and creating local air movements, the ceiling fan operation reduced the exposed individual’s breathing zone concentrations by more than 20%. Airflow patterns generated from ceiling fans recirculates air vertically because ceiling fans generate inflow from overhead which creates an air distribution that is different from the typical wind which has horizontal flow directions. Ceiling fan airflow has a greater effect than supply air on aerosol transmission because the downward movement of the ceiling fan’s airflow can protect the underneath subject from exposure than when the subject was further from the fan. In a study comparing the airflow of ceiling fans to the supply air of diffusers, ceiling fans were proven to have a more significant effect on the droplet and airborne transmission, for it achieved a stronger protection for the subject under cough exposure. The research proved that ceiling fans showed strong potential to reduce the exposure risk to coughs that directed horizontally through the transient process. Safety concerns with installation A typical ceiling fan weighs between 8 and 50 pounds when fully assembled. While many junction boxes can support that weight while the fan is hanging still, a fan in operation exerts many additional stresses—notably torsion—on the object from which it is hung; this can cause an improper junction box to fail. For this reason, in the United States the National Electric Code (document NFPA 70, Article 314) states that ceiling fans must be supported by an electrical junction box listed for that use. It is a common mistake for homeowners to replace a light fixture with a ceiling fan without upgrading to a proper junction box. Low-hanging fans/danger to limbs Another concern with installing a ceiling fan relates to the height of the blades relative to the floor. Building codes throughout the United States prohibit residential ceiling fans from being mounted with the blades closer than seven feet from the floor; this sometimes proves, however, to not be high enough. If a ceiling fan is turned on and a person fully extends his or her arms into the air, as sometimes happens during normal tasks such as dressing, stretching or changing bedsheets, it is possible for the blades to strike their hands, potentially causing injury. Also, if one is carrying a long and awkward object, one end may inadvertently enter the path of rotation of a ceiling fan's blades, which can cause damage to the fan. Building codes