[en] In August 1975, Lawrence Livermore Laboratory began to quantitatively fit all employees who are or may be required to wear any type of full-face respirator. After one year, 306 employees have been fitted. A total of 1362 tests were made, using seven makes of full-face respirators. Of the 306 employees fitted, 284 were tested using more than one make of full-face mask. All employees fitted could get a maximum use limit (MUL) of at least 100, 8 percent has a MUL of 100 to 499 on at least one of the makes of masks tested, 11 percent had an MUL of 500 to 999, 13 percent had an MUL of 1000 to 1999, 24 percent had an MUL of 2000 to 4999, and 44 percent had an MUL greater than 5000. These numbers were derived using the average of the peak leakages occurring during each of six exercises performed while wearing each mask. If the overall average leakage occurring during the six exercises rather than the peak average is used in the calculations, 90 percent of the employees could obtain an MUL over 1000 on at least one make of mask