Which method is not an example of large-scale sterilisation techniques?

Large-scale sterilization techniques are typically employed to ensure that medical and dental instruments and materials are free from microorganisms and are safe for use. Among the options provided, ultraviolet irradiation is not considered a large-scale sterilization technique.

Ultraviolet irradiation is primarily used for surface disinfection and is effective against a limited range of pathogens. Its mode of action involves damaging the DNA of microorganisms, which can be effective for smaller-scale applications, such as disinfecting surfaces and water. However, it lacks the penetration power required to sterilize products in bulk or within dense materials, making it unsuitable for large-scale sterilization processes.

In contrast, the other methods mentioned—'S'-type autoclave sterilization, ethylene gas exposure, and gamma irradiation—are designed for comprehensive sterilization of medical and dental tools. 'S'-type autoclaves use steam under pressure to achieve sterilization, effectively penetrating complex instruments. Ethylene gas is used for heat-sensitive items, providing effective sterilization without damaging the materials. Gamma irradiation utilizes high-energy radiation to destroy microorganisms on a large scale, allowing for the sterilization of various products, including pharmaceuticals and medical devices.

These distinctions highlight why ultraviolet irradiation does not fit into the category of large-scale sterilization techniques.