What Is Blast Overpressure and How to Measure It
When an explosive goes off, the energy is released almost right away. A high-pressure wave of air moves outward at supersonic speed. We call that wave “blast overpressure” when it is higher than normal atmospheric pressure.
Blast overpressure is not just a physics idea for people in the military, combat engineers, explosive ordnance disposal technicians, and anyone who works near weapons systems or demolition charges.
It is a real risk at work, and there are documented effects on hearing, lung function, and brain health, some of which may not show up until years after the exposure.
This article explains what blast overpressure is, how blast waves behave, what they do to the human body at various pressure levels, and how researchers and military organizations measure and manage blast overpressure exposure today.
What Is Blast Overpressure?
Blast overpressure (BOP) is the rapid, sudden rise in air pressure exceeding normal atmospheric levels caused by high-explosive detonations or weapon firing. Normal atmospheric pressure at sea level is approximately 14.7 PSI (101.3 kPa).
Any pressure above that baseline, created by an explosion’s shock wave, is the overpressure. When researchers and military standards refer to a blast exposure of 4 PSI, they mean 4 PSI above atmospheric, not 4 PSI in total.
According to Wikipedia’s Overpressure entry, it receives particular attention when measuring the effects of explosive detonations, nuclear weapons, and thermobaric devices.
The U.S. Army Medical Research and Development Command’s Blast Injury Research Coordinating Office (BIRCO) explains the process very well: an explosion compresses the air around it almost instantly, sending out an overpressure wave at supersonic speed from the point of detonation.
After that comes a zone of negative pressure, or underpressure, which pulls things behind the wave. After the negative phase is over, the pressure goes back to normal. For a full overview, check out the BIRCO Science of Blast page.
The Physics of a Blast Wave
The Friedlander Waveform
The Friedlander waveform is the idealized pressure profile of an air blast in a calm, open space. This waveform is the basis for measuring blast overpressure.
According to the U.S. Army medical reference on blast physics and mechanisms, the Friedlander waveform has the following stages:
- Shock front arrival: The pressure goes up almost instantly from the ambient level to the peak level. Rise times are measured in millionths to billionths of a second.
- Positive phase: Pressure drops off quickly from the peak back to the normal level. This is where most of the harmful energy comes from.
- Negative phase (underpressure): The pressure goes below the ambient level before going back to the baseline. This phase is usually longer than the positive phase but not as strong.
The area under the pressure-time curve, which takes into account both the size and the length of the blast wave, is what gives it its impulse.
Impulse is often a better predictor of structural damage than peak pressure alone because many structures react to the total energy of the load instead of just the peak.
Reflected and Complex Waves
A free-field blast wave is rarely what people experience in practice. According to the BIRCO Science of Blast, blast waves reflect off hard surfaces and can be amplified two to nine times as a result of wave reflection. Someone standing between a blast and a building will typically suffer more severe injury than someone in open terrain.
When there are many wave fronts in a small space, like inside a car, in a tunnel, or on city streets, it makes it much harder to understand and measure blast overpressure.
The ground reflection changes the primary wave’s properties, even in open fields. Because of these effects, real-world blast exposures are always more complicated than what the Friedlander model says they should be.
How Distance Affects Blast Overpressure
Blast overpressure diminishes rapidly with distance from the detonation point. According to FEMA’s explosive blast guidance, an explosion can be visualized as a bubble of highly compressed air that expands until reaching equilibrium with the surrounding atmosphere. As the bubble expands, the pressure at any given point drops sharply.
Military engineers use scaling laws, like the Hopkinson-Cranz scaled distance law, to figure out how much blast overpressure there will be at a certain distance from an explosive charge of known weight.
To get the scaled distance, you divide the real standoff distance by the cube root of the weight of the explosive charge. These calculations are used to plan for safety, figure out how far away from the explosion to be, and design buildings that can withstand blasts.
