This is a report I wrote a couple of years ago which I rediscovered the other day.
Introduction
Since the Wichita Falls Tornado (1979) in Texas resulted in a number of vehicle-related fatalities, emergency management organizations have frequently recommended that the occupants of a vehicle that is threatened by a tornado should abandon their vehicle. They are often instructed, if no sturdy shelter is available, to lie down in a low-lying area, rather than remaining inside the vehicle. Recent studies (e.g. Schmidlin et al., 2008) have called these recommendations into question. Safety recommendations in the United States have recently been modified to adopt the results of these studies.
Canada experiences a high rate of tornadic activity and is second only to the United States in tornado frequency. In particular, the province of Ontario experiences the highest frequency of tornadoes within Canada. As of the time of publication, the tornado safety recommendations for Ontario, Canada have not been changed to incorporate the results of these studies
Objective
The objective of this paper is to provide insight into whether sheltering in vehicles or using a vehicle to travel to shelter is a recommendation that emergency managers should support. This report will examine the two aspects of this debate: 1) the use of a vehicle to drive to secure, sturdy shelter; 2) the use of a stationary vehicle as a form of shelter during a tornado.
Tornado Safety Recommendations
The origin of the recommendation to avoid vehicles during a tornado is often attributed to the Wichita Falls Tornado. The Wichita Falls Tornado was one of ‘The Red River Valley Tornadoes’ of April 10th, 1979. On this date, three very large tornadoes, each with durations of an hour or more and damage paths that were wider than average; moved across the Red River Valley area. They left in their wake a continuous swath of damage 35 miles or longer, many fatalities and hundreds of injuries.
This storm had a long warning lead time. At the time that the tornado struck Wichita Falls, severe weather warnings had already been in effect for nearly an hour. In Wichita Falls, tornado warnings were repeatedly broadcast by two local television stations and three local radio stations. Watch and warning information was continuously updated and well disseminated through direct telephone calls from National Weather Service Forecasters to local media outlets. In addition to the warning information that was being broadcast, the city also activated its siren system.
While many people sought shelter in their immediate area, others chose to flee from the approaching tornado in vehicles. The tornado caused 42 fatalities in Wichita Falls, of which 25 fatalities were vehicle related. Of the 25 vehicle related fatalities, 16 had gotten into their vehicles with the sole intention of avoiding the tornado. There can be little doubt that these 16 people would have fared significantly better since 11 of their houses suffered no damage from the tornado (Burgess, 2010).
In the United States, revised tornado safety recommendations have been referred to as forcing ‘a paradigm shift from the suggestion to abandon one’s vehicle, to encouraging motorists to remain inside one’s vehicle’ (Blair and Lunde, 2010). The revised safety recommendations from the American Red Cross in regards to vehicles for example, now state
• If you have access to a sturdy shelter or a vehicle, abandon your mobile home immediately.
• Go to the nearest sturdy building or shelter immediately, using your seat belt if driving.
If you cannot quickly walk to a shelter:
• Immediately get into a vehicle, buckle your seat belt and try to drive to the closest sturdy shelter.
• If flying debris occurs while you are driving, pull over and park.
Now you have the following options as a last resort:
• Stay in the car with the seat belt on. Put your head down below the windows, covering with your hands and a blanket if possible.
• If you can safely get noticeably lower than the level of the roadway, exit your car and lie
in that area, covering your head with your hands.
• Your choice should be driven by your specific circumstances.’ (American Red Cross, 2009).
This shift in thinking occurred due to the results of several scientific studies on the degree of vehicle damage caused by tornadoes. Several studies have argued that the recommendation to lie down in a ditch or other low-lying area if no sturdy shelter is available rather than seeking shelter in a vehicle is not supported by research (Schmidlin and King; 1996; Hammer, Ono and Schmidlin, 1999). Other studies have questioned whether sheltering in a low-lying area outdoors rather than sheltering in a vehicle is a safer option (Carter at al. 1989; Duclos and Ing 1989).
It is important to note that two forms of sheltering using a vehicle are mentioned. The first is using the vehicle to drive to secure, sturdy shelter. The second is to use a stationary vehicle as a source of shelter during the tornado.
