This report compares the fit test with PortaCount and particles with fit test using tear gas, regarding protection factors. Potential differences in protection factors between gas and particle challenge are examined and discussed. Protective factors obtained during the exposure to two different types of particles, combustion particles from tea light and generated salt particles, have been studied. After an assessment based on real exposure situations for the staff from the Swedish Customs, a fit factor of the respirator of at least about 10 000 is recommended. However, there may be other substances, that may require a higher fit factor, or even a self-contained breathing apparatus. Fit test with PortaCount is suitable for determining the required fit factors, and should essentially be used. To mimic a real exposure situation, and to provide greater confidence in the protection of the user, tear gas fitting should also be carried out to complement the PortaCount method. To obtain reliable fit factors with PortaCount, an active generation of the challenge aerosol should be used, eg via a salt aerosol generator. There are differences in the fit factors between gas and particles, and the relation between the differences is unclear.