When performing hydrostatic testing on piping, which safety principle is essential?

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Safety in hydrostatic testing relies on controlling energy and following recognized procedures. Using a proper test medium, typically water, provides a stable, incompressible medium that allows a controlled pressurization of the piping. Compressed air or other gases are dangerous because they store more energy and can cause violent releases if a leak or failure occurs. Before opening any fittings, depressurize and drain the system to avoid a sudden, high-velocity discharge. Maintain a safe distance and use barriers or exclusion zones to protect personnel from leaks or projectiles. Conduct the test per code or standard procedures, which specify the correct test pressure, duration, leak criteria, and proper shut-down and post-test steps. The other options ignore these critical safety practices and introduce unnecessary risk: testing with air, opening fittings under pressure, or disabling safety devices.