What would provide the best protection from large quantities of refrigerant leaking from a refrigeration unit in a semi-enclosed space?

Using a Self-Contained Breathing Apparatus (SCBA) offers the best protection in a scenario where large quantities of refrigerant are leaking into a semi-enclosed space. Refrigerants can displace oxygen and create an asphyxiation hazard, and certain refrigerants may also present toxicity risks. An SCBA provides a supply of clean, breathable air and protects the user from inhaling harmful gases or vapors during emergency situations.

While personal protective equipment and respirators may offer some level of protection, they do not guarantee a sufficient supply of breathable air in environments where the oxygen level may be dangerously low or when dealing with highly toxic substances. Ventilation systems can help mitigate the concentration of refrigerant in the air but might not be sufficient or available in emergency situations. Therefore, the self-contained nature of an SCBA ensures that the user has independent respiratory protection, making it the most effective choice in this context.