Does That Face Mask Really Protect You?

Abstract

Various types of face masks available to the general public are worn for protection against inhalation of dust, pollutants, allergens, and pathogenic organisms. Recent news stories have illustrated the widespread use of face masks for protection against Swine flu (H1N1), Severe Acute Respiratory Distress Syndrome (SARS), Highly Pathogenic Avian Influenza (HPAI) virus outbreaks in Asia, and dust from the collapse of the World Trade Center. However, the level of protection provided by face masks is unknown. The objective of this study was to determine how efficiently face masks prevent respiratory exposure to potentially harmful aerosols. Three types of commonly available face masks were tested: a surgical mask, a pre-shaped dust mask, and a bandana. An N95 respirator was tested as the positive control. Masks were fit onto a Styrofoam™ mannequin head modified with a 5/8-inch diameter sample probe that was placed inside a 147.5 liter test plenum; a 5/8-inch diameter reference probe was positioned next to the mannequin head. Saline aerosols were generated in the test plenum using an IV HEART™ (Westmed, Inc., Tucson, AZ) nebulizer. Each face mask was challenged for 30 minutes. Filter samples were collected simultaneously from the mannequin and reference sample probes and used to calculate aerosol concentrations. The mannequin sample probe and the reference sample probe volumetric flow rates were 8.75 L/min and 1.72 L/min, respectively. The mean challenge aerosol concentration, determined from the reference sample probe, was 0.045 ± 0.008 mg/L with a mass median aerodynamic particle size of 1.6 μm. Face mask protective efficiency was calculated as the ratio of mannequin sample probe concentration to reference sample probe concentration. The protective efficiencies were 33.3%, 11.3%, and 6.1% for the surgical, bandana, and dust masks, respectively. The N95 mask protective efficiency was 89.6%. In conclusion, the surgical mask protected the best of the three face masks tested. However, it is important to note that all three masks offer very little protection when compared to the N95, and wearing these face masks may produce a false sense of protection.