Quarterly is the best answer because compressed air leaks reappear continuously as hoses, fittings, regulators, valves, quick connects, seals, and pipework degrade or are disturbed during normal operations. Annual testing is better than no program, but it allows energy waste to remain hidden for too long. Bi-annual testing is stronger, but quarterly inspection is the better reliability and energy-management practice for plants with significant compressed-air demand. Compressed air is expensive, and leaks create avoidable compressor load, wasted energy, reduced system pressure, poor tool performance, and additional equipment runtime. In CRL Asset Condition Management, compressed air leak detection is a condition-monitoring activity, commonly performed using ultrasound because leaks create high-frequency sound. The U.S. Department of Energy identifies ultrasonic acoustic detectors as an effective way to detect leaks, and current condition-monitoring guidance recommends quarterly or semi-annual ultrasonic surveys depending on plant size and usage. Given the answer choices, quarterly is the strongest best-practice frequency.