Fifteen corn. filtering half masks were tested for protection efficiency against NaCl nanoaerosol (particle size range 10-250 nm, aerosol flow rate 45-255 L/min according to a std. method. The increase of the air flow rate resulted in an significant increase of nanoparticles penetration and the current requirements of filtration efficiency were exceeded several times. The valid stds. did not give any image of half mask efficiency against nanoparticles, because none of the current stds. covered the penetration of the particle size 20-50 nm.