TANK FARM INCIDENT: COOPERATION AVERTS A MAJOR DISASTER

BY ROBERT W. LOMAX

What would you do with 66,000 gallons of premium-grade gasoline at a bulk tank storage facility located in an industrial area near the core of a major metropolitan city? The stage was set for a major disaster. However, this incident was successfully mitigated without injury to personnel and without environmental damage.

On June 13, 2001, the ARCO Tank Farm, located at 1652 SW Lander Street, Seattle, Washington, completed a routine inventory of Tank 10. Comparing this inventory with the previous inventory revealed a large discrepancy. Strapping and sounding the tank verified this discrepancy. Strapping a tank-certifying the actual capacity, maximum fill level, and so on-is generally performed after alterations, such as replacing the tank’s roof or floor, have been done. Sounding is simply the gauging of a tank using a brass weighted plumb attached to a tape-measuring reel to determine the level of product in the tank, which is used to calculate the amount of product in the tank. The tape level is then compared with the electronic or mechanical gauge reading to ascertain if there are any differences. After this discrepancy was verified, the tank was visually inspected from the access port on top of the tank. The inspection revealed that the floating pan inside the tank had sunk and that the gasoline product was on top of the floating pan.

ARCO activated its emergency plan using the incident command system (ICS), which included notifying the Seattle Fire Department. ARCO immediately began atmospheric monitoring for percent of oxygen and percent of lower explosive level (LEL). Atmospheric monitoring took place at several locations. In addition to readings taken in the diked areas around many of the surrounding tanks, readings were taken at the east side of the base of Tank 10 at the bottom of the roof access stairs as well as on top of the tank near the hatch access. Monitoring also took place outside the diked areas including adjacent to Tank 10 behind Hose 25, adjacent to the stairs leading up and over the dike wall near Tank 11, and the northwest corner of 16 Ave SW abd SW Lander Street. In addition ARCO began assembling a team and developing an action plan.

PLANNING

On June 14, ARCO held its initial planning meeting to evaluate the hazard and began to develop a plan to mitigate the incident. ARCO assembled a team of personnel that consisted of ARCO representatives (regional manager, terminal manager, technical engineer, public information officer, and safety and yard personnel); Emerald Services (private contractor to transload the product); Matrix (tank contractors for maintenance and pipeline repair); the Seattle Fire Department; and Sound Testing (for air monitoring).

Tank as viewed from outside the concrete dike. Red piping is preplumbed for firefighting foam. (Photos courtesy of Seattle Fire Department.)

On June 15, a final planning meeting was held and a tentative plan was drafted. This plan was revised and updated as the incident progressed. Several alternatives were discussed, and the plan was put into action on June 18. The plan initially included the following procedures and considerations.

Safety would be the top priority for personnel and operations.
The air would be continuously monitored at specific sites in the tank farm for percent of oxygen and percent of LEL.
The product would be removed from the top of the floating pan to an adjacent tank using a diaphragm pump.
The tank would be continuously ventilated to reduce the LEL to less than 5 percent. If the atmosphere permitted it, a worker from Emerald Services would enter the tank and move the pump to the different cells of the floating pan, removing as much product as possible.
The product would be removed under the floating pan through the water draw, a sump that collects water and removes the water or product from the bottom of the tank.
The space under the floating pan would be ventilated.
The floating pan would be cribbed in place, and the tank’s top and bottom would be cleaned.
ARCO and Matrix personnel would enter the tank to inspect the floating pan and complete a root cause analysis.
If an ignition had occurred at ground level, a direct attack on the seat of the fire with foam solution would have been made by Hose 18: Operate the on-site fixed facility foam system, and attach firefighting and/or exposure handlines as necessary to the 2l/2-inch foam connections located around the outside of the tank farm. If an ignition had occurred inside the tank, Hose 25 would have supplied foam solution to the top of the tank, resulting in a foam blanket for fire/vapor suppression inside the tank. In that case, the pre-positioned foam handlines inside the diked area would serve as the initial exposure lines.

