When you cough or sneeze you tend to expel out respiratory waste which can be droplets larger than 5 micron or airborne droplet less than 5 micron both have different clinical implications. Droplets remain suspended in the air for a limited period only and exposure of less than 3 feet is usually required for human to human transmission of droplet borne respiratory organisms. In flu this can be up to 6 feet. The examples of droplet infections are meningitis influenza rubella German measles etc. No precaution needs to be taken by a person who is 6 10 feet away from the patient but if a person is sitting or working even 3 6 feet distance the non coughing person should wear a simple mask. Airborne droplet nuclei that carry respiratory secretion smaller than 5 micron can remain suspended in the air for extended period and can cause infections to people who are standing even more than 10 feet away. The example of airborne droplet nuclei infections are TB measles chickenpox and SARS. Patients with these diseases should be placed in an isolation room and all healthcare personnel who are looking after these patients must use a safe N95 mask. In normal house with windows opened there is a constant exchange of air which prevents spread of infections but in AC setups with no air exchange the infections can spread from one person to another. When sitting in an air conditioned atmosphere the setting of the AC should be such that the same air is not circulated and fresh air is allowed to exchange. Split ACs therefore are more dangerous than the window ACs. In an office with split AC if one employee is suffering from any of the droplet nuclei disease can transmit infection to others. Therefore patients with confirmed TV measles chickenpox and SARS should not be allowed to work in split AC atmosphere.