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Storage & Terminaling image A THE American Petroleum Institute (API) and National Fire Protection Association (NFPA) expect to issue official responses early this year to the US Chemical Safety Board's (CSB) call for new public-protection measures at oil and gas production sites.

On October 27, CSB released a new study of explosions at oil and gas production sites across the United States, identifying 26 incidents since 1983 that killed 44 members of the public and injured 25 others under the age of 25.

The report examined in detail three explosions that occurred at oil and gas production facilities in Mississippi, Oklahoma, and Texas, that killed and injured members of the public between October 2009 and April 2010.

The CSB report found that children and young adults frequently socialize at oil sites in rural areas, unaware of the explosion hazards from storage tanks that contain flammable hydrocarbons like crude oil and natural gas condensate. The unintentional introduction of an ignition source (such as a match, lighter, cigarette, or static electricity) near tank hatches or vents can trigger an internal tank explosion, often launching the tank into the air and killing or injuring people nearby.

Storage & Terminaling image B The report identified regulatory gaps at the federal and state levels and called on the US Environmental Protection Agency (EPA) and state regulatory bodies to improve current safety and security measures at exploration and production sites such as warning signs, full fencing, locked gates, locks on tank hatches, and other physical barriers. The report also called on state regulators in Mississippi, Oklahoma, and Texas to require safer, modern tank designs that reduce the likelihood of an internal tank explosion if an ignition source is inadvertently introduced nearby.

CSB's recommendations to API (2011-H-1-R05) call for creation of a new standard or amendments to existing standards covering exploration and production facilities to:

  • Warn that storage tanks at unmanned facilities may be subject to tampering or introduction of ignition sources by members of the public, which could result in a tank explosion or other accidental release to the environment.

  • Recommend the use of inherently safer storage tank design features to reduce the likelihood of explosions, including restrictions on the use of open vents for flammable hydrocarbons, flame arrestors, pressure vacuum vent valves, floating roofs, vapor recovery systems, or an equivalent alternative.

  • Require security measures at least as protective as API 2610 to prevent non-employee access to flammable storage tanks at upstream E&P sites, including such measures as a full fence surrounding the tank(s) with a locked gate, hatch locks on tank manways, and barriers securely attached to tank external ladders or stairways.

  • Require that hazard signs or placards be displayed on or near tanks to identify the fire and explosion hazards using words and symbols recognizable by the general public.

  • Recommend that new or revised mineral leasing agreements include security and signage requirements.

CSB recommends amending NFPA 30 (Storage of Liquids in Tanks — Requirements for all Storage Tanks) as follows:

  • Remove the term “isolated” from the current wording of the standard and replace it with a more descriptive term, such as “normally unoccupied.”

  • Remove the words “Where necessary” from Security for Unsupervised Storage Tanks, Chapter 21.7.2.2.

  • Add a reference to a relevant security standard that offers specifications on fencing, locks and other site security measures.

  • Add a definition of security encompassing requirements such as fencing, locked gates, hatch locks, and barriers.

API, NFPA reaction

API president/CEO Jack Gerard tells Bulk Transporter that API's committees will review the recommendation and determine what changes may need to be proposed to the appropriate standard.

“At this time, we do not anticipate creating a new standard, and will advise CSB staff once a project plan has been developed and approved,” he says.

He notes that API's exploration and productions standards RP 12R1 (Recommended Practice for Setting, Maintenance, Inspection, Operation, and Repair of Tanks in Production Service), RP 74 (Recommended Practice for Occupational Safety for Onshore Oil and Gas Production Operation), and RP 75L (Guidance Document for the Development of a Safety and Environmental Management System for Onshore Oil and Natural Gas Production Operations and Associated Activities) “all address issues related to site safety.”

Bob Bennedetti, principal flammable liquids engineer for NFPA, says a committee will meet sometime in the first quarter of this year to review the recommendations and determine what changes, if any, are appropriate.

Under Section 8.7.3 of the report, CSB analyzed API's RP 74, saying that it “was developed in response to a CSB safety recommendation that resulted from a 1998 explosion that killed four workers at a Louisiana oil and gas production facility. It includes safety guidance for fire prevention and protection, such as designating areas where there are fire hazards, prohibiting smoking and ignition sources within those areas, posting conspicuous warning signs, and properly labeling tanks that contain flammable liquids. Appendix A of API 74 includes a checklist of questions for periodically assessing safety at oil production facilities. Some questions, for example, suggest that operators verify the posting of ‘No Smoking,’ ‘No Trespassing,’ and/or ‘Authorized Personnel Only’ signs at oil site entrances.

