Monthly Archives: February 2011

Root Cause Analysis - Incident Investigation

Deadly Tiger Attack

By Kim Smiley

On December 25, 2007, a tiger escaped her enclosure at the San Francisco Zoo and attacked three people.  One 17 year old boy was killed and the other two were injured. The enclosure was built in the 1940s and had safely contained tigers for more than 60 years without incident.

So how did this happen?  How did the tiger escape?

A Cause Map can be built using this example to help determine how this incident was able to occur. To begin a Cause Map, the impacts to the organizational goals are first determined and then “why” questions are asked to add causes to the map.  In this case, there was obviously an impact to the safety goal because one zoo patron was killed and two were injured.  The customer service goal was also impacted because the zoo was closed until January 3, 2008 following the incident.  Why was a zoo patron killed?  He was killed because he was mauled by a tiger.  Why was he mauled?  Because the tiger escaped her enclosure and she went after the victims.

Let’s focus on the question of how the tiger escaped her enclosure first.  An investigation was conducted by the United States Department of Agriculture’s Animal and Plant Health Inspection Service, the government body who is charged with overseeing the nation’s zoos.  Based on claw marks and other evidence at the scene, they determined that the tiger jumped from the bottom of a dry moat and was able to pull herself over the fence surrounding her enclosure.  The investigation also determined the fence was lower than typically used around tiger enclosures.  The Association of Zoos & Aquariums recommends that walls around a tiger exhibit be at least 16.4 feet and the fence around the San Francisco Zoo was only 12.5 feet at the time.

The second question of why the tiger went after the boys is not as easy to answer.  A few experts have stated that the tiger didn’t behave in a typical way.  There has been significant speculation in the media that the victims taunted the tiger or provoked her in some way, but nothing has ever officially been determined.

This focus on the behavior of the victims is a good example of some of the issues that can come up during an investigation.  It can be tempting to focus on assigning blame when investigating an incident.  But the real question is “What should we do to prevent this from happening again?”.  Whether or not the boys provoked the tiger, she should never have been able to escape her enclosure.

After the incident, the zoo extensively remodeled the tiger enclosure, adding a much higher fence and with hotwire at the top to prevent any similar incidents from occurring.

Root Cause Analysis - Incident Investigation

The Phillips 66 Explosion: Planning for Emergencies

By ThinkReliability Staff

All business strive to make their processes as efficient as possible and maximize productivity.  Minimizing excess inventory only seems sensible, as does placing process equipment in a logical manner to minimize transit time between machines.  However, when productivity consistently takes precedence over safety, seemingly insignificant decisions can snowball when it matters most.

Using the Phillips 66 explosion of 1989 as an example, it is easy to see how numerous efficiency-related decisions snowballed into a catastrophe.  Examining different branches of the Cause Map highlights areas where those shortcuts played a role.  Some branches focus on how the plant was laid out, how operations were run and how the firefighting system was designed.  Arguably, all of these areas were maximized for production efficiency, but ended up being contributing factors in a terrible explosion and hampered subsequent emergency efforts.

For instance, the Cause Map shows that the high number of fatalities was caused not just by the initial explosion.  The OSHA investigation following the explosion highlighted contributing factors regarding the building layout.  The plant was cited for having process equipment located too closely together, in violation of generally accepted engineering practices.  While this no doubt maximized plant capacity, it made escape from the plant difficult and did not allow adequate time for emergency shutdown procedures to complete.  Additionally high occupancy structures, such as the control room and administrative building were located unnecessarily close to the reactors and storage vessels.  Luckily over 100 personnel were able to escape via alternate routes.  But luck is certainly not a reliable emergency plan; the plant should have been designed with safety in mind too.

Nearby ignition sources also contributed to the speed of the initial explosion, estimated to be within 90 to 120 seconds of the valve opening.  OSHA cited Phillips for not using due diligence in ensuring that potential sources of ignition were kept a safe distance from flammable materials or, alternatively, using testing procedures to ensure it was safe to bring such equipment into work zones.  The original spark source will never be known, but the investigation identified multiple possibilities.  These included a crane, forklift, catalyst activator, welding and cutting-torch equipment, vehicles and ordinary electrical gear.   While undoubtedly such a large cloud of volatile gas would have eventually found a spark, a proactive approach might have provided precious seconds for workers to escape.  All who died in the explosion were within 250 feet of the maintenance site.

