9-1-1 are the numbers used in the United States if there is an emergency. Other countries have numbers to use in case of an emergency, but these numbers are only to be used if a person needs help. It is believed that this emergency number is always available, but there have been some cases where something occurs and causes the system to malfunction.
In one case, a storm came through Washington D.C. and this storm was so severe that it because the 911 system to fail. This is critical because people are counting on this system to send emergency personnel to the scene of an emergency. Verizon was responsible for failing the 911 system during this storm. However, after a small amount of time, they had it fixed.