Which of the following is NOT one of the four cylinder safety systems?

The correct choice identifies a system that is not recognized among the established cylinder safety systems. The four main safety systems for gas cylinders are designed to ensure proper connection and prevent the misuse of gases.

The ASSS, which stands for American Standard Safety System, is used primarily for high-pressure cylinders and varies with the diameter and threading of the outlet. The PISS, or Pin-Indexed Safety System, is utilized for smaller gas cylinders to prevent the incorrect connection of different gases through the use of pins in the cylinder valve. The DISS, which stands for Diameter-Indexed Safety System, is designed for low-pressure connections and also prevents the incorrect linkage of gas delivery systems.

C. FISS, however, is not an established system used in the safety of gas cylinders. This makes it the correct answer as it does not belong to the recognized safety systems like the others do. Understanding these systems is crucial for maintaining safety standards and ensuring that medical gases are handled properly.