The QNFT is an assessment of the adequacy of respirator fit by numerically measuring the amount of leakage into a respirator.  A QNFT is required for all negative pressure full face and half face respirators that are to be used in atmospheres greater than 10 times the OSHA PEI. Our standards QNFT method uses ambient aerosol condensation nucli counter.  A Fit factor of >500 will be considered a pass for full face piece respirators unless you prefer a higher minimum number