Tornado Disaster -- Texas, May 1997

On May 27, 1997, multiple tornadoes swept through Williamson and Travis counties in central Texas. The tornadoes caused 32 injuries, 29 deaths, and an estimated $20 million in personal and commercial insured losses. This report summarizes the injuries and deaths associated with these tornadoes based on information from emergency department and hospital records and death certificates.

Three tornadoes swept through the towns of Jarrell, Cedar Park, and Pedernales Valley at approximately 3:40 p.m., 4:00 p.m., and 4:50 p.m., respectively (Table_1). The first tornado, a slow-moving multivortex F-5 (Fujita Tornado Intensity Scale) (Table_2), swept a path 7.6 miles long and approximately 1320 yards wide through a residential subdivision of Jarrell, a predominantly rural town in Williamson County, destroying 30 permanent homes, eight mobile homes, and three businesses (Table_1). The second tornado (F-3) touched down in Cedar Park in Williamson County and swept a path 9.2 miles long and 250 yards wide, destroying 11 permanent homes and three businesses (Table_1). The third tornado (F-4) swept a path 5.6 miles long and 440 yards wide through Pedernales Valley, a heavily wooded area in western Travis County, destroying 15 permanent homes, three mobile homes, and two businesses (Table_1).

A total of 33 persons presented to six area hospitals for treatment of injuries sustained directly or indirectly by the three tornadoes. Of these 33 persons, 13 (39%) had multiple diagnoses. The categories of injuries included lacerations (18 {55%}), contusions (15 {46%}), abrasions (10 {30%}), strains/sprains/muscle spasms (six {18%}), fractures (two {6%}), penetrating wound (one {3%}), and closed-head injury (one {3%}). The median age of the injured persons was 38 years (range: 1-75 years). Twenty-seven persons were treated and released from area hospitals, and five were admitted; one person died in an emergency department. Among patients admitted to the hospital, the median length of stay was 21 days (range: 1-31 days). Four persons were discharged, and one person was transferred to an inpatient rehabilitation facility.

Of the 29 tornado-related deaths, 27 (93%) occurred in Jarrell. Decedents' ages ranged from 5 to 69 years (median: 22 years), and 14 (48%) were aged less than 18 years; most (16 {55%}) were males. All but one death occurred at the site of the tornado. The immediate cause of death for 26 (90%) of the victims was multiple traumatic injuries; other causes of death included myocardial infarction, head injury, and asphyxia. At the time the tornadoes struck, none of the decedents were in structures with basements. In nine families, there were two or more deaths, and five members of one family were killed.

Tornado watches were issued by the National Weather Service (NWS) for Williamson County at 12:54 p.m. and Travis County at 3:31 p.m. Tornado warnings were issued for Williamson County at 3:30 p.m. and Travis County at 4:09 p.m. (Table_1). None of the three areas had tornado shelters or warning sirens. The Jarrell volunteer fire department siren was sounded when the tornado was spotted; however, this siren is not used as a tornado warning but to summon volunteers to the firehouse. Jarrell had experienced an F-3 tornado in 1989, resulting in one death and 28 injuries. Tornadoes have not been reported previously in Cedar Park or Pedernales Valley.

Reported by: Williamson County Emergency Medical Svcs; J Hobbs, J Bitts, Williamson County Justices of the Peace, Williamson County; R Bayardo, MD, Travis County Medical Examiner; Travis County Emergency Medical Svcs, Travis County; Div of Emergency Management, Texas Dept of Public Safety; Bur of Vital Statistics; D Zane, D Perrotta, D Simpson, MD, State Epidemiologist, Texas Dept of Health. J Henderson, A Dreumont, L Eblen, National Weather Svc. American Red Cross. Environmental Hazards Epidemiology Section, Health Studies Br, Div of Environmental Hazards and Health Effects, National Center for Environmental Health; Div of Applied Public Health Training (proposed), Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: During 1953-1991, the number of tornadoes and tornado-related deaths were greater in Texas than in any other state (2,3). However, by state-specific areas, Texas ranks ninth and Florida ranks first in number of tornadoes per 100,000 square miles (2). The Fujita Tornado Intensity Scale (F-0 through F-5) ranks tornadoes according to their estimated speed, damage to structures, and damage to the environment (Table_2) (1). Most tornadoes (60%) are weak (F-0 or F-1) and have limited injury or destruction potential (2). Although violent tornadoes (F-4 and F-5) are rare (1%-2%), they cause severe damage and account for approximately half of tornado-related deaths (2). During 1990-1996, only five tornadoes in the United States were assigned an F-5 rating (NWS, unpublished data, 1997). Previous F-5 tornadoes in Texas occurred in 1976 in Brown County and in 1973 in McLennan and Bosque counties (2); although no injuries or deaths were associated with either tornado in 1973, 11 nonfatal injuries were reported in the 1976 tornado (2). The last F-5 tornado in Texas involving deaths occurred in Lubbock in 1970 and accounted for 28 deaths and 500 injuries (2,4).

The risk for injury and death increases with a tornado's intensity (3). Factors associated with fatalities in Jarrell may have included the intensity and slow progression of the tornado and the lack of underground shelters, such as basements. In many southern states, including Texas, homes are often constructed on concrete slabs; approximately 20% have partial or full basements (5). NWS interviews with area residents after the tornadoes in 1997 indicated that most persons in the paths of the storms understood tornado safety and followed recommended protocols for homes without basements by seeking shelter in hallways or interior rooms (J.H. Henderson, NWS, personal communication, 1997). Survivors in the path of the Jarrell tornado were in bathrooms or in a storm cellar built by a neighbor. Survivors of the Cedar Park and Pedernales Valley tornadoes sought shelter in interior rooms or bathtubs.