Tornadoes in Ontario
Southern Ontario experiences the greatest number of tornadoes in all of Canada (Etkin et al., 2001), although tornadoes have been reported even in the northern parts of the province. Southern Ontario also has the highest population density and the greatest amount of critical infrastructure in Ontario which increases the risk of casualties and property damage.
According to Environment Canada, Ontario has an average of eleven tornadoes per year. However, this number may be higher as some tornadoes cause no damage to property (and are therefore not confirmed and/or rated), occur in unpopulated areas or simply go unreported.
Tornadoes can occur at any time of the year and at any time of day. They are most common in Ontario from May to September, with a peak in occurrence in June and early July (Etkin et al., 2001).The majority of tornadoes occur in the afternoon and early evening.
The vast majority of tornadoes in Ontario are weak (ranking as F0 or F1 on the Fujita scale for tornado intensity). There have been no reported F5 tornadoes (the highest ranking on the Fujita scale) in Ontario. However, there is no evidence that suggests that an F5 cannot occur in Ontario. Ontario is also not immune to tornado outbreaks, in which multiple tornadoes are reported.
Figure 1. The total tornado occurrence in Ontario (1979 – 2004) (Environment Canada, 2010).
As of January, 2011, Environment Canada and the Canadian Red Cross still recommend that people who are outdoors when a tornado threatens and have no sturdy shelter is available nearby, should take shelter by lying down in a ditch or other low-lying area. The Canadian Red Cross specifically addresses vehicles in their safety recommendations by saying ‘If you are in a car or mobile home, get out immediately and head for safety. You’ll want to get out of your car because it could be blown through the air or roll over on you.’ (Canadian Red Cross, 2001).
Use of a Vehicle to Seek Shelter
A study by Hammer and Schmidlin (2002) surveyed residents of suburban Oklahoma City after the tornado outbreak on May 3rd, 1999. This outbreak produced more than 70 tornadoes across Oklahoma and Kansas and resulted in 48 fatalities (NWS, 1999). The Oklahoma City Tornado (F5) was the deadliest tornado in the outbreak and was noted as being unusual for its long path, intensity and the long warning lead times. The residents who participated in this study were at home when the tornado warnings were issued and had their houses destroyed by the tornado. This study examined the outcome of people who used their vehicles to remove themselves from the path of the tornado or to seek a safer shelter. The results found that 47% of those surveyed left their houses and that 53% of those who left used a vehicle. While the majority of those who left their houses did so to go to a storm shelter (65%), others used their vehicles to get out of the path of the tornado. The study found that none of the people who used a vehicle to either get to a storm shelter or to drive out of the path were injured, whereas 30% of the people who stayed inside their houses were injured.
Use of a Vehicle as a Form of Shelter
The susceptibility of mobile homes to tornadoes has been well document (e.g. Chaney and Weaver, 2002). Schmidlin and King (1995) suggested that residents of mobile homes that do not have any sturdy shelters nearby may be safer if they took shelter in their vehicles than remaining in the mobile home or lying down in a low-lying area outdoors. This suggestion stemmed from their observations that at sites in which mobile homes had been destroyed and the occupants killed by a tornado that their vehicles appeared to have sustained little damage and often remained upright.
In 1999, King et al. surveyed the condition of a total of 70 vehicles that were parked outdoors within 10 meters of a house that had experienced tornado damage ranging from F1 – F4. Prior research by Schmidlin et al. 1998 had found no significant statistical difference in the percentage of cars tipped over, moved more than a meter or that would have had seriously injured occupants (had the vehicles been occupied at the time that the damage occurred) between F1 and F2 levels of damage and between F3 and F4 levels of damage. Differences in the impacts to the vehicle and its potential occupants only became statistically significant between F2 and F3 levels of damage. The authors suggest that the results indicate that vehicles are able to withstand the wind speeds of F1 and F2 tornadoes that would result in the destruction of mobile homes.
