Emergency communication system
161 people were killed and at least 990 injured when an EF5 multiple-vortex tornado hit Joplin, Missouri. Because Joplin is located in a tornado-heavy area of the country, many people considered the tornado sirens routine and ignored them. Instead, many residents waited until they received confirmation from another, non-routine, source, such as seeing the tornado, a radio or TV report, or hearing a second siren. In the aftermath, an assessment team recommended that emergency warnings take risk perception into account to convey a sense of urgency. NOAA Officials are considering ways to change the warning system to distinguish smaller tornadoes from more deadly ones.
2011 Joplin tornado
In 2013, the American Society of Civil Engineers published a study disputing the tornado's initial EF5 rating, based on surveying damage on over 150 structures within a six mile segment of the storm's path. According to the report, over 83 percent of the damage was caused by wind speeds of 135 miles per hour or less, the maximum wind speed of an EF2 tornado. An additional 13 percent was caused by EF3 wind speeds, and 3 percent was consistent with EF4 winds. The study found no damage consistent with wind speeds over 200 miles per hour, the minimum threshold of an EF5 tornado. Researchers concluded that the inability to find EF5 damage was due to the absence of construction standards that were able to determine the necessary wind speeds. Bill Colbourne, a member of the engineering team that surveyed the damage, declared that "a relatively large number of buildings could have survived in Joplin if they had been built to sustain hurricane winds."