OSHA 1910.134(f) states:
“The employer shall ensure that an employee using a tight-fitting facepiece respirator is fit tested prior to initial use of the respirator, whenever a different respirator facepiece (size, style, model or make) is used, and at least annually thereafter.” (Link: Read OSHA standards)
Employees issued powered air purifying respirators and supplied air respirators with loose-fitting facepieces, hoods or helmets are not subject to fit testing.
3M Personal Safety Division (PSD) offers a training video and other information on Respirator Fit Testing on its web pages. Some content is also available in Spanish.