Key Blast Overpressure Parameters and Units
The following table summarizes the primary parameters used when measuring and reporting blast overpressure, drawn from U.S. Army and scientific sources.
| Measurement Unit | Description | Typical Threshold |
| PSI (pounds per square inch) | Most common unit in U.S. military applications | 2-4 PSI: current DoD training limit |
| kPa (kilopascals) | Standard SI unit used in scientific research | 14-28 kPa: equivalent to 2-4 PSI |
| Peak Overpressure | The highest pressure was recorded at the shock front | Determines immediate damage potential |
| Impulse (psi-ms) | Pressure integrated over time (duration) | Determines structural and biological damage |
| Positive Phase Duration | Time the pressure stays above ambient | Milliseconds for most blast events |
| Friedlander Waveform | Idealised mathematical model of a blast wave | Used for modelling and calibration |
Source: U.S. Army blast physics reference; Fort Leonard Wood Blast Overpressure overview; FEMA explosive blast guidance
How to Measure Blast Overpressure
Accurate blast overpressure measurement is technically demanding. The pressure events are extremely brief, measured in microseconds to milliseconds, and the magnitudes can range from fractions of a PSI in low-level training environments to thousands of PSI near the detonation point of large charges.
Any measurement system must respond fast enough to capture the shock front, survive the thermal and mechanical environment of the blast, and produce data that can be reliably interpreted.
Piezoelectric Pencil Probes
The most widely used instrument for free-field blast pressure measurement is the piezoelectric pencil probe. According to the U.S. Army Research Laboratory (ARL) technical note on pencil probe utilization, pencil probes are slender cylindrical instruments designed so that the sensing element is mounted flush with the body, with the probe’s long axis aligned parallel to the direction of shock wave travel. This side-on orientation measures incident (free-field) overpressure rather than reflected overpressure.
The sensing element inside a pencil probe is a piezoelectric crystal, typically quartz, mounted in an Invar (nickel-iron alloy) housing.
When the shock wave compresses the crystal, it generates an electrical charge proportional to the applied pressure. That signal is conditioned by an integrated circuit (ICP) amplifier and recorded by a data acquisition system. The output, typically in millivolts, is converted to pressure units using the sensor’s calibration factor, which is provided by the manufacturer and verified periodically.
PCB Piezotronics manufactures the most commonly used pencil probe series in U.S. defense applications.
The PCB Series 137 ICP blast pressure sensors are available in pressure ranges from 50 PSI to 1,000 PSI. The ARL uses models 137A23 (50 PSI range), 137A22 (500 PSI range), and 137A21 (1,000 PSI range) depending on expected pressure magnitude. Selecting the right range is critical: an undersized sensor will clip the peak overpressure, losing the most important data point, while an oversized sensor will produce poor resolution in the signal.
Sensor Orientation and Measurement Accuracy
A 2025 study published in Scientific Reports identified sensor orientation as a significant source of variability in blast overpressure data. The study, conducted by researchers Nicholas W. Kuehl and Catherine E. Johnson using C4 explosive, found that the orientation of a sensor relative to the blast source (head-on, side-on, or oblique) substantially affects the recorded pressure value.
To address this, the researchers developed and validated a method using three sensors mounted in orthogonal orientations (X, Y, and Z planes) and combining their readings using a root mean square (RMS) calculation to produce a single representative value that is independent of orientation.
This approach is now being explored for both laboratory testing and field measurement of blast exposures on military personnel.
Wearable Blast Gauges
For monitoring personnel exposure during training and operations, wearable blast gauges have been developed as an alternative to fixed pencil probes.
A study from the U.S. Army Combat Capabilities Development Command (DEVCOM) Armaments Center evaluated wearable sensors from BlackBox Biometrics (B3) by comparing their readings to conventional pencil gauges in a confined blast environment.
The wearable gauges are wireless units that can be mounted on a soldier’s helmet, body armor, or other locations, allowing exposure data to be recorded during actual training or combat operations.
The study found that sensor placement and orientation still affect readings, and that wearable units have limitations compared to precision pencil probes. However, for tracking cumulative occupational exposure over time, wearables are practical where fixed instrumentation is not possible.
Shock Tubes for Laboratory Calibration
Shock tubes are laboratory devices used to generate controlled, repeatable blast waves for research and sensor calibration.
A controlled pressure is released through the tube, generating a shock wave of known characteristics that can be used to test sensor response, validate measurement methods, and conduct biological research on the effects of blast exposure.
Research published in MDPI Sensors used shock tube testing to characterize and improve the performance of commercial PCB pencil probes, finding that standard commercial sensors have a bandwidth at minus 3 dB of approximately 30 kHz, and that optimized probes can achieve a bandwidth of 90 kHz, three times the commercial standard.
