It is hazardous to look at the Sun at any time without suitable eye protection. Because the Sun is intensely bright, looking at the Sun will cause irreparable damage by burning the retina. Humans have a natural response to look away when attempting to look at the Sun. When there is an eclipse and particularly when the Sun is reduced to a thin crescent, the "look away" response diminishes and people, especially young children are tempted to look. If you can see any part of the Sun's surface it will still cause eye damage.
Only when the Sun's surface is completely covered during the total phase of a total solar eclipse is it safe to look at the eclipse without eye protection. Safe solar filters can be used to view the partial phases providing they have been manufactured especially for that purpose and have been appropriately certified. It is NOT SAFE to use anything else, including stacked sunglasses, exposed film or other similar items.