Why we extinguish more tank fires today
Volume 24, No. 1
The refining industry is extinguishing a much higher percentage of large petroleum storage tank fires than we ever had, even though the tank sizes have grown to absolutely giant sizes.? Why are we much better at extinguishing these tanks? If you are not using portable monitors with large gpm self educting foam nozzles on your tank fires you are probably not having this success.
How has the industry handled tank fires in the past.? In the 1950's and 60's most tanks over 60 ft in diameter had topside fixed foam systems. These fixed systems had a foam concentrate tank and a proportioner in a building in the tank farm called the foam house. The foam house added the foam concentrate to the water coming from the plant fire protection water system at the correct percentage according to the foam manufacturer, then normally six percent. The mixed foam and water was and still is called Foam Solution.
The foam, at that time was a protein based mechanical type foam. The name protein is based on the fact that it was made from animal protein, mainly animal hoofs and horns. Because of the protein content it had a short life span and if prematurely mixed with water in a fixed system the foam would deteriorate and not work. So all protein foam had to be sampled and tested annually, this tradition is still done today even though our modern synthetic foams have an almost endless life expectance.
The foam solution was piped from a central foam house directly to each of the storage tanks in the tank farm. If there was 100 tanks that meant there was 100 sets of piping in the tank farm, literally going everywhere.
Once the delivery pipe got to the tank it had to be piped to the top of the liquid surface so there was a vertical pipe going up the side of the tank to a device called a foam chamber which expanded the solution with air then discharged the expanded bubbles of Foam into the tank. The air was added making the foam to get the foam solution to float on the burning surface, choking the fire.?
Because this mixing must be done by the equipment design or by a mechanical action we call them mechanical foams.? Even today all foam solutions must be expanded with air so they will float.? With the mechanical protein foams the volume of air was large enough to expand the foam solution about 8 to 10 times.? The current non protein foams usually need much less expansion, typically 3 to 4 times.
This type of foam system was and still is called a Fixed Foam System.? It had everything permanently piped up and ready to go, but there would be miles of piping that had to be maintained every year so they are very expensive systems to install and maintain.
During the 1960's another fixed system called the semi-fixed foam system was born when the fire truck manufactures designed a simple foam proportioning system that could be added to the fire trucks.? So almost over night all of the industrial fire trucks started having these Balanced Pressure Proportioner and a Foam Tank on each truck.?
Now that the foam house was on a mobile fire truck all of the piping could be eliminated except for the pipe going from the dike wall to the foam chamber.? This was the typical tank fire fighting methodology used until the 1980s.
The size of the hazard has changed because the size of the tanks suddenly started exploding.? In the 50's and 60's the largest tank was about 125 feet in diameter.? In the early 1970's engineers started building larger and larger tanks. These tanks grew to about 250 feet very fast and then in the 1980s they kept getting bigger until we got the 300 and even ome 400 feet in diameter tanks.
Fixed foam systems will not work on these larger tanks.? The problem is the fact that protein foam will not spread horizontally over a burning fuel over 80 feet.? This is commonly excepted and even explained in older versions of the Bible of foam system manual, the NFPA Pamphlet 11, Low Expansion Foam Systems.? So if the foam will not spread over 80 feet from the foam chamber how can it get to the middle of a tank over 200 feet in diameter.?
How did we ever put out a tank fire over 200 feet in diameter with a fixed system if this is true?? Well we have never extinguished a tank that big with a fixed system.?
Sure there are some foam manufactures and their consultants that say they have, but when you look at the results of these losses there is never any reasonable recovery of product and the tanks are a total loss.? So if they did not save any value how can anyone call it a successful extinguishment?
This means even today with the best foam available it is impossible to extinguish a tank larger than 180 feet in diameter with a fixed system.
How are these larger tanks extinguished today? They have been successfully extinguished using a system of Large GPM portable monitor nozzles and large diameter hose.? One example was the 290 foot gasoline tank at the Orion Refinery in Louisiana, USA on June 7, 2001.? It was not done with a fixed foam system.?
The new methodology of extinguishing these large tanks was born when Mr. Les Williams received a patent for a Self Educting Foam Fog nozzle in 1987.?
This invention eliminated the need for the foam proportioning system, because the nozzle sucks the foam in itself. The foam is mixed with air or expanded as it sprays through the air to the fire.? Modern foams use only a 4 to 5 expansion ratio.?
Williams' nozzle design and the latter manufacturing of larger gpm portable monitor nozzles made it possible to deliver enough foam to the center of the larger tanks like at Orion Refining.? Because the foam is sprayed into the tank with a forward velocity it can spread over the full surface area unlike the fixed system foam chamber which delivers the foam softly to the liquid surface with no forward velocity other than gravity.?
Les and his son Dwight continued to develop the large gpm portable trailer mounted nozzles fire fighting procedure that is so successful today. Les died in 1993 but Dwights company now holds many patents and is constantly coming up with different ideas to fight large tank fires.? His company is trying these new methods on real tank fires because they sell the service of extinguishing real tank fires all over the world.
NEW METHOD THAT WORKS
With this new portable self educting nozzle being scaled up to 14,000 gpm and using large diameter hose (six to 12 inch) to move the immense amount of water needed to extinguish the fires.
Any one that is seriously planning to extinguish a large tank must do it with portable large gpm self educting monitor nozzles, and large diameter hose usually sixto 7.25 inches in diameter with six inch Storz fittings. If the plant fire protection water system or the piping is not large enough, large portable pumps should be used to supply the water from ponds, rivers, or lakes.
The NFPA 11 pamphlet recommends a minimum application rate of .16 gpm/ft2 for tanks up to 60 feet. NFPA 11 does not address portable equipment for tanks over 60 feet in diameter.? The application rates used by the best practices guidelines have the following application rates on the larger tanks.
WHY DOES IT WORK SO WELL
The portable large gpm monitor attack works because of the following factors:
- Less equipment, the nozzle has the foam proportioner built in,
- Higher flow rates, portable monitors nozzles now made big enough to attack a jumbo tank,
- With much longer reach of the foam stream, the larger nozzle flows with much longer effective reach,
- Better foams that have great knock down ability, and are thinner flowing over a bigger area,
- Larger hose, hose allows the huge amounts of water to be moved to the fire with less friction loss,
- Large capacity super hydrants, with from three to six inch individual gated outlets with Storz fittings,
- Contract support services and fast foam delivery for contractors like Williams Fire & Hazard Control.
If you have large tanks and do not have a good preplan for this equipment you are not protecting your assets to the extent that todays high values respect.