotected area. If this problem can be remedied by a better adjustment of the protection, there is a deficiency that cannot be remedied, at least on discrete vests. It is the shoulder and arm passages. In this regard, thinking that the shoulder muscles can provide some protection when hit in profile, as we have heard, is a bad idea. Flaws in the armour exist, they are unavoidable and we must be aware of them to avoid exposing them.

Unprotected area, in red.	One solution: shoulder protectors. Not possible on discreet vests.

The more body armor covers the maximum amount of body surface area, the less likely it is that flaws will occur. It is therefore important to choose the right size. We had the mission to appraise a bulletproof vest that, during a three-quarter profile shot of a 12-gauge lead charge, did not save the life of the person wearing it. The impact was to the edge of the pectoral region. A part of the lead charge was stopped by the vest the other part penetrated in front of the armpit and reached the heart. The conclusions of the expertise were that the bulletproof vest could stop the pellets but that it was too small compared to the wearer's size.

While ballistic protection was offered in several sizes, we found that users of bulletproof vests often chose a minimalist solution for reasons of comfort, wanting to satisfy an administrative obligation rather than a need to protect themselves. A choice that can have serious consequences.

V - AGEING AND LIFE SPAN OF BALLISTIC PROTECTIONS

Fiber manufacturers guarantee the mechanical characteristics of their products for a specific period of time, usually five years. There are probably many reasons for thi s: security, legal and, presumably, commercial. This time limit therefore also affects bulletproof vests.

• Temperature and hygrometry

At the Centre Technique de la Sécurité Intérieure, accelerated ageing tests in a climatic chamber were carried out on bulletproof vests. Thermal and hygrometric cycles were produced for a simulated period of five, ten and fifteen years. At the end of each period, shots were fired on samples and showed no degradation in performance.

• Mechanical fatigue

Bulletproof vests were installed on robotic busts that reproduced the movements of a human bust: bending, twisting. They demonstrated a good resistance to these repetitive mechanical constraints.

Advice

A bullet-proof vest is therefore very durable over time. If one is somewhat suspicious of the reliability of accelerated aging tests, one should know that there is a secondary market for ballistic protection. Many states donate, as aid to less fortunate countries, bulletproof vests that, although they have reached the end of their administrative life, are still functional and seem to satisfy users.

Although a bullet-proof vest has a very good resistance to the mechanical, thermal and hygrometric constraints to which it is subjected during its use, it is good to remember that taking care of it is a guarantee of safety. In particular, we should avoid:

• To subject it to high temperatures. Be careful with the back of the vehicle, especially in summer ;


• To place it without care in a luggage and risk to crumple it (tote bags). Repeated folding of the ballistic pack weakens it at this point. It should be stored flat or in a closet ;


• To store it wet, even if the ballistic pack is considered waterproof.

VI - ERGONOMICS AND PROTECTION : A MATTER OF COMPROMISE

The main criticisms of body armor are weight, bulk, rigidity and heat.

It should be noted that these factors are taken into account by both designers and institutional buyers. Institutional buyers require, during calls for tenders, the respect of specifications or special technical clauses. Suppliers must comply. Validation tests are rigorous.

• The ideal specifications

The ideal specifications are simple: to protect the wearer as much as possible while minimizing the hindrance in the accomplishment of his mission(s). These two objectives are contradictory and lead to indispensable compromises.

• Protection level and ergonomics : the opponents

The technique allows for full body protection. Just look at the protective clothing worn by deminers. It protects effectively from the shrapnel and blast of an explosive device. On the other hand, the fully equipped deminer will move over very short distances and will wear this protection for a relatively short time. This outfit is perfectly adapted to a type of mission.

The diversity of the missions of law enforcement agencies and armies leads to a de facto diversity in ballistic protection. This explains the different types of ballistic vests, from the heavy intervention vest that is worn during an assault to the discreet vest used for hours under a suit, or even the ballistic breastplate that equips a soldier on the battlefield for days on end.

•The main ergonomic constraints

Weight

The specifications or special technical clauses generally impose a maximum weight, often very restrictive. The art of the designer will be to obtain a balance between the surface to be protected, the level of protection required, i.e. the quantity of ballistic material, and the type of material to be used (para-aramids, polyethylene...).

Bulkiness

Ergonomic constraints impose the possibility to perform the gestures necessary for the proper execution of missions: running, crouching, sitting easily in a vehicle, using one's weapon. During tests, personnel equipped with ballistic protection can be asked to perform typical routes.

Heat

Although heat, considered as an inevitability, is generally not taken into account specifications, it is nevertheless a factor to consider in terms of user comfort. Body heat is poorly evacuated. The same is true for perspiration. Despite the use of materials that are supposed to reduce this inconvenience, a bullet-proof vest is hot, which naturally leads the body to sweat. It should be noted that there are undergarments designed to promote air circulation between the body and the ballistic protection.

Keep in mind that there are constraints to wearing body armor and you have to accept them.

VII - CONCLUSION

Since the emergence of the "zero death" concept, the wearing of ballistic protection has become widespread on the battlefield. The same is true for law enforcement, where bulletproof vests are an integral part of individual equipment. In this respect, the female morphology is taken into account.

To be effective, ballistic protection must match the threat level and the wearer's body type.

The high-intensity conflict between Ukraine and the Russian Federation has shown that, while the concept of "zero deaths" is wishful thinking, the wearing of ballistic protection significantly reduces the number of injuries and deaths.

The fact remains that, like seat belts in the automobile industry, if individual ballistic protection saves lives, it must not lead to a feeling of invincibility.

A bulletproof vest is a compromise between protection and ergonomics. No ballistic protection is perfect, but keep in mind that a bulletproof vest is useful and works, as shown in the video below.