Another factor contributing to the extensive plant damage was the inadequate water supply for fire fighting, as detailed in the Cause Map.  When the plant was designed, the water system used in the HDPE process was the same one that was to be used in an emergency.  There is no doubt a single water system was selected to keep costs down.  Other shortcuts include placing regular-service fire system pump components above ground.  Of course, the explosion sheared electrical cords and pipes controlling the system, rending it unusable.  Not only was the design of the fire system flawed, it wasn’t even adequately maintained.  In the backup diesel pump system, only one of three pumps was operational; one was out of fuel and the other simply didn’t work.  Because of these major flaws, emergency crews had to use hoses to pump water from remote sources.  The fire was not brought under control until 10 hours after the initial explosion.  As the Cause Map indicates, there may not have been such extensive damage had the water supply system been adequate.

There is a fine line between running processes at the utmost efficiency and taking short-cuts that can lead to dangerous situations.  Clearly, this was an instance where that line was crossed.

Root Cause Analysis - Incident Investigation

Residential Natural Gas Explosion

By ThinkReliability Staff

The town of Allentown, Pennsylvania suffered severe physical and emotional damage on February 9, 2011, when 5 people were killed and 8 homes were completely destroyed.  The deaths and destruction were believed to be caused by a natural gas explosion, fueled by a 12″ gas main break.  In addition to the impacts to the safety and property goals, the natural gas leak, extended fire, and time/labor by 53 responders also impacted goals.

We can analyze the causes of these impacts to the goals with a visual root cause analysis.  Beginning with the impacts to the goals, we ask why questions to determine the causes that contributed to the incidents.  In this case, there was a delay in putting out the fire because the fire had a heat source from the explosion, a constant oxygen source (the environment) and a steady supply of fuel, as the natural gas continued to leak.  There was no shut-off valve to quickly stop the flow of gas.  It took the utility company 5 hours to finally turn off the gas.  It took 12 more  hours before the fire was completely put out.

The fuel for the explosion and the fire is believed (according to the utility company) to have come from a break discovered in the 12″ gas main.  A 4′ section of pipe, removed on February 14th, is being sent for a forensic analysis to aid in determining what may have contributed to the crack.  It’s possible there was prior damage – such as that from weather or prior excavations.  Most of the pipe in the area was installed in the 1950s, although some is believed to be from the 1920s.  Budget shortfalls have delayed replacing, or even inspecting the lines in the area, and officials have warned that continuing financial issues may continue to delay inspections and improvements,  causing concern with many residents, who suffered a similar natural gas pipeline explosion in 1994.

Because implementation of potential solutions to improve the state of the utility lines in the area may be limited by available funding, it’s unclear what will be done to attempt to reduce the risk of a similar incident in the future.   However, the unacceptability of resident casualties should stir some action so that this doesn’t happen again.

Root Cause Analysis - Incident Investigation

The Phillips 66 Explosion: The Rise of Process Safety Management in the Petrochemical Industry

By ThinkReliability Staff

Many of the industrial safety standards that we take for granted are the direct result of catastrophes of past decades.  Today there are strict regulations on asbestos handling, exposure limits for carcinogens, acceptable noise levels, the required use of personal protective equipment, and a slew of other safety issues.  The organization charged with enforcing those standards is the Occupational Health and Safety Administration – OSHA for short.

OSHA was founded in 1970, in an effort to promote and enforce workplace safety, and their stated mission is to “assure safe and healthful working conditions for working men and women”.  However, there was considerable controversy during its early years as it spottily began enforcing, what was perceived as, cumbersome and expensive regulations.  Notable events in the 1980s, such as the Bhopal and West Virginia Union Carbide industrial accidents, raised OSHA’s awareness that fundamental changes were needed to develop more effective safety management systems.

This awareness led to the rise of what is now known as Process Safety Management (PSM).  This discipline covers how industries safely manage highly hazardous chemicals.  OSHA’s PSM standard lays forth multiple requirements such as employee and contractor training, use of hot work permits, and emergency planning.  Unfortunately PSM was still a work-in-progress during the fall of 1989.

On October 23, 1989, the Phillips 66 Petroleum Chemical Plant near Pasadena, Texas, then producing approximately 1.5 billion of high-density polyethylene (HDPE) plastic each year, suffered a massive series of explosions.  23 died and hundreds were injured in an explosion that measured at least 3.5 on the Richter scale and destroyed much of the plant.  Many of the deficiencies identified at the Phillips 66 plant were in violation of OSHA’s PSM directives; directives which had been announced, but had not yet been formally enacted.

Looking at the Phillips 66 Explosion Cause Map, one can see how a series of procedural errors occurred that fateful day.  Contract workers were busy performing a routine maintenance task of clearing out a blockage in a collection tank for the plastic pellets produced by the reactor.  The collection tank was removed, and work commenced that morning.  However, at some point just after lunch, the valve to the reactor system was opened, releasing an enormous gas cloud which ignited less than two minutes later.

