Article Archive
Trelleborg Offshore
Spheres provide vapor barrier alternative
Vol 26 Summer

Historically, Trelleborg Offshore is a supplier of buoyancy products and other lightweight composite solutions to the offshore oil and gas industry. Trelleborg’s new fire and vapor suppression spheres apply that material technology to another area of industrial concern – fire fighting, specifically large storage tank fires.

Applied by itself as a semi-permanent vapor barrier or as an additive to fire fighting foam, the spheres create a vapor barrier between both polar and non-polar flammable liquids and the vapor space above, said Bob Kelly, Vice President of Global Customer Solutions for Trelleborg Offshore.

Because the product is capable of handling high temperatures and has an oil repellant outer coating, the barrier lasts indefinitely compared to the temporary barrier that traditional foam provides. 

“The reason we call it foam is that it behaves in a similar way as water-based foams for fighting tank fires that create a vapor barrier using bubbles. However, Trelleborg fire suppression spheres work without the problems of freezing or bubble degradation or any use of fluorochemicals,” Kelly said.”

The vapor and fire suppression spheres are a development of Trelleborg’s core technology marketed as a vapor suppressant and fire fighting agent for large storage tanks containing hydrocarbon polar and non-polar fuels. The individual spheres are applied dry and self-assemble into a foam-like structure that is lighter than both oil and water.  The resulting ‘foam’ suppresses vapors to the point of extinguishment of liquid hydrocarbon fires if applied properly. It is an advanced composite material that is essentially lightweight spheres varying from -to-½ inches.

Trelleborg’s vapor and fire suppressant spheres have several advantages over traditional AFFF foams.  Since the spheres do not rely on water to put out fires, they are most attractive in application, in regions of the world where low temperatures pose freezing issues (think Alaska in winter) and where water is scarce (think West Texas and Saudi Arabia). In addition they are of particular benefit where a passive solution to fire hazards is deemed appropriate or where the environmental effects from fluorochemicals in traditional foam is a particular concern.

The new product underwent extensive testing in September 2010 conducted by LASTFIRE, a consortium of international oil companies whose charter is to review the risks associated with storage tank fires and develop best practices for the industry. The testing, held at the Centro Jovellanos fire training facility in Asturias, Spain, was supervised by Resource Protection International, an independent consulting firm acting as LASTFIRE Coordinators. LASTFIRE carries out research and testing on a range of new and existing technologies as part of their commitment to ongoing advancement of knowledge and understanding of large storage tank fires and how to respond to them.

Testing included 17 different tests for fire suppression, vapor suppression and boil over delay. The hydrocarbon fuels included gasoline, heptane, diesel, crude oil and ethanol. “When Trelleborg fire suppression spheres were applied at the incipient stage of a heptane/gasoline fire it very quickly and easily extinguished the eight-foot tank fire with the fire suppression spheres alone,” Kelly said. “In another test, we left it overnight to see if we could build up any flammable vapors. We came back the next day with torches and we couldn’t relight it.”  This vapor suppression performance was consistent with all of the fuels we tested including gasoline and ethanol where a three inch layer of fire suppression spheres would effectively suppress vapors indefinitely and ignition would not occur.  Long-term durability tests are currently underway and preliminary data suggests that the spheres show no failures in gasoline for one year.

In contrast standard water based foam requires repeated applications to maintain a vapor-suppression foam blanket, he said.

Each fire suppression sphere bears a special coating that provides high-heat resistance, oleo phobic properties to repel hydrocarbons and anti-static properties to mitigate static during movement or application. Fire suppression spheres are a development of Trelleborg’s advanced composite materials technology as used by NASA, the military, advanced aircraft design and deep-sea submersibles.

“We‘re materials experts,” Kelly said. “We put material on the space shuttle and on the Alvin, a three-man research submarine developed by the Woods Hole Oceanographic Institution. So we took our knowledge of these high tech applications and put it into vapor suppression and fire fighting.”