A study by Blair and Lunde (2010) examined the impacts of tornadoes on vehicles that were struck on Interstates. Occupants of vehicles driving on Interstates and other long, possibly remote stretches of road may experience situations similar to that of mobile home residents during a tornado in which there is no sturdy shelter nearby. In situations such as these, the only options may be to lie down in a low-lying area or to remain inside the vehicle.
A total of 263 vehicles were impacted by tornadoes with varying degrees of damage during the course of the study. Some of the types of damage noted by Blair and Lunde (2010) include broken windows, body damage, vehicles moved or blown off the road, or a vehicle rolled, overturned, tossed, or otherwise destroyed.
Figure 2. Damage to a vehicle (which was reported as being almost new) from an EF4 tornado near Little Rock, Iowa. (NWS, 2010).
This study found evidence that vehicles do not suffer significant damage from EF0 tornadoes. Tornadoes with a rating of EF0 account for approximately 62% of all tornadoes in the United States. During the course of this study, only 14.1% of the vehicles impacted by tornadoes which were surveyed had been damaged by an EF0 tornado. This suggests that vehicles are relatively undamaged by tornadoes with estimated wind speeds of less than 86 mph.
The study by Blair and Lunde (2010) included seven tornadic events that results in eight fatalities. All of the tornadoes that result in fatalities in this study were EF3 or greater in intensity. However, it is difficult to draw any conclusions from this due to the low number of events that resulted in fatalities and significant unknown factors such as whether the people who were killed had stayed in their vehicles or sought shelter outside in a low-lying area.
Tornado Fatalities by Location
Information on the number of tornado fatalities by location was obtained from the National Ocean and Atmospheric Administration for the United States since no information was available for Canada at the time this report was written, and is displayed in the figure below.
Figure 3. The percentages of the total number of tornado-related fatalities from 1985 – 2003 in the United States (SPC, 2010).
The information displayed in the figure does not suggest that people who remain in houses during a tornado are more likely to perish rather than those who are in vehicles, just as it does not display the inherent risk of each form of shelter; it only acts as a proxy for the number of people that are in that particular type of shelter when a tornado strikes. Safety recommendations since the Wichita Falls Tornado in 1979 have strongly emphasized seeking shelter in a sturdy building rather than taking shelter in a vehicle. The greater number of fatalities in houses may be attributed to a large number of people heeding the safety recommendation, resulting in a greater number of people staying in their homes and minimizing the number of people in forms of shelter. The probability that fatalities will occur in vehicles decreases if fewer people are in vehicles when the tornado strikes.
Discussion
The degree of risk given for different shelter types, including vehicles, in a tornado is unknown and is dependent on a number of uncontrolled variables that can differ greatly depending on the circumstances of each event. The Wichita Falls Tornado of 1979 occurred in conjunction with factors that made attempting to escape from the storm in vehicles a poor choice that resulted in many injuries. The Oklahoma City Tornado of 1999 occurred in conjunction with a number of factors that resulted in the choice of escaping in vehicles being beneficial.
Whether the public response to Oklahoma City Tornado in 1999 and its outcomes are the exception rather than the rule is unknown. The public and the media in Oklahoma have a high degree of awareness of tornadoes due to the high frequency in which they occur within that particular state. The tornado also occurred during daylight hours and had a highly visible funnel that could easily be identified as a tornado (NWS, 1999). In addition, it occurred in an area with a high number of storm spotters who could report its movement and broadcasts were able to use real-time, street-level mapping of the path which kept the public informed on the specific whereabouts of the tornado. These factors, combined with the long lead warning times and the advice of a local meteorologist to seek shelter underground or get out of the path of the storm, were found to have played an important role in the residents’ decisions to stay or leave their houses.
Not all tornadoes are as easily identifiable as the Oklahoma City Tornado. Many tornadoes are obscured by rain or hail, occur during night, or do not display the expected ‘funnel’ shape that the public has associated with tornadoes. In addition, the topography and the built environment of an area may restrict the visibility of the tornado. Real-time, street-level mapping of tornado paths is becoming more common in the United States, however, that technology is not yet readily available within Canada. Without this type of mapping (or other similar methods) the relatively immediate location of the tornado is unknown and a much broader area is identified as being at risk. This could lead to significantly greater numbers of people being encouraged to leave their homes in Ontario.