For near-field measurements where shock rise times are extremely short, this improvement is significant.
Data Acquisition and Signal Processing
Capturing a blast wave accurately requires a data acquisition system with a sample rate and recording duration matched to the expected event.
According to the ARL pencil probe technical note, the acquisition system must be configured to record at least 20% below the sensor’s baseline voltage to capture the negative phase of the pressure wave. Recording duration is typically set to at least double the expected pressure time of arrival at the farthest sensor.
Ground and air shock are documented sources of contamination in blast pressure data. Vibrations from the blast can travel through the sensor fixture and create false signals.
The standard mitigation is to isolate the probe from its mounting fixture using a vibration-damping material such as ISODAMP between the probe and the support structure.
Blast Overpressure Effects on Humans
The human body can tolerate relatively low blast overpressures without injury to most organ systems.
However, certain structures, particularly the hollow organs (ears, lungs, sinuses, and gastrointestinal tract), are extremely sensitive to the rapid pressure changes a blast wave causes.
According to the U.S. Department of Veterans Affairs research on primary blast brain injury, blast overpressure is measured in PSI or kPa, and research has established clear pressure thresholds for various injury outcomes.
Blast Injury Pressure Thresholds
The following table summarizes documented human injury thresholds, drawn from Wikipedia’s Overpressure article, the U.S. Department of Veterans Affairs, and the U.S. Army blast physics reference.
| Overpressure Level | Human Effect |
| 5 psi (34 kPa) | Eardrum rupture in ~1% of exposed individuals |
| 7.3 psi (50 kPa) | Eardrum rupture; potential lung injury threshold |
| 14.5 psi (100 kPa) | Pulmonary hemorrhage begins |
| 15 psi (103 kPa) | Lung damage threshold |
| 21.7 psi (150 kPa) | Progressive lung injury likely leading to death |
| 35-45 psi (241-310 kPa) | 1% fatality rate among exposed personnel |
| 45 psi (310 kPa) | Eardrum rupture in ~99% of exposed individuals |
| 55-65 psi (379-448 kPa) | 99% fatality rate among exposed personnel |
Sources: Wikipedia Overpressure; VA Primary Blast Brain Injury; U.S. Army blast physics reference
Four Categories of Blast Injury
The DoD’s Blast Injury Research Coordinating Office classifies blast-related injuries into five mechanism categories (primary through quinary), as detailed in a PMC systematic review of blast-related mild TBI. The most clinically relevant categories are:
- Primary blast injury: Caused directly by the overpressure wave itself. Affects hollow organs. Lung damage (pulmonary barotrauma), eardrum rupture, gastrointestinal injury, and blast-induced traumatic brain injury (bTBI) are all primary blast injuries.
- Secondary blast injury: Caused by fragments and debris propelled by the explosion. Penetrating wounds, lacerations, and embedded fragments fall in this category.
- Tertiary blast injury: Caused by the blast wind physically throwing a person against a surface. Blunt trauma, fractures, and acceleration-deceleration brain injuries occur this way.
- Quaternary blast injury: Burns, crush injuries, and exposure to toxic gases or chemicals from the explosion fall in this category.
Blast Overpressure and Traumatic Brain Injury
The most significant emerging concern around blast overpressure effects on humans is its relationship to traumatic brain injury (TBI), particularly when exposures are repeated over a career. According to the U.S. Army Medical Research and Development Command (USAMRDC), approximately 80% of injuries sustained by warfighters in Operation Enduring Freedom and Operation Iraqi Freedom were caused by blast overpressure shock waves. A VA study reported nearly 414,000 service members sustained a TBI between 2000 and late 2019.
Blast-induced TBI is often called an ‘invisible injury’ because it produces no visible external trauma and may not appear on routine medical imaging. The VA explains that energy from the shock wave is transmitted into the brain directly, causing injury through mechanisms distinct from the physical impact injuries that cause conventional TBI. This has led to the creation of a specific ICD-10 diagnostic code for primary blast injury of the brain.
Research published in Scientific Reports found that blast overpressure disrupts the blood-brain barrier (BBB), with significant permeability changes occurring at 70 kPa (10.2 PSI) and above. This BBB disruption occurs immediately after the blast, peaks at approximately four hours, and returns toward normal within 24 hours. The frontal cortex showed the greatest degree of disruption in these studies.
