Storage Tank Boilover in Nicaragua Dies Unchallenged
Wednesday, December 21, 2016
Williams Fire & Hazard Control, a Tyco Fire Protection Products business, was ready, willing and able to extinguish the aftermath of a crude oil boilover in Nicaragua that left two 150-foot diameter storage tanks in flames. However, the decision by the local oil company was to let the remaining fire die a slow, natural death.
“The changing dynamics of the scenario kept taking the ball out of our hands,” said Chauncey Naylor, WF&HC director of emergency response and training. “You have a plan but then the situation changes dramatically. So you have to make a new plan.”
For Naylor, the biggest triumph of the entire experience was predicting the boilover to within 40 minutes, giving authorities time to clear any personnel in harm’s way.
“According to company representatives the crude oil tank boiled over four times in rapid succession, but none of the product left the containment area,” Naylor said.
He also takes great pride in that the entire incident, from beginning to end, was handled without a single injury.
The fire occurred August 17 at a fuel terminal in Puerto Sandino, Nicaragua, about 45 miles northwest of Managua. A press release by the terminal owners states the initial report came at 4 p.m. Texas-based WF&HC was contacted about an hour later, Naylor said.
Only one of the two tanks sharing a common containment dike was ablaze at that point. The fire involved flames rising from the circumference of the tank’s floating roof where a rubber seal joins it to the tank shell. Geodesic domes designed to keep rainfall separate from the crude topped both tanks.
Naylor and the responding WF&HC team hopped a charter flight from Houston to Managua. Long before they arrived, the seal fire turned into something much worse.
“The seal fire burned for four hours before it finally failed that geodesic dome,” Naylor said. “The dome went down on the lightweight floating roof and sank it.” Fire now extended across the full surface of the exposed crude
Ordinarily, WF&HC does not recommend using cooling water on a tank fire, Naylor said.
“There is no effect of cooling the contents,” he said. “All it does is fill up the dike with water.”
However, this case was different. The second tank in the dike contained naphtha and stood only 120 feet away from the one already burning. That made it an exposure in need of immediate protection.
“Tank two was already showing signs of overheating,” Naylor said. “But the firefighters weren’t able to effectively cool it because the containment dike made it difficult to find a good position to shoot cooling water from.”
Meanwhile, the burning crude tank slowly moved toward a potentially dangerous phenomenon known as a boilover.
Most crude oil contains water. While in storage, most of that water sinks to the bottom of the tank. What makes a full surface fire so hazardous is that it steadily heats the crude beneath it, sending a thermal wave down through the contents to the water below.
At 212 degrees Fahrenheit, water turns to steam – in atmosphere at sea level. In this case, 25 to 30 feet of crude oil sat atop the water which increased its boiling point and expansion rate. When the water turned to steam, large volumes of heated, burning crude was ejected in the most aggressive way possible, possibly covering a radius several times the dimension of the tank.
To the credit of his Nicaraguan counterparts, firefighters on the scene recognized the threat the expanded fire posed, Naylor said.
“They were familiar with the term boilover and took it seriously. “There are companies in the oil business that don’t know what a boilover is.”
With the WF&HC team still in flight, Naylor was asked to estimate the time left before a possible boilover. The calculation involves balancing the gravity of the product against its boiling range and product level.
“They had a pretty good idea of what kind of effective changes in the fire to look and listen for,” Naylor said. “They got their people out of the way.”
When Naylor and the WF&HC team arrived at the terminal authorities congratulated him on his accuracy. The predicted boilover had occurred. Firefighters now had two storage tanks ablaze, a containment dike full of burning crude and numerous manifold fires from ruptured piping.
The equipment Naylor brought from Houston included three portable monitors known as Daspit tools, complete with ground stands, other associated nozzles and some proportioning equipment. Unfortunately, boilover damage now radically diminished any access to available water.
“Most of it ran to monitor stations in the containment area,” Naylor said. “The boilover had effectively breached everything with regard to firefighting water.”
Two 2,500 gpm firewater pumps were left running to avoid losing suction. But with no safe access to any isolation valves, the firefighters could only watch while the water flowed freely from various ruptures, further filling the dike.
The charter airline went to work again. The 8,000 gallons of three percent AR-AFFF foam available at the terminal and brought in from nearby refineries would not be enough to handle two burning 150-foot storage tanks.
“The client arranged for 18 totes of THUNDERSTORM 1x3 to be transported immediately from headquarters in Port Arthur,” Naylor said. “So, naturally, we had some time to wait before it arrived.”