A significant role of the emergency manager is to develop and maintain measures that will assist in preventing, preparing, mitigating, responding and recovering from emergencies. Safety recommendations are often developed to incorporate advice that will assist the public in surviving particularly severe events. The wide audience, the variability in the warning lead time and the need to ensure that key messages are transferred to the public results in these often being brief and general statements, which may not be applicable to every tornado and every individual’s specific situation.
While studies have suggested that vehicles may be subjected to EF0 tornadoes and emerge generally undamaged (Blair and Lunde, 2010), the recommendation that people take shelter in their vehicles is likely to be poor advice in situations with a stronger tornado. Whether sheltering in a vehicle is inherently less of a risk than sheltering in a low-lying area outdoors is unknown. There are several dangers associated with sheltering outdoors in a low-lying area. Low-lying areas such as ditches are prone to flooding. It has also been reported that debris from tornadoes and high winds tends to accumulate in low-lying areas. This could result in a person surviving a weak tornado only to be trapped by debris and subsquently drowned. This situation may result in a vehicle being a slightly less risky choice than a low-lying area for surviving a weak tornado. However, it should be noted that in most cases the tornado intensity is determined after the tornado has occurred. The general public is unlikely to have the experience, the time, or the ability to see debris, to estimate the intensity of an approaching tornado. Either way, retreating to an underground shelter or a well-built house or building is associated with much less risk than other forms of shelter (Brenner and Noji, 1995).
The use of vehicles to remove their occupants from the path of a tornado may also be a reasonable choice in some situations in which there may be a long warning lead time and the path of the tornado is well disseminated. However, emergency managers must consider secondary hazards which may also endanger human safety. If safety recommendations begin to recommend that people drive to safety, it is possible that the number of people who heed this advice could be large enough to result in traffic delays and accidents which could result in people being trapped in their vehicles as the tornado approaches. Even the caveat that only those with no secure shelter in their immediate vicinity may still result in traffic hazards depending on the number and the condition of roads and leading away from the tornado.
In 1999, additional field work was undertaken after the May 3rd, 1999 tornado outbreak. The results from the King et al. survey and the additional field work by Ono (2002) are displayed in Table 1.
Table 1. The percentage of vehicles surveyed in the King et al. study (2002) and the Ono fieldwork (2002) that experienced different types of damage.
| King et. al study |
F1/F2 Damage |
F3/F4 Damage |
| Vehicles Not Tipped Over |
96% |
82% |
| Vehicles Not Moved (> 1m) |
70% |
50% |
| Would Not Have Seriously Injured Occupants |
84% |
64% |
| Ono Field Work |
F1/F2 Damage |
F3/F4 Damage |
| Vehicles Not Tipped Over |
n/a |
36% |
| Vehicles Not Moved (> 1m) |
n/a |
10% |
| Would Not Have Seriously Injured Occupants |
n/a |
32% |
The additional fieldwork done by Ono (2002) found fewer vehicles that had not been tipped over, moved more than a meter or that sustained damage that could have resulted in seriously injured potential occupants. The reasons for the greater amount of damage to the vehicles is unknown, however, the authors do offer several possible explanations. The Fujita Scale uses a range of wind speeds for each category. It is possible that the tornado responsible for the damage surveyed by Ono had wind speeds on the higher end of F4 category than the other F4s that were previously surveyed. Since damage is generally a function of wind speed, the higher the winds that an F4 tornado has, the greater the potential damage. However, in order to substantiate this claim, it would be necessary to assess the differences in damage caused by differing wind speeds within the F4 range.
The field work done by King et al. (2002) and Ono (2002) shows the potential variability of the degree of protection offered by vehicles. Many variables can influence the amount of damage suffered by a vehicle and its occupants including the path and intensity of a tornado and the amount and composition of airborne debris. In addition, the protection offered by a vehicle over that of a low-lying area depends on variables such as the presence of secondary hazards such as flooding or hail, exposure and once again, the amount and composition of airborne debris which could fall into the low-lying area, harming the person. Variables which affect the likelihood of escaping a tornado in a vehicle include traffic and road conditions, visibility, damage (e.g. fallen trees), lead warning time and topography. All of these variables can differ, not only for each tornado, but also for each individual’s situation.
