Evaluation of new in-facepiece sampling procedures for full and half facepieces.

Precision and bias were determined on five different methods of conducting in-facepiece sampling. In-board penetration occurred through fixed, circular, leak geometries positioned at different areas on the face-seal of full and half facepiece negative-pressure respirators. The sampling procedures evaluated in the study were: (1) a continuous, low sampling rate, flush on the respirator, mid nose-mouth probing (CLF) procedure; (2) a continuous, high sampling rate, deep front-of-mouth probing (CHD) procedure; (3) a pulsed exhalation, deep front-of-mouth probing (PED) procedure; (4) an exhalation value discharge (EVD) procedure; and (5) a pulsed inhalation, deep front-of-mouth, probing (PID) procedure. The CLF procedure represents a recommended in-facepiece sampling procedure in the United States. Evaluations were done on populations of nine full facepiece respirators and five half facepieces. The full facepieces were not equipped with nose cups. The average sampling biases on the full facepieces were: (1) CLF procedure, -21%; (2) CHD procedure, -3%; (3) PED procedure, 0.7%; (4) EVD procedure, -14%; and (5) PID procedure, -12.3%. On the five half facepiece respirators the average sampling biases were: (1) CLF procedure, -26%; (2) CHD procedure, -13%; (3) PED procedure, -4%; (4) EVD procedure, -2%; and (5) PID procedure, -24%. The bias observed with each method was found to be affected, to some extent, by the location of the face-seal penetration.