One of the problems with many respiratory hazards (such as fumes or gases) is that employees cannot easily "see" them. Even more visible hazards, such as dusts, are often accepted as part of a "normal" work environment. As a result, many respiratory problems only become clearly evident well after the original exposure. Yet once they occur, most respiratory problems are "chronic" and long lasting. To further protect employees from these hazards, both OSHA and NIOSH have issued changes to their respiratory protection requirements.