“Other checklist questions ask whether ‘ladders are caged when over 20 feet,’ if the ‘access opening to the ladders [is] provided with a swinging gate or chain closure,’ and whether ‘tank thief hatches seal or are in good repair.’

“Beyond these appendix questions, however, the main sections of API 74 include no guidance on requirements for fencing, physical barriers, or security gates to prevent access to tank catwalks and tank hatches; hatch locking mechanisms; or specific tank explosion warning signs to prevent fatal incidents due to unauthorized entry. As currently written, API 74 primarily focuses on occupational safety requirements, containing only limited recommendations for public protection.”

Under Section 8.7.4 of the report: “Following the 9/11 attacks, the API assessed the E&P sector for security vulnerabilities. The API assessment found most E&P facilities produce low quantities of product; over 75% of US oil wells are ‘stripper’ wells that produce fewer than 10 barrels of oil daily. Most are located in rural areas. To provide safety and security, API suggested the use of the following standards: RP 49, Drilling and Well Servicing Operations Involving Hydrogen Sulfide; RP 54, Occupational Safety for Oil and Gas Well Drilling and Servicing Operations; RP 74; Publication 761, Model Risk Management Plan for E&P Facilities. Of these standards, only API 54 recommends labeling of tanks ‘to denote their flammable contents’ (API 54 Section 8.4.4).”

Under Section 8.7.6 of the report, CSB said that “NFPA 30, the Flammable and Combustible Liquids Code (2008), applies to the storage, handling, and use of flammable and combustible liquids, including waste liquids. Section 21 requires the use of flame arrestors when storing certain flammable liquids (Class 1B and IC) and Annex A suggests their use to stop the propagation of a flame inside a tank. Section 22 has requirements for storing liquids in aboveground tanks including location and installation, normal and emergency venting, fire protection, spill control, collision protection, and maintenance.

“In the 1990 edition, NFPA added subsection 2-9.3 which states that ‘unsupervised, isolated aboveground storage tanks shall be secured and marked in such a manner as to identify the fire hazards of the tank and its contents to the general public.’ The 2008 edition further states ‘where necessary, to protect the tank from tampering or trespassing, the area where the tank is located shall be secured.’ The NFPA justified the provision based on ‘several recent tank explosions caused by youngsters who have trespassed in and on tanks.’ However, the code has no specific requirements for security or fencing. The CSB learned that 44 states have adopted a version of NFPA 30 (ranging from the 1990 to 2008 editions).”

Safeguarding lives

CSB chairman Rafael Moure-Eraso says that as the demand for domestic energy resources continues to grow and the number of active extraction and production sites continues to rise steadily, “it is important to ensure that these sites have the appropriate safeguards to save young people's lives.”

On October 31, 2009, two teenagers, aged 16 and 18, were killed when a storage tank containing natural gas condensate exploded at a rural gas production site in Carnes, Mississippi. Six months later, a group of youths were exploring a similar tank site in Weleetka, Oklahoma, when an explosion and fire fatally injured one individual. Two weeks later, a 25-year-old man and a 24-year-old woman were on top of an oil tank in rural New London, Texas, when the tank exploded, killing the woman and seriously injuring the man. The CSB deployed investigators to all three sites to collect information on the incidents.

Investigators found that the three accidents occurred in isolated, rural wooded areas at production sites that were unfenced, did not have clear or legible warning signs and did not have hatch locks to prevent access to the flammable hydrocarbons inside the tanks.

“After reviewing the work of our investigators I believe that these incidents were entirely preventable,” Rafael Moure-Eraso says. “Basic security measures and warning signs — as well as more safely designed storage tanks — will essentially prevent kids from being killed in tank explosions at these sites.

The CSB's investigation found a few major cities and some states, such as California and Ohio, already require varying levels of security for oil and gas production sites, such as fencing, locked or sealed tank hatches, and warning signs. As a result, California did not appear to have any fatal tank explosions between 1983 and 2011. However, many other large oil and gas producing states have no such requirements. The major oil producing states Texas and Oklahoma require fencing and warning signs for certain sites that have toxic gas hazards but not for all sites with flammable storage tanks.

“Oil and gas storage sites are part of the landscape in many rural American communities; hundreds of thousands of similar sites are located across the country,” says CSB Lead Investigator Vidisha Parasram. “It was a concern to discover that issues related to public safety are rarely considered prior to placement and design of these sites. In many cases, sites can be as close as 150 to 300 feet from existing buildings such as residences, schools, and churches, and still lack any meaningful warnings or barriers to prevent public access.”

