Air traffic controllers in the US have been advised to take 26-minute naps  , after a series of accidents involving workers falling asleep. Now the National Transportation Safety Board (NTSB) is calling for "controlled naps" during nightshifts  . NTSB member Mark Rosekind said that a 26-minute nap would improve performance by 34%. He believes that beyond the aviation   industry, other professions, such as motoring and machinery, also carry obvious risks. But other experts doubt whether 26 minutes is the appropriate napping time. It's a bit too long and risks you falling into a deep sleep, says Jim Horne, director of the Sleep Research Council. He said, "A nap of about 15 minutes is best; once you get beyond 20 minutes, you risk a deep sleep and you can be much more tired when you wake up. Therefore, we suggest that a nap be combined with a cup of coffee so that you can enjoy an effective sleep before the caffeine   takes effect in 20 minutes. However, this method only works on those who have had a poor night's sleep. If you haven't had a sleep the night before, this method won't be enough to make you fresh."  Health writer, Linda Wasmer Andrews, also believes that 26 minutes is too long. She says a nap between 10 and 20 minutes is enough, and the timing of the nap is also important. Putting your head down too early means your body may not be ready to sleep yet, but a nap that is too late in a day might make it harder to fall asleep. Early afternoon is often the best time, between l pm to 3pm, when people experience a post-lunch decrease in energy. Jim Horne thinks that a 26-minute nap is not appropriate because   _  .
people risk a deep sleep and may feel more tired the guidelines for drivers can reduce the napping time people who had a poor sleep need some more napping time it's a little long for people who didn't sleep the night before