Re-Usable 4000 Series Half Mask Respirators. These masks are available in two grades and are designed to give protection against fine dusts, oil, water based mists and organic vapours. Bonded carbon allows the gas/vapour filter to be moulded around the face to improve vision and balance. Textured face seal to provide a more comfortable fit. Parabolic exhalation valve gives easier breathing and reduces heat build up.The 4255 mask is approved to EN 405: 2002 FFA2P3D. Assigned protection factor for Gases & Vapours: 10 or 5000ppm which ever is the lower. Assigned protection factor for Particulates: 20.