The subsequent OSHA investigation highlighted numerous errors.  First, the air hoses used to activate the valve pneumatically were left near the maintenance site.  When the air hoses were connected backwards, this automatically opened the valve, releasing a huge volatile gas cloud into the atmosphere.  It is unknown why the air hoses were reconnected at all.  Second, a lockout device had been installed by Phillips personnel the previous evening, but was removed at some point prior to the accident.  A lockout device physically prevents someone from opening a valve.  Finally, in accordance with local plant policy but not Phillips policy, no blind flange insert was used as a backup.  The insert would have stopped the flow of gas into the atmosphere if the valve had been opened.  Had any of those three procedures been executed properly, there would not have been an explosion that day.  According to the investigation, contract workers had not been adequately trained in the procedures they were charged with performing.

Additionally, there were significant design flaws in the reactor/collector system.  The valve system used had no mechanical redundancies; the single Demco ball valve was the sole cut-off point between the highly-pressurized reactor system and the atmosphere.  Additionally, there was a significant design flaw with the air hoses, as alluded to earlier.  Not only were the air hoses connected at the wrong time, but there was no physical barrier to prevent them from being connected the wrong way.  This is the same reason North American electrical plugs are mechanically keyed and can only be plugged in one way.  It can be bad news if connected incorrectly!  Connecting the air hoses backward meant the valve went full open, instead of closed.  Both of these design flaws contributed to the gas release, and again, this incident would not have occurred if either flaw was absent.

In hindsight, one can see how multiple problems led to such devastating results.  To easily understand the underlying reasons behind the Phillips 66 Explosion of 1989, a high-level Cause Map provides a quick overview of the event.  Breaking a section of the Cause Map down further can provide significant insight into the multiple reasons the event occurred.  The associated PDF for this case shows how different levels of a Cause Map can provide just the right amount of detail for understanding a complex problem such as this one.

The Phillips 66 explosion was a tragedy that could have been avoided.  The industrial safety standards that OSHA is charged with enforcing aim to prevent future tragedies like this one.  While a gradual safety-oriented transformation has come with some pain and a price tag, few will argue that such standards are unnecessary.  Industrial workers deserve to work in an environment where risk to their health has been reduced to the most practical level.

Root Cause Analysis - Incident Investigation

Aging Natural Gas Pipeline Finally Fails

By ThinkReliability Staff

Few ever contemplate the complex system of utilities surrounding us.  The beauty of our modern standard of living is that usually there is little reason to think about those things.  Those rare cases where power isn’t available at the flip of a switch, or fresh water at the turn of a faucet usually make the local news.

Sadly, the community of San Bruno was faced with much more than simple inconvenience.  On September 9, 2010, an explosion ripped through the suburban community, ultimately killing 8 and destroying or damaging 100 homes.  The explosion was caused by a ruptured natural gas pipeline, and it appears that a slight increase in pipe pressure led to the final failure.  That change in pressure resulted from a glitch in maintenance procedures at a pipeline  terminal.  While ultimately that glitch may have been the “straw that broke the camel’s back”, it is clear from the Cause Map analysis that the straw pile was already fairly high.

Based on National Transportation Safety Board reports, both poor pipe construction and inadequate record-keeping played a major role in the failure.  The pipes, at or near their life expectancy, were already considered too thin by the 1950s’ standards when they were originally installed.  Furthermore improperly done welding made the pipes susceptible to corrosion.  Compounding these issues was the fact that PG&E, the utilities company responsible the pipeline, wasn’t even aware that the San Bruno pipeline had such extensive welding.  This matters because gas pressures are calculated based on a number of inputs, including the construction of the pipeline.  Even that slight increase in pressure proved to be more than the aging pipe could handle.

Natural gas pipelines are fairly extensive in the United States, and with suburban sprawl many communities live close to these pipelines.  In fact, many states have already taken steps to prevent similar events from occurring in their community.  Multiple utilities companies have been mandated to install newer pipelines, as in Texas and Washington.  Additionally, the federal government requires that newly constructed pipelines must be inspected by “smart pigs” – robots able to maintain and inspect pipeline systems.  However, modernizing this aging infrastructure will be expensive for many communities.

Perhaps there are easy, inexpensive interim solutions available.  The Cause Map analysis identifies all causes leading to the explosion, and then provides a systematic method for developing solutions.  Hopefully some of the solutions generated will prevent future disasters, like the one in San Bruno.