Final answer:
Respirators are the protective gear designed to supply fresh air to a welder, especially in hazardous environments. They can be equipped with their own air supply, distinct from welding helmets, face shields, and hard hats that do not have this feature.
Step-by-step explanation:
Among the options provided, respirators are the type of face and head protection that supply fresh air to a welder in a hazardous breathing environment. Respirators can be equipped with their own air supply to provide clean breathing air, which is essential when working in environments where air quality is compromised by gases, fumes, or particulates. Welding helmets, face shields, and hard hats offer protection against impacts, sparks, and intense light but do not typically supply fresh air.
For instance, the safety equipment used in BSL-4 laboratories includes suits with their own air supply. Similarly, in the context of firefighting, a lightweight breathing system including a face mask and air bottle has been developed, based on technology transferred from NASA's aerospace innovations. These examples illustrate how specialized respiratory protection is provided in environments where clean air is either not available or contaminated.