ADDITIONAL CONCERNS

The following items were addressed or considered in the planning or operational portions of the incident (in no order of importance):

All injuries are to be immediately reported to the plant manager.
Yard hydrants are to be checked to see if they work.
All yard fittings, hydrants, and hose cabinets are to be physically tested for compatibility with Seattle Fire Depart-ment couplings, and the facility preplan is to be reviewed.
The water supply available at the site is supplied by a 12-inch city water main (134 psi static pressure). In addition, our fireboat is capable of supplying 7,500 gpm at 150 psi and carries onboard 800 gallons of foam concentrate.
The capacity of the existing foam system is to be evaluated-full surface area and rim only.
Weather conditions, especially lightning and other in-clement conditions, are to be monitored.
The load capacity of the fixed roof is to be evaluated to see if it can hold workers-eight persons maximum, and four persons for normal operations.
The following safety measures are to be taken: implement a personnel accountability in and out of the area-passport system and badge system-and ensure that the radios are intrinsically safe and that cell phones and pagers are not used in the warm and hot zones.
Make all aware that items in pockets can fall into the tank and create additional hazards.
The lights inside the tank are to be explosionproof.
Personnel are to wear earplugs in the hot and warm zones.
Constantly check the stability of the floating pan and its position in the tank.
There is to be no hot work on-site during any portion of this incident.
Take into account truck and other vehicle traffic in and around the plant, which will be operating 24 hours a day.

HISTORY

The inspection access at the bottom of the tank, which was opened after the tank was drained. The tank was then cleaned so that ARCO and Matrix personnel could enter the tank for root cause analysis.

Tank 10 was originally constructed in 1940 with a fixed roof; it was retrofitted with an internal floating pan, under the fixed roof, in 1988. The tank measures 60 feet in diameter and is 40 feet high. The capacity is 20,000 barrels or 890,000 gallons. The floating pan is constructed of 3/16-inch steel and has nine cells, one cell in the center with a volumetric size of about 15,400 gallons and eight cells around the perimeter with a volumetric size of about 875 gallons per cell. The cell in the center is 14 inches deep; perimeter cells are 18 inches deep. The floating pan is fitted with adjustable support legs, which can be placed in one of two positions: the low legs (approximately three feet high) can be adjusted to the second position of six feet high. Normally, the legs are in the low position unless the tank is to be cleaned and inspected.

Tank 10 was not provided with a fixed foam system. ARCO maintenance crews, over the weekend, fabricated a 2l/2-inch foam nozzle that was secured to the top of the tank. Hose 25 laid a 2l/2-inch handline from the apparatus, up over the dike, and vertically to the top of the tank, connecting to the foam nozzle. If ignition occurred, Hose 25 was designated to supply foam solution to the top of the tank.

At the time of discovery, the tank contained approximately six feet of product, or about 130,000 gallons. The internal floating pan was resting on its low legs about three feet from the bottom. This divided the total amount of product about three feet below the floating pan and three feet above the floating pan. The vapor space above the product was approximately 96,000 cubic feet; the product surface area was about 2,800 square feet.

SUMMARY OF ACTIVITY

June 18. After a 0700 hours briefing, work was begun to remove the product from the top of the floating pan. Before Seattle Fire Department personnel could work at the tank farm, ARCO had them view a safety and training videotape. Air monitoring was continuous throughout the operation. Prior to any physical operation, Matrix blinded the tank by physically blocking one 12- and two 8-inch pipelines connected to the tank. (Blinding a flange or valve is making sure that a pan blank or a flange blank is inserted into the pipeline or valve flange, which isolates the tank being worked on.) Usually, all inlets and outlets are blinded as a safety precaution (similar to a lockout/tagout).