Conclusion With so much variability that can greatly influence the likelihood of an individual’s ability to survive a tornado, emergency managers should continue to focus on encouraging people to take shelter in a location that is known to increase the odds of surviving a tornado, such as a tornado shelter or a basement (Doswell, and Brooks, 2002), rather than encouraging people to shelter in vehicles. It should be stressed to the public that the degree of protection offered by vehicles can vary greatly depending on each situation and that vehicles should still be a last resort when a tornado threatens.
In order to decrease the number of people whose only choices left are a vehicle or a low-lying area, emergency managers should strongly encourage people to take protective actions immediately once a warning is issued, rather than waiting until only poor shelter choices, such as vehicles are the only options available.
References
American Red Cross (2009). What Should I Do If A Tornado Is Threatening? Preparedness Fast Facts. http://www.redcross.org
Blair, S.F. and Lunde, E.P.K. (2010). Tornadoes Impacting Interstates: Service and Societal Concerns. Severe Storms Meteorology. Vol.5, No.4. pp.50 – 69.
Burgess, D. (2010). The April 10, 1979 Severe Weather Outbreak. http://www.srh.noaa.gov/oun/?n=events-19790410-burgess
Canadian Red Cross (2001). Are You Ready For A Tornado? Tornado Safety. http://www.redcross.ca
Chaney, P.L. and Weaver, G.S. (2010). The Vulnerability of Mobile Home Residents in Tornado Disasters: The 2008 Super Tuesday Tornado in Macon County, Tennessee. Weather, Climate and Society. Vol. 2, Iss.3, pp. 190 -199.
Doswell, C.A. and Brooks, H.E. (2002). Lessons Learned from the Damage Produced by the Tornadoes of 3 May 1999. Weather and Forecasting. Vol. 17, pp. 611 – 618.
Environment Canada (2010). The total tornado occurrence in Ontario (1979 – 2004). http://www.hazards.ca
Etkin, D., Brun, S.E., Shabaar, A. and Joe, P. (2001). Tornado Climatology of Canada Revisited: Tornado Activity During Different Phases of ENSO. International Journal of Climatology. Vol.21, pp. 915 – 938.
Hammer, B.O., Schmidlin, T.W. (2002). Response to Warnings During the 3 May 1999 Oklahoma City Tornado: Reasons and Relative Injury Rates. Weather and Forecasting. Vol. 17, pp. 577 -581.
National Weather Service (NWS). (1999). The Great Plains Tornado Outbreak of May 3 – 4, 1999. http://www.srh.noaa.gov/oun/?n=events-19990503
National Weather Service (NWS). (2010). Storm Survey Results of the Sibley Iowa EF4 Tornado. http://www.crh.noaa.gov/fsd/?n=tor2010jun25
Schmidlin, T.W., King, P.S., Hammer, B.O. and Ono, Y. (1998) Behavior of Vehicles during Tornado Winds. Journal of Safety Research. Vol. 29, Iss. 3, pp. 181 – 186.
Schmidlin, T.W., Hammer, B.O., King, P.S. and Ono, Y. (2002). Unsafe at Any (Wind) Speed? The Stability of Motor Vehicles in Severe Winds. Bulletin of the American Meteorological Society. Vol. 83, Iss.12, pp. 1821.
Schmidlin, T.W., Hammer, B.O., Ono, Y. and King, P.S. (2008). Tornado Shelter-Seeking Behavior and Tornado Shelter Options Amoung Mobile Home Residents in the United States. Natural Hazards. Vol. 48, No. 2, pp. 191 – 201.
Simmons, K.M. and Sutter, D. (2008). Tornado Warnings, Lead Times, and Tornado Casualities: An Empirical Investigation. Weather and Forecasting. Vol. 23, No.2, pp. 246 – 258.
Storm Prediction Center (SPC). (2010). Tornado Fatalities by Location. http://www.spc.noaa.gov/climo/torn/locations
Ontario Hazards 