Doing sports high in the mountains is dangerous in itself. And when the overcrowding of the past years is added in, great problems can occur. Climbers have to wait their turn in certain areas which can cause their falling in domino fashion or movement of the surface due to excess weight. However, although the number of climbers of Mount Everest has recently grown exponentially, the ratio of accidents has lowered. It is the Himalayan peak with the least number of accidents proportionally.
Making a great physical effort under atmospheric pressure and without oxygen can cause important physical difficulties. And also, people going to Nepal have to have several vaccinations.
Most of those who reach the summit do so between 5 A.M. and 10 A.M., since beginning the descent later than that ca be very dangerous.