Among the six formal safety recommendations in the report, the Board urged that state regulators require the use of inherently safety tank design features such as flame arrestors, pressure-vacuum vents, floating roofs, and vapor recovery systems. The safety measures, which are similar to those already in use in refineries and other downstream storage tanks, reduce the emissions of flammable vapor from the tanks or otherwise prevent an external flame from igniting vapor inside tanks.

“The goal of this investigative study is to issue recommendations that will effectively address the current gaps that exist at the state and federal level,” Moure-Eraso says. “As I have seen firsthand, these sites can be dangerous to the people who live and work in these communities and should be properly designed and protected.”

Safety bulletin

The Board recommended that EPA issue a safety bulletin warning of the explosion hazards of storage tanks, describe the importance of increased security measures such as fencing, gates and signs, and recommend the use of inherently safer storage tank design. Similarly, the CSB's recommendations seek to address the current gaps in regulations and codes in Mississippi, Oklahoma and Texas.

The report found that at typical E&P sites, crude oil and natural gas are pumped from underground hydrocarbon reservoirs to the surface. The well stream is connected to a piping system that transports hydrocarbons to an oil-gas separator where gas and water are removed from crude oil. The oil is then transferred to storage tanks in a tank battery until it is pumped into a transport truck for eventual sale.

In states where vapor recovery systems are not mandated, oil tanks are usually equipped with a tank hatch and an atmospheric vent on the surface. Oilfield workers regularly check liquid levels through the hatch, which is accessible by a walkway or catwalk. The oil-gas separator also contains an atmospheric vent that releases hydrocarbon vapors.

Atmospheric storage tanks with a 210-barrel capacity — which were involved in two of the three explosions investigated by the CSB — are commonly used to store crude oil and condensate at E&P facilities throughout the United States. These tanks are rated for petroleum liquids with a vapor pressure of less than 0.5 psi and are selected “based on vapor pressure, flash point, potential for explosion, temperature, and specific gravity.” If circumstances change inside the tank and the internal pressure increases significantly above its pressure rating, the tank loses its structural integrity and fails.

According to CSB, inherently safer tank design could have prevented the formation of a flammable atmosphere inside the tanks and likely prevented the three incidents investigated, as well as the 23 other similar tank explosions that were identified. It listed the following examples of tank design features that can be used at E&P facilities to isolate and contain the flammable vapors in order to prevent a vapor space explosion.

  • An internal floating roof is a design feature where a roof floats on top of a flammable liquid, reducing the hydrocarbon vapor to low concentrations well below the flammable limit. In the past, smaller diameter tanks (eg, less than 30 feet in diameter) could not practically use floating roofs because of stability issues. Today, due to API 650, relaxed buoyancy requirements for small tanks and the development of new composite floating roof materials, floating roofs can be installed in new or existing tanks as small as 8-10 feet in diameter. Currently, most E&P storage tanks have fixed roofs — a less costly alternative to an internal floating roof.

  • A second inherently safer design feature is the use of pressure vacuum (PV) relief valves. Pressure vacuum relief valves are commonly used on fixed roof tanks to minimize evaporation losses. However, they effectively isolate ignition sources, essentially acting as flame arrestors, so that external ignition sources nearby will not flash back to the vapor space, causing a tank explosion. The valves are designed to prevent the accumulation of pressure or vacuum which could compromise the tank integrity. However, most existing E&P oil storage tanks use open vents when storing flammable liquids. Only those tanks located in areas with strict air pollution rules (eg, in California) avoid the use of open atmospheric vents. The likelihood of a flash back can be significantly reduced by the use of PV relief valves.

  • A third design option (one which is recommended for tanks located in urban areas of Ohio) is the use of an actual flame arrestor — a device that extinguishes a developing flame outside a tank, preventing it from entering the vapor space. The flame arrestor forces a flame front through narrow channels that inhibit the propagation of the flame. Both flame arrestors and pressure vacuum valves are similar in function in that they act as barriers to flame propagation from outside the tank into the vapor space.

  • A final option is the use of a vapor recovery system — a closed system that keeps flammable vapors inside the tank. This system requires the entire tank (tank hatches, atmospheric vents, and all tank orifices) to be sealed and isolated from the atmosphere, thus preventing external ignition sources from entering the vapor space. The internal vapors are either recovered for future use or routed to a flare system. Vapor recovery systems are required for tanks located in poor air quality zones in California. End of feature

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