During the blinding process, the contractor set up ventilation fans and prepared pumps to remove the product from the top of the floating pan. Also during the blinding operation, the fire department positioned one 2l/2-inch foam line to the top of the tank, two 13/4-inch foam handlines in the warm zone, and one 13/4-inch emergency decon line in the warm zone. Fire department apparatus were connected to yard hydrants for a water supply. In addition, the fire department provided four pallets of foam concentrate as a reserve supply as well as an SCBA air-supply apparatus.

The tank as seen from inside the diked area. Access stairs lead to the top and a guard rail around the hatch opening.

After the blinding operation was completed, ventilation and pumping operations started and continued throughout the day. The pumping operation consisted of the following: a pneumatic-diaphragm pump submersed in the liquid product pumped to the top of the tank (approximately 34 feet of lift) down the outside to a hydraulic pump, which completed the aboveground transfer of product to Tank 8. Operations were suspended for the evening about 1900 hours.

June 19. A 0700 hours briefing was held to confirm the plan for the day, which was to continue pumping until most of the product was removed from the top of the floating pan. It was anticipated that, after the pumping operation was completed, someone would enter the tank from the top and physically move the pump from cell to cell to remove as much product as possible. It was estimated that it would take 36 hours to pump the product from the top of the floating pan. The fire department operations chief, Operations 2, and the technical rescue advisors were on-site to assist with planning and implementation. The marine chemist confirmed that no one would enter the tank at least until the following operational period. Pumping operations continued until 2100 hours, at which time all operations ceased for the day.
June 20. At the 0700 hours briefing, it was decided to add two more ventilation fans; there now would be four fans blowing in and one fan exhausting vapor. Pumping with the pneumatic diaphragm pump was resumed. Fire department personnel were briefed at 0800 hours and were on-scene and in position. After approximately one hour of pumping, removal of product from the bottom of the tank through the water draw was begun. This operation was successful; the pumping rate went from about 100 barrels to about 450 barrels per hour. This adjustment allowed for close monitoring of the product being removed and a more accurate accounting of the product in the receiving tank. To prevent creating “void” air space(s) under the floating pan, which could have compromised the structural integrity of the floating pan, pumping from the water draw was stopped when the product level in the tank reached four feet, four inches.

After sounding and strapping the tank to ensure stability, use of the diaphragm pump was discontinued, and a vacuum truck was used to remove the remaining product from the top of the floating pan. The petroleum industry commonly uses a vacuum truck for spills and product recovery. In most cases, vapors are vented into the atmosphere. All but a few gallons of product were left on top of the floating pan. The vacuum truck suction hose was inserted into the top of the tank; the contractor manipulated the hose so that it would reach all of the pan’s cells, virtually eliminating the need for anyone to enter the tank. This effort, coupled with the continuous ventilation, resulted in the tank’s being “blown down” to 0 percent LEL and 20.7 percent oxygen with little or no product left on top of the pan. At this point, the hazard of the incident was successfully mitigated, and the product under the floating roof could be removed in accordance with standard company practice(s). Note: The vacuum truck was not intrinsically safe, even though the use of intrinsically safe trucks is an industry standard. However, the truck was grounded with a grounding rod and a connection strap. Based on data supplied and analyzed by the marine chemist, ARCO was allowed to vent the vapors into the atmosphere during this specific incident.

