Simulated effects of head movement on contact pressures between headforms and N95 filtering facepiece respirators part 2: simulation.

Finite element (FE) filtering facepiece respirators (FFRs) were developed and mated to the new headforms with a cervical spine model. The FFRs from three manufacturers included three sizing systems: (i) a single one-size-fits all, (ii) an FFR with two sizes (S/M and M/L), and (iii) an FFR with three sizes (S, L/M, XL). Finite element method (FEM) simulations of 16 headform and respirator combinations (5 headforms and 6 respirators) were used to examine maximum contact pressure changes for five cases: static head, flexion, extension, left rotation, and right rotation. For each of the 16 headform and respirator combinations, maximum contact pressures of the static headform and motile headforms were compared using t-tests. Significant differences on the maximum contact pressures were found in the extension, left rotation and right rotation at the nose (P < 0.005), the left rotation at the top of right cheek (P = 0.03), and the extension at the bottom of left/right cheek (P = 0.01). When separately considering each headform and each FFR manufacturer, the effects of the four head movement cases on the nose maximum contact pressure changes were observed in the simulations with all five headforms and all FFR manufacturers. The effects of the left and right rotations on the chin maximum contact pressure changes were observed in the simulations with the small headform. It was also found that the use of a nose clip could reduce the impact of the head left/right rotations on nose maximum contact pressure changes. In addition, head movements changed pressure contours of the key nose area. Caused by the head movements, the maximum contact pressure changes may affect seal quality, and the increase of the maximum contact pressures could reduce the facial comfort level.