Which component is essential for ensuring the safety of CNG storage cylinders?

The essential component for ensuring the safety of CNG storage cylinders is a pressure relief system. This system is critical because it serves as a safety mechanism that prevents the pressure inside the cylinder from exceeding safe limits. In the event of an overpressure condition, the pressure relief system allows excess gas to escape, thereby preventing explosions or catastrophic failures that could occur due to excessive pressure buildup.

While other options such as a valve cap or guard, a corrosion-resistant coating, and an emergency shut-off valve also contribute to the overall safety of CNG systems, none of these are as crucial as the pressure relief system in directly addressing the inherent risks associated with high-pressure gas storage. The pressure relief system is designed specifically to manage the risks of pressure, making it the most essential component for safety in CNG storage cylinders.