$3 Bolt Causes $2.2 million in Damages to US Submarine

By ThinkReliability Staff

A $3 bolt was left in the main reduction gear of the USS Georgia after a routine inspection.  The extensive damage caused by the bolt resulted in 3 months in the shipyard for the submarine, causing it to miss deployment.  The propulsion shaft was left to operate for two days after sounds indicated that there was something wrong.  This may have increased the damage to the main reduction gear – damage which cost $2.2 million.

How did the bolt end up in the main reduction gear? Why was the propulsion shaft operated for 2 days after damage was suspected?

We can look at the causes that led to this incident in a Cause Map, a visual root cause analysis that clearly outlines cause-and-effect relationships that result in impacts to an organization’s goal.  The first step to building a Cause Map is to determine how the issue impacts the organization’s overall goals.  Here we can consider the US Navy as the organization.  The customer service goal (with the rest of the country as the “customers”) was impacted because the submarine was unavailable for deployment.  The production/schedule goal was impacted because the submarine was in the shipyard for  three months.  The damage to the main reduction gear is an impact to the property goal, and the repairs are an impact to the labor/time goal.  The total cost resulting from this issue was estimated to be $2.2 million.  Once the impacts to the goals have been determined, we can ask why questions to put together the cause-and-effect relationships that led to these impacts.

The bolt was left behind after a routine, annual inspection.  Because of the great potential for damage when foreign objects remain within equipment, detailed procedures are used for these inspections and include a log of all equipment brought into the area and a protective tent to keep objects from falling in.  Details of what went wrong that resulted in the bolt falling into the main reduction gear were not released, but the inspection was reported to have “inadequate prep and oversight” which likely contributed to the issue.

After the propulsion shaft was turned back on, noise indicated that there was a problem.  However, the shaft was operated for two days in a failed attempt at troubleshooting.  It’s likely that this increased the damage to the main reduction gear.  It is unknown what procedures were – or should have been – in place for troubleshooting, but the actions taken as a result of this incident suggest that proper procedures were not followed once the damage was suspected.

In this case, members of the crew who were found to not have performed their job – possibly by not following proper procedure – were punished in varying ways.  It is likely that the investigation went into great detail about whether procedures were adequate, what steps were not followed, and why, and the results also used to improve procedures for the next inspection.

To view the Outline and Cause Map, please click “Download PDF” above.

Fire kills 146, Leads to Improved Working Conditions

By ThinkReliability Staff

146 workers were killed when a fire raced through the Triangle Company, which occupied the top three floors of a skyscraper in New York City.  The workers were unable to escape the fire.  We can examine this incident using a Cause Map, a visual form of root cause analysis, which allows us to diagram the cause-and-effect relationships that led to organizational issues – in this case, the death of 146 workers.

On March 25, 1911 at approximately 4:40 p.m., a fire began on the 8th floor of a New York City skyscraper (one of three floors housing the Triangle Waist Company).  Although it’s not clear what sparked the fire (cigarettes and sewing machine engines are likely heat sources), a large amount of accumulated scraps (last picked up in January) provided plenty of fuel.  There were no sprinklers and the interior fire hose was not connected to a water source.  The fire spread quickly and burned for approximately a half an hour before firefighters extinguished it.

During that half-hour, 146 workers, mostly young women, were killed.  Nearly all of these workers were from the 9th floor of the building.  Workers from the 8th and 10th floor were able to escape to the ground or roof using the stairs, but one of the access doors on the 9th floor was locked.  This left only one set of stairs and elevators, which did rescue many but were overcrowded and the elevator machinery eventually failed due to heat.  Many attempted to escape using the fire escape, which was not built for quick escape (in fact, experts determined it would take 3 hours to reach ground from the Triangle Company floors) and eventually collapsed due to the collective weight, killing those on it in the fall.

Many workers jumped from the 9th floor, but the force of the fall was too great for the fire nets, which mainly broke and the jumpers died.

People were horrified at the conditions in the factories that resulted in these deaths.  In the following years, public outcry resulted in many workers’ rights improvements, including many advances in regulations regarding fire protection and working conditions.  However, these types of issues continue in other countries that have not defined such requirements.

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

113 Killed When a Plane Hit a Hill in Guadeloupe

By ThinkReliability Staff

Flying into a small airport surrounded by mountains at night, in a thunderstorm, with virtually no support from ground equipment proved to be too difficult for even an experienced pilot.