Low-Level Blast: The Hidden Risk
Beyond high-level combat blasts, there is growing concern about cumulative exposure to low-level blast overpressure during training. Soldiers who regularly fire heavy weapons, set demolition charges, or work in breach roles accumulate blast exposures that individually fall below established injury thresholds but may cause progressive neurological damage over time.
A 2024 PMC study on neurological effects in Special Operations personnel found elevated neuroinflammatory markers in brain-derived extracellular vesicles in operators with repeated low-level blast exposure, even in the absence of diagnosed TBI. A 2025 PMC longitudinal study in the Millennium Cohort Study found that both high-level and low-level blast exposure during military service were associated with increased risk of TBI-related diagnoses after separation from service, supporting the implementation of occupational blast surveillance systems.
Current DoD Policy and Blast Overpressure Thresholds
The U.S. Department of Defense has significantly strengthened its blast overpressure policy in recent years. According to the Fort Leonard Wood Blast Overpressure article, the November 2022 DoD interim guidance established a limit of 4 PSI for single blast overpressure exposures and recommended no more than 2 PSI during training operations with multiple exposures.
On August 8, 2024, Deputy Secretary of Defense Kathleen Hicks issued a formal Policy Memorandum for Managing Brain Health Risks from Blast Overpressure, as cited in the DoD Warfighter Brain Health Initiative report. The memorandum acknowledged documented adverse effects on brain health and cognitive performance from both acute and chronic blast overpressure exposures, including headache, decreased reaction time, attention difficulty, and memory loss.
The memorandum identified specific military occupational specialties at elevated risk, including combat engineers, EOD technicians, chemical/biological/radiological/nuclear specialists, military police, and instructors for high-BOP weapon systems such as the M2A1 .50-caliber machine gun and the M136A1 AT4 anti-tank rocket.
The same policy directed the DoD to standardize blast data collection, develop wearable exposure monitoring systems, and establish tracking programs for service members in high-risk roles. The Military Health System’s Blast Overpressure resource page is the primary reference for current guidance for service members and medical providers.
Blast Overpressure Measurement in Practice: Field vs. Laboratory
Laboratory Measurement
In laboratory settings, blast overpressure is measured with a high degree of precision using calibrated pencil probes arranged at fixed distances from a controlled charge, connected to high-speed data acquisition systems. Sensors are isolated from structural vibration, cables are shielded, and multiple sensors are placed at different distances to map the pressure field.
The Hopkinson-Cranz scaling law is applied to relate measured data at one charge weight and standoff distance to predicted values at other configurations. This allows researchers to develop data from small, repeatable test charges and apply it to larger operational scenarios.
Field Measurement on Personnel
Measuring blast exposure on actual military personnel in training or operational environments requires different approaches. Wearable sensors, like those evaluated in the DEVCOM Armaments Center study, can be attached to helmets and body armor. These capture exposure data in real time and store it for later analysis.
The challenge with field measurement is that sensor orientation relative to the blast cannot be controlled, the blast environment is complex (multiple reflections, ground coupling, confined spaces), and the sensor may be subject to physical impacts that contaminate the data. The orthogonal RMS method described in the 2025 Scientific Reports study was specifically developed to address the orientation problem in field conditions.
As of 2024, the DoD is actively pursuing standardized monitoring programs to track cumulative blast exposure by military occupational specialty, as directed by the NDAA for FY 2023. The goal is to establish dose-response relationships between occupational blast exposure and specific health outcomes, a capability that does not yet exist at the scale needed to inform policy.
Blast Overpressure and Armored Vehicle Design
For defense engineers and manufacturers, blast overpressure is not only a personnel health issue. It is a core design parameter for armored vehicles, hull structures, and protective equipment.
Armored vehicle hulls must be designed to attenuate the blast wave before it reaches the crew compartment. This involves a combination of hull geometry, material selection, and energy-absorbing structures. Spaced armor, V-shaped hull designs, and internal blast liners all interact with the incoming overpressure wave to reduce transmitted pressure.