The oleo phobic repels hydrocarbons that might otherwise cling to the surface, Kelly said. The spherical shape and specific gravity of the spheres allows them to spread better and in layers, providing improved blockage of vapor paths.

“When you put the spheres on a hydrocarbon or a liquid, they tend to quickly run to the open spaces and fill any gaps or voids,” Kelly said. “The spheres travel around evenly. They don’t cluster together and get caught in spaces. They actually flow across the top of the fluids.”

In its purest form, fire suppression spheres are applied by means of permanently installed sacks or containers suspended inside the cone roof portion of a storage tank that release the contents upon sufficient heat, Kelly said.

“The sack has a heat fuse,” he said. “When the fuse reaches a certain temperature, it would open the sack and release the contents across the surface of the hydrocarbon.”

Field testing shows that when fire suppression spheres were applied from a suspended container at the incipient stage of a gasoline/heptane fire it will quickly extinguish it.  The fire was extinguished so quickly that approximately 95 percent of the spheres were not affected by the heat and could have been recycled for re-used.

Using fire suppression spheres as an additive to traditional fire foam is in an experimental stage but it shows great potential as the composite spheres complement traditional water based foam, Kelly said.

“During the tests in Spain it was called hybrid foam,” he said. “The foam is used as a carrier to help move the spheres, lubricate them and keep them cool.” This was particularly important with long pre-burns where the tanks’ walls conducted heat into the liquid.  Unfortunately, special nozzles have yet to be developed to educt the spheres into the foam stream, Kelly said. 

The boil over testing shows great promise and deserves more validation tests but the initial small scale testing in Spain demonstrated that using spheres led to a significant increase in time to boil over. A baseline test was run with boil over occurring approximately 25 minutes on the reference test with no spheres.  The time to boil over increased to approximately 90 minutes with just two inches of fire suppression spheres applied.

One unique aspect of the fire suppression spheres is that fluorochemicals are involved that might get into the environment.  Preliminary testing suggests that if the fire suppression spheres are not damaged they may be cleaned and recycled for re-use. 

“The material itself is worked out and is where we want it to be,” he said. “Now we are developing some of the application techniques and methods.”

One solution to the application problem may be sub-surface injection, Kelly said.

“We have not tested any sub-surface applications yet, but the spheres are very buoyant,” he said. “If it were injected sub-surface it would make its way to the top very rapidly and form a blanket.” This could be better in areas where lightning ignited vapor fires in fuel storage tanks may cause the roof to eject, taking the roof dispenser with it.

Testing in Spain also showed that fire suppression spheres, used in pure form or as a foam additive, was also effective against fires involving polar solvents such as ethanol.

“With alcohol resistant foam, you have to bounce off the back of the tank and let it hit the ethanol surface gently to form a blanket,” Kelly said. “Testing with AFFF foam on polar based fuel ethanol was predictably not successful until a thin layer of spheres was applied at which point it became successful. The composite spheres acted as a raft. When you hit that raft with standard fire training AFFF foam, which is very weak and entirely not suitable for ethanol, we were able to very quickly control and extinguish the ethanol fire.”

A three-inch layer of fire suppression spheres alone or used with a one-inch layer of dilute AFFF proved effective against an ethanol fire, testing shows.

Because fire suppression spheres take a radically different approach, marketing the product will present special challenges, Kelly said.

“We’re working on regulatory standards,” he said. “There are none for this type of product right now. We’re working on getting the standards written because it is so different from a traditional water based fire fighting foam.”

Trelleborg is soliciting advice from all corners of the fire fighting community as to how best to market its new product, Kelly said.

“We’re coming to the table saying ‘Listen, we’re experts in materials and you guys are experts in fire fighting,’” he said. “’Tell us what you think about this material.’ We’re not trying to say, ‘This is the latest and greatest – you have to use it.’ Tell us what you think we need to do to make you guy’s happy.’”

Trelleborg fire suppression and vapor suppression spheres have US and international patents pending.

 
 

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