All 113 passengers and crew on Air France Flight 117 were killed when the plane crashed into a hill near the airport in Point-à-Pitre, Guadeloupe on June 22, 1962. The crash occurred in the early morning hours, during a severe thunderstorm.   We can examine the causes of this tragedy in a Cause Map, a visual form of root cause analysis that shows the cause-and-effect relationships that led to an incident  such as this one.  The VHF (very high frequency) omnidirectional range (VOR) indicator, which helps aircraft determine position and stay on course, at the airport in Guadeloupe was not functional.  (It’s not clear if the crew of the Air France flight was aware of this, or how long the equipment had been broken.)  The plane in question was a Boeing 707.

The safety goal was impacted because all people onboard the plane – passengers and crew – were killed.  The plane (valued at $5.5 million) was completely destroyed.  The lack of a working VOR, and the incorrect information provided by the  Automatic direction finder (ADF) can be considered impacts to the customer service goal.  Beginning with the impacted safety goal, we can ask “Why” questions to begin mapping cause-and-effect relationships.   The passengers and crew were killed (and the plane destroyed) when the plane crashed into a hill.

The plane crashed into a hill because the airport was surrounded by mountains, and the plane strayed off the let down track, which it should have used for its approach to the airport.  The pilot went off track because he was using a visual approach, probably due to the fact that the VOR was not providing data since it was not working.   The pilot was unable to see the track due to low (10 km) visibility and since it was early morning (~4 a.m.).  In addition, the plane received incorrect position indication from the ADF, which appeared to malfunction as a result of the severe thunderstorm in the area.

This incident resulted in concern from pilots of substandard landing conditions at certain airports.  More care is now taken with take-off and landing during inclement weather, poor visibility, or conditions that result in landing with decreased equipment support.

To view the Outline and Cause Map, please click “Download PDF” above.

Deadly Sawmill Explosion

By ThinkReliability Staff

An explosion and subsequent fire at a sawmill in British Columbia has killed two workers and injured two dozen more.  Although the cause of the explosion is not known, there have been five explosions linked to wood dust in British Columbia since 2009.

A dust explosion results from the presence of combustible dust, such as that created by the sawmilling process.  In order for an explosion to occur, the dust must be dispersed into the air but confined by a structure in the presence of oxygen and a spark.  (Learn more about dust explosions.) 

To view all the causes that contributed to this tragic explosion, we can examine the incident in a Cause Map, or visual root cause analysis.  We begin with the impacts to the goals. The employee deaths and injuries are an impact to the safety goal.  This is the primary focus of any issue that results in human death or injury.  In addition, the environmental goal was impacted as the smoke migrated to the nearby town.  The production goal was impacted due to the shutdown of the facility.  The property goal was impacted due to destruction of the sawmill, log processing facility, and sorting facility.  Lastly, the investigation and cleanup will impact labor goals.

Once we have determined the impacts to the goals, we can ask why questions to determine the cause-and-effect relationships that led to the incident.  In this case, the injuries were due to the fire.  The fire may have been caused by a dust explosion (explosion due to natural gas leak has been ruled out).  In order for a dust explosion to occur, five factors are necessary: 1) presence of combustible dust, 2) oxygen, 3) dust is dispersed into the air, 4) dust particles are confined, and 5) the mixture is ignited.

In this case, the ignition source is not known and, due to the damage at the facility, may never be conclusively determined.  Similarly, the cause that resulted in the dust being dispersed may also not be known.  The oxygen must be present for worker safety and the dust is confined because it is held within a closed structure.  The dust is present because it is created during sawmilling operations.  What makes a dust combustible depends on the properties of the dust.  This mill was processing pine beetle wood, or wood that was ravaged by beetles.  This makes the wood drier, which results in a drier, finer, more combustible dust.  Thorough cleaning of any facility that creates potentially combustible dust is a necessity – inadequate cleaning (including dust that may gather on hard-to-access surfaces, such as the ceiling) increases the possibility of an explosion.  The union believes that cleaning has been reduced as a result of the economy.

Local government has begun inspections of saw mills but are asking plants to examine potential dust and ignition sources. Reducing dust and ignition sources are the most effective way to reduce risk of dust explosions.  Other solutions being considered include adding water to the air to increase humidity and increased ventilation, which can reduce the confinement of the dust and increase cleanliness.

To view the Outline and Cause Map, please click “Download PDF” above.