In theory, using a high enough ventilation rate in a room can help reduce the concentrations of SHS produced from smoking. However, ventilation will not necessarily reduce levels of SHS to safe levels or eliminate SHS exposure. If one is in the same room as an active smoker, then during smoking one will be exposed to smoke that is being mixed in the room -- even if there is a high ventilation rate. Furthermore, if one is fairly close to the active smoker (within 3 to 6 feet), one's exposure is likely to exceed by several times that of a person positioned farther away from the smoker. This "proximity effect" will occur regardless of the amount of ventilation in the room.