NWS tornado watches and warnings are the primary method of alerting communities of an approaching tornado and are disseminated through public safety organizations, sirens, television, radio, or other electronic media (6). A tornado watch is issued when weather conditions indicate that a tornado may develop; a tornado warning is issued when a tornado has been sighted or detected by advanced weather technology (6). Weather warnings can be received directly from the NWS through the National Oceanic and Atmospheric Administration (NOAA) weather radio network. Weather radios are equipped with a battery back-up and stand-by feature that emits a high-pitched tone followed by an official NWS report. This type of radio is activated for all NWS severe weather warnings in an approximate 40-mile radius (6). Recent technology changes in the NOAA weather radio network includes a Specific Area Message Encoder (SAME) (7) that allows the NWS to alert specific counties within the 40-mile radius when severe weather is expected or ongoing. SAME will reduce the number of counties alarmed by the older weather radios for severe weather in adjacent counties. Both types of weather radios are commercially available.

Persons who attempt to outrun tornadoes in vehicles are at high risk for injury or death (8,9); when possible, those in high-risk areas should seek adequate shelter, preferably below ground. NWS offers the following recommendations for persons in areas for which tornado warnings are issued: 1) abandon vehicles and take shelter in a permanent structure or lie flat in nearby ditches or depressions; 2) in permanent homes or buildings, move to predesignated shelters, such as basements, and stay away from windows; 3) if underground shelters are unavailable, move to interior rooms or hallways on the lowest floor and get under a piece of sturdy furniture; 4) abandon mobile homes and take shelter in a permanent structure; and 5) if outside, lie flat in nearby ditches or depressions (6).

References

1. National Weather Service. Advanced spotters' field guide. Silver Spring, Maryland: US Department of Commerce, National Oceanic and Atmospheric Administration, 1993.

2. Grazulis TP. Significant tornadoes 1680-1991. St. Johnsbury, Virginia: Environmental Films, 1993.

3. Lillibridge SR. Tornadoes. In: Noji EK, ed. The public health consequences of disasters. New York: Oxford University Press, 1997.

4. Environmental Sciences Services Administration. The Lubbock, Texas tornado: a report to the administrator. Rockville, Maryland: US Department of Commerce, 1970; Natural Disaster Survey report no. 70-1.

5. US Department of Commerce/US Department of Housing and Urban Development. The American Housing Survey for the United States in 1995. Washington, DC: US Department of Commerce, Economics and Statistics Administration, Bureau of the Census/US Department of Housing and Urban Development, Office of Policy Development and Research, 1997. (Current housing reports H150/95RV).

6. National Weather Service. Tornadoes...nature's most violent storms: a preparedness guide. Silver Spring, Maryland: US Department of Commerce, National Oceanic and Atmospheric Administration, September 1992; publication no. 92052.

7. National Weather Service. Weather service operations manual: regional operations manual update. Silver Spring, Maryland: US Department of Commerce, National Oceanic and Atmospheric Administration, June 1997.

8. Glass RI, Craven RB, Bergman DJ, et al. Injuries from the Wichita Falls tornado: implications for prevention. Science 1980;207:734-8.

9. National Oceanic and Atmospheric Administration. The Red River Valley tornadoes of April 10, 1979: a report to the Administrator. Rockville, Maryland: US Department of Commerce, 1980; Natural Disaster Survey report no. 80-1.

TABLE 1. Population of towns struck by tornadoes and characteristics of
injuries, deaths, damage, and each tornado, by location -- Williamson and
Travis counties, Texas, May 27, 1997
===============================================================================
                                              Town
                             --------------------------------------------------
Population/Characteristics     Jarrell*   Cedar Park*   Pedernales Valley+
-------------------------------------------------------------------------------
Estimated population              800        15,000            7,000
Persons injured
Level of care
  Treated and released              8          14                5
  Hospitalized                      4           1                0
  Total                            12          15                5
Median age (yrs)                   25          45               47
Deaths
Cause
  Multiple trauma                  26           0                0
  Myocardial infarction             0           1                0
  Asphyxia                          1           0                0
  Head injury                       0           0                1
  Total                            27           1                1
Median age of decedents (yrs)      17          69               25
Buildings destroyed
Permanent homes                    30          11               15
Mobile homes                        8           0                3
Businesses                          3           3                2
Tornado characteristics
Watch issued                   12:54 pm     12:54 pm          3:31 pm
Warning issued                  3:30 pm      3:30 pm          4:09 pm
Time of impact                  3:40 pm      4:00 pm          4:50 pm
Intensity                         F-5         F-3               F-4
-------------------------------------------------------------------------------
* Williamson County.
+ Travis County.
===============================================================================

TABLE 2. Fujita Tornado Intensity Scale *
============================================================================================================
Category   Description             Approximate wind speed  Examples of damage
------------------------------------------------------------------------------------------------------------
F-0        Gale tornado             40- 72 mph             Chimney damage; broken tree limbs; small
                                                           trees uprooted

F-1        Moderate tornado         73-112 mph             Roof surfaces partially removed; mobile
                                                           homes overturned; moving automobiles pushed
                                                           from roads

F-2        Significant tornado     113-157 mph             Roof surfaces removed; mobile homes
                                                           demolished; railroad cars overtuned; large
                                                           trees uprooted or split; lightweight objects
                                                           thrown

F-3        Severe tornado          158-206 mph             Roofs and walls removed; trains overturned;
                                                           most trees uprooted; heavy cars thrown

F-4        Devastating tornado     207-260 mph             Houses leveled; structures with foundations
                                                           moved; heavy cars and large objects thrown

F-5        Incredible tornado      261-318 mph             Homes destroyed; trees debarked; cars thrown
                                                           100 yards; incredible phenomena occur
------------------------------------------------------------------------------------------------------------
* Reference 1
============================================================================================================

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