Cutting underwater versus above water significantly affects noise levels, dust generation, and operating cost in abrasive waterjet operations. Each method has distinct advantages and trade-offs depending on material type, thickness, and shop requirements.

Noise Levels
Above-water cutting produces a high-frequency jet noise typically ranging from 85–100 dB at the operator position, often requiring hearing protection. The piercing action is especially loud (up to 105 dB) due to jet reflection off the material surface. Underwater cutting dramatically attenuates noise by 15–30 dB because water absorbs acoustic energy. Typical levels drop to 70–80 dB, often eliminating mandatory hearing protection and improving operator comfort. The deeper the water depth (e.g., 2–3 inches above the material), the greater the noise reduction, though excessive depth can affect cutting quality.

Dust and Mist Generation
Above-water cutting releases fine abrasive dust (silica, garnet) and metal particles into the air, creating respiratory hazards. Without an adequate mist collection system, airborne particulate levels can exceed OSHA limits, requiring expensive dust collection equipment and regular air monitoring. Underwater cutting traps nearly all airborne particles at the source. Dust and aerosolized metal are captured within the water bath, leaving clean air above the tank. This eliminates the need for mist collectors and reduces operator health risks. The only remaining concern is handling sludge during tank cleaning.

Operating Cost Comparison
Underwater cutting introduces additional costs: a deeper water table or submerged cutting tank requires more water volume, and water treatment or disposal costs may increase. The cutting head must be positioned farther from the material (standoff typically 5–10 mm vs. 3–5 mm above water), slightly reducing cutting speed (3–8% slower) due to jet energy loss passing through water. However, noise and dust reductions often allow shops to avoid purchasing or operating dust collection systems, which can cost 5,000–5,000–15,000 annually in energy and filter replacements.

Summary Table

Practical Recommendations
For materials generating hazardous dust (e.g., carbon fiber, lead, beryllium copper, or thick aluminum), underwater cutting is strongly preferred despite minor speed loss—savings from dust elimination often exceed lost productivity. For clean-cutting materials like stainless steel or plastic in a well-ventilated shop, above-water cutting may be more cost-effective, especially if noise is tolerable. Many modern waterjet systems offer adjustable water level to switch modes per job, providing flexibility. Ultimately, underwater cutting trades a small speed penalty for major health, safety, and dust control savings, making it the superior choice for most abrasive operations involving toxic or abrasive dusts.