Health risks associated with the use of irritant smoke for qualitatively fit testing respirator facepieces were evaluated by NIOSH at the request of a municipal fire department. Fire fighters had been fit tested while wearing a self contained breathing apparatus in the pressure demand mode. Irritant smoke from air flow indicator tubes was puffed into a test hood over the head and facepiece. Four fire fighters experienced skin irritation or eye irritation after fit testing. The investigation involved particle size analysis of the smoke, and measurement of hydrogen-chloride (7647010) (HCl) levels produced by air flow indicator tubes. Particles were analyzed by laser aerosol spectrophotometry. HCl was measured using a portable air monitor. Results showed that HCl levels measured without the hood in place on a day with low (14%) relative humidity (RH) was less than 1 part per million (ppm), and on a day with high (53%) RH ranged from 100ppm at a distance of 6 inches from the tubing inlet to 11,900ppm at 2 inches. Six measurements at 12 inches did not detect HCl. The author concludes that the sampling results provide evidence that high concentrations of HCl are emitted from irritant smoke fumes in environments with low and high RH, and that exposure to the fumes should be considered a health risk. It is recommended that quantitative fit tests be conducted for facepieces as with other fire fighting equipment, but that they be done without the self contained breathing apparatus. Instead, full facepiece air purifying versions should be used.