This has been an on-going argument for many years for the obvious reason that it costs employers serious time and money to comply with the regulation. This resistance has been so pervasive that some years ago a member of the US Congress passed a bill that prohibited OSHA from using any public funds to enforce the annual requirement. (This has since been overturned.)
We have seen numerous examples of respirators that do not fit the subject when they are fit-tested the following year. Primarily these are the N95-type filtering facepieces, but we have also observed the phenomenon with elastomeric respirators.
Because the pressure to change this requirement is so great, Dr. Ziqing Zhuang of NIOSH headed a study to develop actual statistics supporting the annual requirement.
View the CDC report of the study which contains the relevant literature citations.
Dr. Zhuang’s study makes the point that there is a significant chance of a fit having changed sufficiently in twelve months’ time- a chance large enough to warrant the annual requirement.
There is one other point to consider: the annual test allows a checkup of the wearer’s habits and procedures with regard to the actual use of the respirator.