Explosive Ordnance Disposal (EOD) is an inherently dangerous field. It requires substantial protection for the specialists involved. Despite being cumbersome and causing heat fatigue, EOD suits can only provide limited protection against small explosives. Naturally, the level of protection depends on the distance from the explosive device.
EOD suits are designed to offer protection from blasts, ballistics, and thermal threats. However, they are notoriously uncomfortable and prone to causing significant heat buildup. Heavier suits are often equipped with air-conditioning systems to prevent the visor from fogging and to increase comfort.
Some might question whether an EOD suit is worth wearing when attempting to defuse a large explosive. After all, in the event of a detonation, the outcome may seem inevitable. Yet, the suit can still offer vital protection, especially if the wearer is at some distance from the device when it explodes.
A graph used to calculate the peak incident overpressure as a function of scaled distance for a TNT charge. The graph shows curves for spherical free-air blasts and hemispherical surface bursts. TNT equivalency multipliers can also be applied to obtain equivalencies for different types of explosives. (Source: ResearchGate, B. Samali et al.)
A typical scenario involves the EOD operator controlling a robot from a safe distance, often behind a corner. Explosives are then neutralized by either shooting at them or placing a small detonation device nearby. This is done when the surrounding environment permits such action. Otherwise, if detonating the device is not an option, the specialist must approach it directly to defuse it.
In such cases, wearing an EOD suit is mandatory, often due to bureaucratic regulations. A typical suit provides protection against a 500-gram TNT-equivalent explosive at a distance of one metre. The operator’s stance—whether kneeling or prone—also affects which parts of the body are most protected and the potential injuries if the device explodes.
Blast Physics
A visualization of pressure time history from an ideal explosion. The Y-axis represents overpressure, and the X-axis shows elapsed time. The initial positive pressure phase is followed by the negative phase. The areas under both curves represent the specific impulse, relative to the X-axis. (Source: ResearchGate, Manmohan Dass Goel)
A blast wave, or air shock wave, consists of a pressure front of compressed, hot gases expanding outwards at supersonic speed from the explosive’s core. This is followed by slower-moving blast winds, also known as dynamic pressure, which reverse direction as the negative pressure phase begins.
Several methods exist to calculate blast wave parameters, such as peak incident overpressure (positive pressure), its duration, and impulse. The negative pressure phase is also a key factor, particularly with thermobaric explosives.
Two classical methods for calculating blast parameters are the Kingery & Bulmash and Kinney & Graham models. The Kingery & Bulmash model is widely used today and applies to both free-air and surface blasts. Kinney & Graham is suitable for a broader range of scaled distances but requires modification with an enhancement factor for surface bursts, typically a factor of two, due to ground reflections.
Confinement and Damage
Blast loading can be categorized as either confined or unconfined. Unconfined explosions include free-air blasts, air blasts near the ground, and surface bursts. Confined explosions occur inside structures and can be classified as fully vented, partially confined, or fully confined.
When assessing blast loads on structures, several factors must be considered, including the incident pressure and dynamic components. The United States Department of Defense Blast Injury Research Coordinating Office (BIRCO) outlines five key factors that determine the extent of damage caused by a blast wave:
- The peak of the initial positive pressure wave.
- The duration of overpressure.
- The medium of the explosion.
- The distance from the blast wave.
- The degree of focusing, especially in confined spaces or near walls.
Rigid surfaces tend to amplify blast intensity due to reflections. In unconfined surface burst situations, an enhancement factor of two is often applied to calculate incident overpressure, making it seem as if the blast originated from an explosive twice the actual size.
In confined environments or near solid walls, the blast wave can intensify even further. Predicting blast propagation in urban settings is complex and typically requires numerical simulations. Nevertheless, an experienced EOD specialist can often anticipate how a blast wave will behave, considering factors like wave propagation, surface reflections, shrapnel, and safety distances.
Blast Injury Mechanisms
Blast injuries are classified into four categories: primary, secondary, tertiary, and quaternary.
- Primary blast injuries are caused by the shock wave or overpressure and affect gas-filled organs such as the lungs. Pressure differentials can also injure the bowel if air is trapped inside. Protective materials and solutions must be employed to decouple organs from blast stress.
- Secondary injuries result from fragments and shrapnel propelled by the explosion, which can cause injuries over a large distance. Buried explosives, like anti-personnel mines, create dense shrapnel from the surrounding soil, often leading to severe lower-body injuries.
- Tertiary injuries are caused by the force of the blast winds, which can throw a person into objects. Lighter individuals, such as children, are particularly vulnerable.
- Quaternary injuries include all other blast-related injuries, such as burns and the inhalation of toxic gases. Flash burns typically last only a few milliseconds but can last much longer with thermobaric weapons, where the main injury mechanism is still blast overpressure. Burns require close proximity to the explosion and are particularly difficult to treat.
The Med-Eng EOD 10 suit and helmet, both fully NIJ 0117.01 certified. This suit is considered one of the finest EOD suits available. (Source: Med-Eng)
Med-Eng: Leading in Protective Gear
Med-Eng is a global leader in EOD safety equipment, founded in 1981 and based in Canada. As part of the Safariland Group, Med-Eng has pioneered research on blast effects and developed solutions to mitigate thermal threats faced by bomb technicians, military vehicle crews, and sensitive electronics
Med-Eng’s products are trusted by military and public safety agencies worldwide. Their range includes bomb suits, robots, search and disposal tools, blast sensors, and cooling and heating systems.
In the Movies
The Med-Eng protective gear gained widespread recognition following the release of the film The Hurt Locker (2008), where the protagonist, Staff Sergeant William James (played by Jeremy Renner), wears a Med-Eng EOD 9 bomb suit. While the film’s realism is debatable, the sight of someone in an EOD suit is undeniably impressive.
Med-Eng’s current range includes the EOD 9N and EOD 10 bomb suits, both fully certified to the NIJ 0117.01 standard for public safety bomb suits. These suits provide superior blast, ballistic, and thermal protection, while also allowing flexibility and mobility.
The EOD 10, and its updated version, the EOD 10E, are considered some of the most advanced bomb suits available, trusted by professionals around the globe. Med-Eng also offers lightweight, modular suits for situations requiring greater mobility, such as military EOD operations or bomb disposal support for SWAT teams.
Beyond the Standard EOD Suit
In addition to the robust EOD 9N and EOD 10 bomb suits, Med-Eng provides more agile solutions for specific operational needs. For scenarios requiring increased mobility but less extensive protection, the TAC 6E is a preferred option. This lightweight, modular suit is designed for military EOD operators and bomb technicians supporting specialized teams like SWAT units or local bomb squads.
Given its reduced protection level, when an operator uses lightweight suits such as the TAC 6E, additional measures are necessary to guard against thermal injuries. For instance, a heavy-duty, non-flammable balaclava is often worn to protect the face, especially in the absence of a fully sealed helmet.
Scaled Distance Formula
Scaled distance is calculated using the formula Z=R/kg1/3, where R is the distance in metres from the explosion epicentre, and kg is the explosive mass in kilograms. Scaled distance is necessary to obtain peak incident overpressure and other variables from graphs.
On the Author:
Jukka Janhunen (M.Sc. Tech) graduated from Helsinki University of Technology in 2005, specializing in materials deformation and polymer technology. His main areas of expertise include terminal ballistics and ballistic protection materials. Jukka also has a keen interest in explosion physics and various other aspects of military engineering. He resides currently in Helsinki, Finland.
