Studies also found that worker-to-worker variation in the use of respirators can have very large effects on the protection achieved. A 1980 study on inhalation exposure of cadmium workers identified a single worker who always used his respirator correctly. The protection factor for this worker was found to be 26 times higher than that for the average worker. In a study in coal mines, miners frequently removed their respirators in conditions where they perceived the dust level to be low, greatly reducing efficacy. In another study, respirators with an expected protection factor of 1000 in fact had protection factors ranging from 15 to 216. Factors affecting the level of protection achieved include the snugness of the fit of the respirator to the worker's face, and air movement in the environment.