WHAT WORKED WELL

Unified command. Representatives from each agency were incorporated into the incident command system. This was critical considering the number of agencies involved. In addition, ARCO had recently conducted training exercises using the ICS, so ARCO employees were familiar with their roles and responsibilities, which made for a very smooth operation. ARCO was the incident commander. This was decided and agreed to during the planning meetings, as identified in ARCO’s emergency response plan. This is a unique and extremely rare occurrence within the City of Seattle: ARCO had identified itself as the incident commander in its emergency response plan and had started the planning process just before the Seattle Fire Department arrived.
Assembling information. Information was acquired from as many people as possible. All the information was carefully reviewed, and action plans were developed and altered as needed based on this information.
Daily safety meetings. Daily meetings were held prior to starting work. All agencies met at the command post to discuss safety concerns and review the action plan for the day, limiting the amount of redundancy in disseminating information to all persons.
Immediate notification. Since 9-1-1 was called immediately, the emergency action plan was implemented early. All affected parties knew a problem existed and needed resolution.
Ventilation. Lots of ventilation was key to the successful outcome. It eliminated the atmospheric hazard within the tank. We used high-volume fans, which operated 24 hours per day.
Stabilizing the initial incident. A slow methodical approach to resolution was a major factor in that it did not increase the problem’s magnitude or hazards.
The command post. It was established in an on-site conference room. The plant maps and piping layouts affixed on the walls were very useful in establishing boundaries and control zones.

Accountability. It was excellent. Nametags were posted on a board near the entry point. At a glance, it was easy to determine who were in the different control zones at any given time.
Documentation. It was detailed and continuous throughout the incident. These documents were used to help establish or modify action plans. A running time line was developed each operational day. In addition, the documentation served as an excellent reference of the daily activities, decisions, and progress.
Continuous monitoring of the level in the tank and the surrounding atmosphere. This allowed members to track how much product had been transloaded and how much more product remained in the tank. Closely monitoring levels made it possible to estimate a reasonable time for completing the transfer.

LESSONS LEARNED

Immediately begin monitoring the air at several fixed locations; test for percent of oxygen and percent of LEL.
Engage the services of a marine chemist early in the incident. The information and data he collected in this incident were invaluable in establishing or modifying action plans.
Initially, pumping operations from the top of the tank were slow. Product transloading can be accomplished more quickly by using the water draw. When using water draw with a hydraulic pump, the liquid level in the tank dropped substantially. This saved a considerable amount of time and re-sources.
The vacuum truck should have been placed in line with the submersible pump immediately. The vacuum truck, in combination with these pumps, moved more product in less time that the diaphragm pump initially used to transload the product.
Closely monitor weather conditions and forecasts. Temperature and wind changes directly affect flash point and flammable vapors. A thunder and lightening storm would have immediately shut down all operations, for obvious reasons.

FINAL ANALYSIS

The top of the tank as viewed from the hatch area. The roof is relatively flat and has about three to four degrees of slope.

The major hazard at this incident was the large volume of gasoline vapor in Tank 10, between the surface and the fixed roof, about 34 feet above the surface of the product. After the hazard was mitigated, the tank was emptied and cleaned in accordance with American Petroleum Industry standards. Once the tank was cleaned and the marine chemist certified it was safe for entry, ARCO members and private contractors were permitted to enter the tank and begin a cause analysis. Two of the floating pan cells contained an above-normal level of rust/scale. The welds were cleaned, and a leak test was completed. No leaks were detected. Further examination showed the external roof gutter was lower in the area directly above these two cells, more so than elsewhere around the top of the tank.

The top of the tank has a continuous rain gutter. The down spouts from the gutter were blocked, causing rainwater to enter the tank and sink the floating roof.

Because of the gutter’s being lower in this one area, water on the roof was not able to drain properly. Over a period of time, rainwater filled two cells of the floating pan, causing the pan to sink. The down spouts for the roof gutter were not able to completely drain the water from the top of the roof. A major contributing factor was an above-normal rainfall in the Seattle area during the months of May and June.

The hatch access on top of the tank is about 2 feet 2 4 feet, which is relatively small.

To successfully mitigate this incident, agency cooperation and coordination were critical. The unified command structure helped to ensure a good working relationship.

ROBERT W. LOMAX is a battalion chief in the Seattle (WA) Fire Department, where he has served for 26 years. He was a member of the department’s hazardous materials team for 16 years. He has an associate’s degree in fire command and administration and is a member of the FEMA Puget Sound Urban Search and Rescue Washington State Task Force-1 and Seattle’s Metropolitan Medical Strike Team.