The hull parts and structural assemblies in platforms designed for blast survivability must be manufactured to precise dimensional tolerances and verified material properties. A hull with an out-of-specification weld, a plate that does not meet its armor steel grade, or a mounting structure that deforms prematurely under blast loading creates gaps in the vehicle’s protective capability. This is why defense manufacturing quality assurance and material specification compliance are not optional in blast-survivable platform development.
The same precision requirements apply to hull parts, undercarriage components, and structural assemblies in vehicles that operate in IED-threat environments. Any component in the blast load path must be engineered for the expected overpressure profile, not just the static or dynamic mechanical loads of normal operation.
Final Thoughts
Blast overpressure is a significant threat in military settings, moving faster than sound and causing hidden injuries that affect hearing, lung function, and brain health. Accurate measurements of blast overpressure are essential for managing associated risks, utilizing tools such as piezoelectric probes and wearable gauges.
The military sector is developing infrastructure for systematic data collection and standardization to enhance safety. For defense manufacturers, blast overpressure sets design and quality standards for vehicle components, demanding precision in construction to ensure crew protection against threats like IEDs.
CEW Defense emphasizes this principle in its work on hull parts, ensuring that components are built to withstand blast challenges.
Frequently Asked Questions (FAQ)
What is blast overpressure in simple terms?
Blast overpressure is the extra pressure created by a shock wave from an explosion, measured above normal atmospheric pressure. When a bomb or charge detonates, the surrounding air is compressed and pushed outward as a wave. The amount by which that wave’s pressure exceeds normal air pressure is the blast overpressure.
What unit is blast overpressure measured in?
Blast overpressure is most commonly measured in pounds per square inch (PSI) in U.S. military and engineering applications, and kilopascals (kPa) in scientific and international contexts.
One PSI equals approximately 6.895 kPa. The DoD’s current training threshold of 4 PSI is equivalent to approximately 27.6 kPa.
What is peak overpressure vs. impulse?
Peak overpressure is the highest pressure recorded at the shock front, measured instantaneously. Impulse is the integral of pressure over time, representing the total energy delivered per unit area over the duration of the blast event.
Both matter: peak overpressure determines the instantaneous force on a structure or organism, while impulse determines how much total energy is transferred. Structures with long natural periods are often more sensitive to impulse than to peak pressure.
What are the main effects of blast overpressure on humans?
According to the VA Primary Blast Injury reference and Wikipedia’s Overpressure article, blast overpressure effects range from eardrum rupture at relatively low pressures (around 5 PSI) to lung hemorrhage, progressive lung injury, and death at higher levels (14.5 to 21.7 PSI).
At sub-threshold levels, cumulative exposure is linked to TBI, cognitive dysfunction, memory loss, tinnitus, and other neurological effects.
What tools are used to measure blast overpressure?
The primary instruments are piezoelectric pencil probes, which measure free-field (incident) overpressure at fixed locations. PCB Piezotronics Series 137 ICP sensors are the most commonly used in U.S. defense testing.
For monitoring personnel, wearable blast gauges are attached to helmets or body armor. Shock tubes are used in laboratory settings for controlled testing and sensor calibration. All measurement systems require high-speed data acquisition capable of capturing events measured in microseconds.
What is the DoD’s current blast overpressure exposure limit?
The DoD’s November 2022 interim guidance set a limit of 4 PSI for single blast overpressure exposures and recommended no more than 2 PSI for repeated exposures during training, per the Fort Leonard Wood BOP article.
The August 8, 2024 DoD Policy Memorandum updated and formalized these requirements, directed tracking of cumulative exposures, and identified high-risk military occupational specialties.
What is low-level blast overpressure?
Low-level blast refers to overpressure generated by outgoing munitions during training, such as the discharge of heavy weapons, mortar fire, or breaching charges, where exposures are below the thresholds for acute injury but may accumulate over a career.
Research into special operations personnel and career breachers has found neuroinflammatory markers and structural brain changes associated with repeated low-level blast exposure, even in the absence of diagnosed TBI.
How does blast overpressure affect armored vehicle design?
Blast overpressure is a primary design parameter for armored vehicles operating in IED or artillery threat environments.
V-shaped hull designs, spaced armor, blast liners, and energy-absorbing seat systems all reduce the transmitted overpressure reaching the crew. Components in the blast load path, including hull panels, structural brackets, and undercarriage assemblies, must be manufactured to precise material specifications and inspected to ensure they perform as designed when subjected to blast loading.
