| Metric | High-Order Detonation | Low-Order Deflagration | | :--- | :--- | :--- | | | 240–260 dB | 200–220 dB | | Rise Time | < 1 µs | 5–50 ms | | Dominant Frequency | 100 Hz – 10 kHz | 20 – 500 Hz | | Injury Zone (PTS) | 1 – 3 km radius | 50 – 300 m radius | | Behavioral Disturbance Zone | 10 – 50 km radius | 500 m – 3 km radius | | Risk of Barotrauma | High (lung/ear rupture) | Negligible | | Risk of Physical Displacement | Very High (mass strandings) | Low |
In response, the maritime community has turned toward as a "quieter" alternative. This transition is supported by a growing body of scientific research focused on the underwater acoustic characterisation of these events to quantify their reduced environmental footprint. Understanding the Mechanisms: Detonation vs. Deflagration | Metric | High-Order Detonation | Low-Order Deflagration
Deflagration acts as a low-pass filter. The combustion process cannot generate the high-frequency harmonics associated with a shock wave. Acoustic measurements of deflagrations (e.g., from the SERDP Project MR-2434) show that >95% of the acoustic energy is confined to frequencies below 500 Hz, with a peak often between 20 and 150 Hz. This infrasonic/low-frequency content propagates over longer distances but causes less direct physiological damage to fauna. Deflagration Deflagration acts as a low-pass filter
is a subsonic combustion process (flame front velocity typically < 1000 m/s, often < 100 m/s). In a controlled deflagration (used in commercial "low-order" systems like the RA-9 or EOD Robot Deflagration Systems), the energetic material is heated rapidly but not shocked into detonation. The burn propagates through the explosive filler via thermal conduction. The resulting gas release is relatively slow, generating a pressure pulse that lacks a distinct shock front. Underwater, this manifests as a longer-duration, lower-amplitude "thump" rather than a crack. this manifests as a longer-duration