Aworker who is not using fall arrest protection loses his footing at the top of a six-story building, calls for , and then falls. if his coworkers on the ground hear his cry, how much time do they have to take measures to break his fall

The correct answer is two seconds. 

This means that in the span of two seconds, someone can fall from the the top of a six-story building to the ground and very likely be seriously injured or killed. In such a short time span, it is highly unlikely that a fall can be broken and the person will be unharmed. Therefore, one must always ensure that he or she uses fall arrest protection when working at n elevation.