Tag Archives: storm

Root Cause Analysis - Incident Investigation

Children Killed When School Hit by Category 5 Tornado

by ThinkReliability Staff

A category 5 (the most destructive) tornado hit Moore, Oklahoma on May 20th, destroying the town and killing 24.  Of those killed, 7 were elementary school children, who drowned when water mains burst in the basement where they were sheltered.

Examining this tragedy can help provide lessons to reduce the risk of this issue happening again.  We can analyze the tornado impact at the most severely impacted elementary school in a Cause Map, in order to visually diagram the cause-and-effect relationships that led to the tragic deaths.

First, we determine the impacted goals.  In this case, all other goals are overshadowed by the deaths of seven  elementary students, and injuries to dozens.  In addition, the school was completely devastated (demonstrating the unbelievable destructive power of the tornado), resulting in early school closure and intense rescue, recovery and cleanup.

To perform our root cause analysis, we begin with the safety goal and ask “Why” questions.  The deaths in this case are reportedly due to drowning, which occurred when children in the basement (a recommended sheltering location in the case of tornadoes) drowned due to water from bursting water mains.  The specific failure mechanism of the failure is not known (and may never be due to the extreme levels of damage) but is likely related to the direct strike of the tornado, which is common in the area (close to the center of tornado alley).

Students who were injured by crushing and asphyxia were in the hallways and bathrooms of the school.  (These are recommended sheltering locations for buildings that don’t have basements.)   It is remarkable that, despite the complete annihilation of the school, students who were sheltered in hallways and bathrooms all survived, thanks in many cases to teachers protecting them with their own bodies.  A 16-minute warning from the National Weather Service combined with carefully rehearsed crisis plans that were put into action, allowed the best possible protection for students in a school without a safe room or storm shelter.

This storm has reignited the discussion about expectations for safety shelters in public places that are prone to natural disasters.  The devastating loss at the school has also raised the safety issue of ensuring that the locations used for shelter are cleared of other potential hazards, such as water mains and fire risks.  Because of the relatively short warning time (16 minutes in this case, which is above average) before a tornado strikes, emphasis on tornado drills and safety plans should continue.

To view the Outline and Cause Map, please click “Download PDF” above.  Or click here to read more.

Root Cause Analysis - Incident Investigation

Deadly Superstorm Slams the US

By Kim Smiley

Hurricane Sandy pummeled the Mid-Atlantic region of the United States on October 29th  and 30th, 2012, leaving more than eight million people without electricity, causing massive flooding and killing over 110 people.  The damage done by this storm was massive and economic impacts have been predicted to be as high as 50 billion dollars.

Why was Sandy so devastating?  This question can be answered by building a Cause Map, an intuitive format for performing a root cause analysis.  A Cause Map is a useful tool for breaking down this complicated issue and can help explain why this storm was unique.

In this example, there are a number of things that combined to made Sandy a unique and especially dangerous storm.  First off, Sandy wasn’t just a normal hurricane.  As hurricane Sandy moved to the north it converged with other weather systems turning into a hybrid storm.  This hybrid storm brought with it a combination of extreme summer weather (strong winds with heavy rains) and winter weather (cold temperatures and snow).  Unusual timing of the different weather systems helped this superstorm form.  Hurricane Sandy hit very late in hurricane system and cold air sweeping down from Canada was colder than typical for this time of year, a combination that proved deadly.  The nature of these converging weather patterns also made Sandy a very slow moving storm so that areas experienced higher rain fall and more damage than they might have with a faster moving system.

Normal hurricanes are powered by the warm, moist tropical air and weaken as they travel north.  They also typically turn to the right and head out to sea.  When Sandy converged with the other systems it became an extra-tropical cyclone and actually strengthened as it hit shore.  The effects of these other weather systems also turned the storm left onto land and it took an unusual path over some of the most heavily populated areas of the US, including NYC,  intensifying the impact of the storm.

The timing of Sandy also impacted the peak flood levels.  Sandy hit during a full moon when tides are at the highest point of the month.  During a full moon, the effects of the moon’s gravity are felt the strongest so tides are higher.  The high winds created by Sandy combined with the full moon resulted in a massive storm surge.

Sandy truly was a Superstorm.  Weather systems that normally don’t exist at the same time converged to create a massive storm that moved in a usual path over one of the most heavily populated regions in the US.  And the storm hit at the worst time of the month for flooding.

For more information click here or here.  To view a high level Cause Map of this issue, click “Download PDF” above.