It was decided to tap the firewater system at its source – the pumps. Large diameter 7¼–inch hose would be fitted to both of the available pumps and extended nearly 1,500 feet to supply the three Daspit tools already on the scene. Six 350-pound PKW dry chemical wheeled units would be used to address the various burning pump seals, flange gaskets and other pressure fires.
A third flight was chartered to bring in 3,200 feet of LDH and associated appliances. Everything needed for the extinguishment attempt was expected to be in place by noon the next day.
“We had a good plan,” Naylor said. “The containment area fire burned itself out as expected that evening. We laid our heads down figuring to get up before first light.”
The light that greeted them arrived a little early. About 4:30 a.m. Naylor was advised by phone that the naphtha tank had suddenly failed.
“It didn’t split,” Naylor said. “It folded in like any other tank might normally do. But the tank went from 50 feet tall to about half that almost instantly.”
Fifteen feet of product was introduced to the dike so suddenly that it actually slopped over the dike wall at several locations.
“The containment dike was on fire again, and the immediate area outside the dike on two sides was burning,” Naylor said.
Local firefighters used a crash truck to quickly knock down the flames outside the dike. Concern turned back to the crude tank.
“After all, that one had been burning longest,” Naylor said. “It was slowly folding but it was holding its integrity.”
Time had come to reevaluate. Naylor put two options before the owners and federal authorities. One, continue with the extinguishment as planned. Or, two, in consideration that not much product was left, simply let the fire burn out in its own time.
“The cost of the product saved would not have outweighed the cost of extinguishment,” Naylor said. “My concern was for the people who would have to deal with the aftermath.”
By the time firefighters would be prepared to attempt extinguishment no more than several feet of product would be left in either tank, Naylor said. With only four tanks in the terminal originally, there was no way to transfer the remaining product which would be exposed to the atmosphere.
“In order to get back in business, the owners would have to dismantle the burned up motors and change the pump system to get these other tanks that survived back online,” Naylor said. “Before you can do that you’re going to have to clean up all this exposed flammable liquid using specialized vacuum trucks.”
Putting out the fire at this point would create a bigger hazard than letting the fire take its course, he said. He estimated the business interruption before rebuilding could start would be a minimum of six weeks.
“It’s not our method of choice to deal with tank fires,” Naylor said. “In this case, it was the right thing to do.”
Getting the owners onboard was easy, he said. It represented a substantial cost savings as opposed to pulling the trigger on the extinguishment option. Convincing federal officials was more difficult.
“We visited with a special board set up by the president of Nicaragua,” Naylor said. “They were not satisfied that the fire was not being extinguished. I didn’t have a problem with that.”
When the discussion reached a stalemate the government assigned a task force to visit the fire scene, he said.
“Once they saw the devastation from the initial boilover, the tank collapse and the effect on all the equipment associated with the terminal, they realized that option two was the most viable and safest,” Naylor said.
However, the terminal fire at Puerto Sandino had one more surprise for emergency responders. That afternoon a loud rumbling developed in the naphtha tank. Suddenly, the product left in the tank launched hundreds of feet into the air.
“What we think happened was a steam explosion,” Naylor said. “There was so much fire around the tank for so long. There was water in the tank from all the cooling that had been done.”
The effect was much like the boilover in the crude tank, except that naphtha is a light end product with a high vapor pressure, he said. Water seeping into the still burning tank settled beneath the naphtha and turned to steam when increasing heat reached it.
“It was all launched into the air and consumed,” Naylor said. “No burning liquid came down.”
An unexpected benefit from this final eruption was that the remaining naphtha was consumed much faster than waiting for the fire to finish it.
“We sat there for two hours watching that thing die,” Naylor said. “The big steam flash was its last hurrah.”
With the naphtha tank out, the only glow visible that night was from inside the crude oil tank. The WF&HC team left before final extinguishment the next morning, but not without leaving the remaining firefighters set up to deal with it.
“We showed them all the equipment and how to use it,” Naylor said. “The next morning they addressed that crude oil tank with some foam, just to knock the smoke down. They ran it for about 20 minutes and it was all over.”
Naylor said the Puerto Sandino job was only the second time in WF&HC history that it was decided to let a fire burn itself out.
“It was all based on post extinguishment safety,” he said. “That way they could go right back to work without any hazards.”
And they did. The next morning workers were already pulling and replacing necessary equipment needed to get back the terminal back in service.
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