Accurate pressure measurements during underwater detonations are critical for the protection of structures and mitigating impacts to fish and marine mammals. Current guidelines that limit underwater pressures are based on past studies, many of which used sample rates of 48 and 65 kS/s (48,000 and 65,000 samples per second). These sample rates may be insufficient to accurately record high frequency, sharp rise time blast pressures. As such, pressure thresholds associated with fish and marine mammal injury or mortality may be underestimated, calling into question the pressure and sound pressure level guidelines that govern underwater blasting today.Open-water blast pressures were measured using up to 12 pressure sensors during small-scale tests with blasting caps at cube-root scaled distances (CRSD) ranging from 16 to 145 ft/lb1/3 (6 to 57 m/kg1/3). Sample rates ranged from 5 to 5,000 kS/s. Recommendations were made for the minimum sample rate necessary to accurately record peak pressures. Peak pressures increased with sample rate up to a maximum between 1,200 and 2,500 kS/s. However, a rate of 5,000 kS/s is recommended to accommodate the fastest documented rise times of 1 μs at the pressure front.Pressure data for unconfined detonations were compared to full-scale rock excavation and pier demolition rise times to establish minimum recommended sample rates of 200 and 600 kS/s, respectively. These rates are based on the fastest observed rise times of 30 μs (microseconds) for rock and 9 μs for pier.
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