A revision of NIOSH’s method for analysis of asbestos and other fibers by phase-contrast microscopy (PCM) has been added to the NIOSH Manual of Analytical Methods. Dated June 14, 2019, the revised method presents alternative procedures for preparing and mounting asbestos samples on microscope slides for counting fibers under PCM, a technique that renders visible the changes in light waves as they pass through objects. The revised method also explains the optional but recommended use of special slide coverslips intended to improve laboratory microscopists’ accuracy when counting fibers.  The rules governing which entities seen through the microscope should count as asbestos fibers remain unchanged.  Martin Harper, who coauthored the revised method, emphasized that the changes give laboratories the flexibility to choose among combinations of treatments and mounting media. “There’s been no major change [in the revised method] that would cause folks to have to rush out and make substantial changes to what they’re doing,” Harper said. “There are now choices and clarifications in the method that are intended to be helpful to people and to allow them the leeway to do some things a little differently.” The revised method allows laboratories to use a dimethylformamide solution and a resin called Euparal instead of acetone and triacetin resin to mount sample material on slides. Because Euparal and triacetin have almost identical refractive indexes, Harper explained, the use of one or the other will not alter what analysts see through PCM. The disadvantage of triacetin is that too much of it can cause the fibers on a slide to move, Harper said. Fixing the fibers in place is easier to achieve with Euparal. Keeping the fibers from moving is necessary for analysts who follow the revised method’s instructions for using slide coverslips with relocatable fields. These coverslips are printed with a numbered and lettered grid that allows analysts to repeatedly return to the same field.