What Causes Storage Tanks to Collapse?

Catastrophic tank failures are those that seemingly happen in the blink of an eye. An oil tank could be working just fine. However, if it’s struck by lightning, a catastrophe could be imminent, particularly if the tank has not been grounded. Tanks may also slowly fail over time. If a tank is showing early signs of pitting and corrosion, there’s still time to remedy the situation before the tank weakens so much it eventually fails.

Improper Construction

One of the most infamous storage tank failures occurred 100 years ago in Boston. A poorly designed, constructed and maintained storage tank burst in Boston’s North End neighborhood on Jan. 15, 1919, releasing 2.3 million gallons of molasses. The sticky liquid crested as high as 25 feet high as it swept through Boston’s streets, killing 21 people and injuring another 150 in its path. A bevy of lawsuits was filed in the wake of the Boston Molasses Disaster, leading to a six-year investigation into the tank failure. This led to stricter regulation and construction standards for steel and concrete (PS Magazine).

Modern storage tanks should adhere to API 650 and API 653 standards to ensure structural integrity. The tanks should also be thoroughly inspected before they go into service. According to the EPA, a properly designed and maintained storage tank will break along the shell to top seam. This design helps limit contents being spilled and fire outbreaks from spreading.

Weather

With their violent winds and torrential rainfalls, hurricanes are Earth’s most destructive storms, wreaking havoc in their wake. Many storage tanks containing oil and dangerous chemicals are located along the Gulf Coast, which is regularly battered by hurricanes. Volatile chemicals and destructive storms can be a dangerous and potentially deadly mix. 

Hurricane Harvey, which struck the coast in the summer of 2017, unleashed 51.9 inches of rain in Houston. This area is the home to many crude oil and chemical storage tanks, a lot of which are equipped with floating roofs that are designed to hold up to 10 inches of rain without draining. Harvey’s record rainfall was too much for the roofs of these tanks, at least 15 of which failed and released a combined 3.1 million volatile chemicals into the atmosphere, according to a Houston Chronicle article.

The most common weather-related hazard to storage tanks is lightning. According to an NFPA report, lightning was the heat source for one-third of fires at outside storage tanks. Lightning doesn’t have to strike a tank directly for it to catch fire, it just has to be in the nearby vicinity. There are ways to mitigate the effects of a lightning strike on a storage tank. As far back as the 1920s, experts have been preaching the importance of grounding tanks to protect them from lightning.

Seismic Zones

A magnitude-9 earthquake and tsunami rocked Japan on March 11, 2011. As a result of the powerful earthquake, many of the region’s oil and storage tanks were damaged. Oil storage tanks collapsed due to the tsunami’s strength while the sustained shaking from the earthquake caused sinking roofs to fail. The after effects of the Tohoku earthquake was felt for years. In 2013, Reuters reported that there were record radiation readings near Fukushima nuclear plant’s contaminated water tanks.

Storage tanks should be designed with seismic zones in mind. Some areas in the United States are closer to fault lines and therefore in areas more prone to earthquakes. Storage tanks should be designed accordingly to withstand a potential earthquake, following API 650 Appendix E guidelines. Tanks in Seismic Zone 2 or greater, like in California, Oregon, and Washington, should be checked for seismic stability based on the rules of the applicable standard.

Operational Accidents

Some tank explosions are triggered by human error or interference. A worker was cutting open a decommissioned tank at an oil and gas site with an oxygen-acetylene torch. The tank happened to have a leak along the bottom seam.  The flammable material inside the tank ignited and an explosion occurred at a West Virginia site in May 2018. Three workers sustained burns.

In a 2014 incident, OSHA reported that an employee was welding a catwalk onto a tank when he ignited the vapors from used oil. The employee, who wasn’t wearing fall protection gear, was ejected from the top of the tank and killed.

Pressure

Overfilling a tank can create excessive pressure. If the pressure builds up too much, the tank can rupture.  Heating up and cooling down a storage tank can both cause overpressurization or a vacuum failure. Liquid entering a tank causes displacement of vapors. Vents in the tank help alleviate pressure changes by allowing a safe way for vapors to leave the tank. Vents also allow air to fill the tank, so a vacuum is not created.

Volatile liquids evaporate easily at normal temperatures.  Volatile liquids can flash when they are pumped into a tank, producing additional vapors that can cause a buildup in pressure.  Gasoline, acetone, ethanol, and bromine are all examples of volatile liquids and ones that might be found in storage tanks.

In 1983, there was a gasoline tank explosion at a Newark, NJ facility. The overfilling of a floating roof tank spilled 1,300 barrels of gasoline in the tank dike, according to a report. Because of this, a vapor cloud formed and was ignited. The explosion was so powerful it was felt by people within a 100-mile radius.  It killed one person and injured 24.

Sabotage

Chemical storage tanks are a tantalizing target for terrorists and thieves. Because of the volatile chemicals they contain, to terrorists they are just a powder keg waiting for a match to strike and cause a devastating explosion. The chemicals are also valuable to thieves who might, for instance, steal anhydrous ammonia – a key component for methamphetamine. People should follow OSHA regulations 1910 Subpart H 1910.111 anhydrous ammonia regulations.

A real-life example of what federal officials said appears to have been sabotage was the fertilizer plant explosion in West, TX on April 17, 2013. The blast killed 15 people, including 12 emergency responders, injured about 260, and damaged or destroyed 150 buildings as burning debris scattered over a five-block radius, according to a U.S. Chemical Safety and Hazard Investigation Report.

After the explosion, it was discovered that OSHA hadn’t conducted a full safety inspection at the facility since 1985. The plant also didn’t have a fire detection system to alert emergency responders or an automatic sprinkler system, according to a federal report. The Bureau of Alcohol, Tobacco, Firearms and Explosions stated that the fire was deliberately set.

There are many different ways a tank can fail but following regulations and standards and vigilantly inspecting and maintaining tanks are the best ways to prevent tank failure.

Erin Schmitt is the media director/technical writer for Pittsburg Tank & Tower Group.