time-period of days to a few weeks post-detonation which approximates the radioactive dose rate generated by the decay of the myriad of isotopes present in nuclear fallout, is the "7/10 rule". The rule states that for each 7-fold increase in time the dose rate drops by a factor of 10. For example, assuming the fallout process has ended 24 hours post detonation and the dose rate would be lethal if a few hours of exposure occurred, 50 roentgens per hour, then 7 days after detonation the dose rate will be 5 R/hr and 49 days after detonation (7×7 days) the dose rate will be 0.5 R/hr at which point no special precautions would need to be taken and venturing outside into that dose rate for an hour or two would pose a close to negligible health hazard, thus permitting an evacuation to be done with acceptable safety to a known contamination free zone. Following a surface-burst nuclear detonation, approximately 80 percent of the fallout would be deposited on the ground during the first 24 hours. Some agencies that promoted "evacuate immediately" guidance as a response to potentially lethal fallout arriving, advice which may have been influenced by these agencies assuming simplistic single wind-driven cigar/Gaussian shaped fallout contours would be representative of reality, have since retracted this advice. This can actually result in higher radiation exposures as it would put people outdoors and in harm's way when the radiation levels would be highest. The Modeling and Analysis Coordination Working Group (MACWG) – which was set up to resolve conflicting advice given by various agencies, has reaffirmed that the best blanket advice that would reduce the number of casualties by the greatest amount is: "Early, adequate sheltering followed by informed, delayed evacuation." Expert advice published in the 2010 document Planning Guidance for Response to a Nuclear Detonation is to shelter in place, in an area away from building fires, for at least 1 to 2 hours following a nuclear detonation and fallout arriving, and the greatest benefit, assuming personnel are in a building with a high protection factor, is sheltering for no less than 12 to 24 hours before evacuation. Therefore, sheltering for the first few hours can save lives. Indeed, death and injury from local fallout is regarded by experts as the most preventable of all the effects of a nuclear detonation, being simply dependent on if personnel know how to