Used to test whether the wearer can detect the fit testing solution. Two avaliable as a small percentage of the population cannot detect sodium saccharin in which case the bitter soltuion should be used. (Or vice versa) For Occupational Use Only 3M™ recommends users are face-fit tested before using a respirator and repeated regularly as part of their occupational respiratory protection program Follow all applicable national and other guidance with respect to face fit testing. In the UK please see further guidance from the Health and Safety Executive (HSE) and their guidance document INDG 479