Pre-Fire Plan, Training Essential For Handling Bulk Oil Storage Fires

Pre-Fire Plan, Training Essential For Handling Bulk Oil Storage Fires

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Petroleum products, particularly flammable liquids and gases, are an integral. part of our everyday lives. However, when large quantities are unintentionally released from their containment systems, they can present enormous problems for the fire department. When these incidents involve burning flammable liquid storage tanks, they may burn for days, easily overtaxing the capabilities of local resources.

Bulk storage facilities may be found anywhere, even in the smallest towns. Despite this, however, experience has shown a very low rate of fire incidence. In a 1979 survey of 11 major oil companies, the American Petroleum Institute (API) reported a total of 37 fires involving 47 storage tanks. It is obvious that very few people have direct experience with tank fire fighting.

In light of this inexperience, it is essential that fire departments adopt a pre-fire plan, with proper training at regular intervals, to effectively handle both leaks and fires in storage tanks. Obviously, the type and level of fire protection will vary according to the nature of the facility, its size and its complexity.

In most bulk storage facilities, large quantities of hydrocarbon products move through pipelines, storage tanks and loading racks—presenting a great potential for leaks and spills.

In many instances, these emergencies may be handled internally through the facility fire brigade. When an emergency does require the assistance of the fire department, responding personnel must recognize that they may not be familiar with the most effective methods of handling the incident. Consequently, the need exists for joint public safety and industry cooperation to develop well-defined plans for controlling emergencies at these facilities.

Fire control agents

When considering the primary fire control agents to be used during a bulk flammable liquid emergency, three questions should be addressed by the incident commander:

1. What type of agent is needed, and how much? Through pre-fire planning, the incident commander should have some assessment of his needs.
2. How much is available? Again, an inventory of available resources should illustrate where deficiencies exist. In most cases, the foam supplies on-site to handle a major incident at a bulk storage facility will be inadequate. In those areas where several major petroleum facilities exist, a foam mutual-aid network may be in place. In addition, many of the major foam companies have 24-hour emergency hot lines. The incident commander must recognize, however, that it takes time to get these supplementary extinguishing agents to the scene, and he should plan accordingly.
3. How will the agent be moved? If water supplies are inadequate, tanker shuttles or large-diameter hose relays may be necessary. Likewise, recognize that even if you have the capability to acquire large quantities of foams, you must also have the ability to apply the foam with enough eductors and nozzles of sufficient size.

—Courtesy of American Petroleum Photographic and Film Service.

Water can be used

Water, the almost-universal fire extinguishing agent, is useful around petroleum fires also. Serving as a cooling, quenching, smothering, emulsifying, diluting and displacing agent, water has the greatest heat-absorbing quality of any common material and usually is the most plentiful. It is used for cooling equipment, structures and tank shells that are exposed to a fire, thus preventing or reducing heat damage as well as the internal pressure of closed containers.

When used as a coarse spray, water can sweep pools of burning fluid out from under elevated tanks. Extinguishment will then result if the fuel surface can be cooled to below the vapor-producing temperature. When used on liquid hydrocarbon fuels having a flash point above 100°F, water can also be effective if applied in the form of a fog pattern. Below 100° F, water can ‘be used for control but will not extinguish the fire.

Water spray, when applied lightly to burning heavy viscous liquids with flash points above 200°F, is also very effective. By producing a layer of froth on the hot surface, the water will act like a foam and smother the fire. An example would be a hot asphalt tank fire.

When dealing with water-soluble flammable liquids, such as alcohols, dilution may be effective in some instances. Recognize, however, that the percentage of dilution necessary to effect extinguishment will vary with the product.

Frequently, water can be used as a displacement medium for handling leak conditions. Because liquid hydrocarbons are lighter than water and float on its surface, water can be injected in a container until the product line is raised above the leak and only water is escaping. Similarly, water can be used to displace the product in leaking liquid hydrocarbon lines. (Water pressure must be greater than product pressure.) However, these procedures cannot be used to displace liquefied propane gas or liquefied natural gas from a leaking pipeline, because the product temperature is below 32°F.

When dealing with spill and leak conditions involving hydrocarbon gases and liquids, water spray can also be effective for dispersing vapor clouds and gases. Likewise, it may also be used to protect operating personnel and fire fighters from radiant heat of flame contact.

Foam

Fire fighting foams are an aggregate of air-filled bubbles that will float on the surface of a flammable liquid. These foams are commonly made by mixing air with a water/foam concentrate solution to form a final aerated foam blanket. By preventing the formation of combustible mixtures of vapor and air, foam can prohibit the ignition of flammable liquid spills. Likewise, foams can extinguish burning fuels by forming a cohesive, floating foam blanket which smothers and cools the fuel. Foams are particularly suited for extinguishing flat, two-dimensional flammable liquid fires that involve spills or storage tanks where the foam can form a vapor-sealing barrier.

A ruptured fuel tank or line is a realistic scenario for any bulk storage facility. With fire involved, the foam will only be effective on pools of fuel that form flat surfaces. Final extinguishment can be completed by using dry chemicals, by shutting off the source of fuel that is feeding the fire or possibly by water spray (depending on the product’s flash point).

When attempting to control tank fires or liquid fires in depth, continuous foam application at the proper rate is critical. Unless the required rate of foam is applied and maintained on the surface until a cohesive foam blanket is established, the fire will not be extinguished.

In this scenario, the foams can be applied through portable devices such as foam towers, nozzles and foam cannons, or through fixed devices such as foam chambers and subsurface injection systems. One point of concern: when applying foams by hand lines or monitors over the rim of a tank, wind and thermal drafts may carry much of it away. As specified in NFPA 11, “Foam Extinguishing Systems,” the foam must be applied at a higher rate to replace this loss. Likewise, water lines applied in conjunction with the foams will simply break down the foam and wash the blanket away.

Numerous types of foam concentrates are available for use in fighting petroleum fires. These include protein and fluoroprotein foams, aqueous filmforming foams (AFFF) and high-expansion foams.

Dry chemicals

Dry chemicals are finely divided powders which inhibit the chemical chain reaction of the combustion process. Recognized for their unusual efficiency in extinguishing fires involving flammable liquids, they can be used alone or in conjunction with certain fire fighting foams. For example, potassium bicarbonate and AFFF are often found in twin-agent applications.

Dry chemicals are very effective on small spill fires and on fires from a leak. If there is a risk of reignition from embers or hot surfaces, the ignition sources should be cooled with water and secured with foam or the fuel source shut down before attempting extinguishment.

As in any fire fighting operation, the first action taken by the incident commander is the size-up process. If a plan has been prepared for an incident at the facility, many of the questions may already be answered. In addition to the usual factors addressed—time of day and week, weather, rescue requirements, and personnel and equipment resources—the incident commander must evaluate several other factors specifically related to petroleum tank fires. These include:

• Product involved and its physical and chemical properties.
• Type of tank involved and the condition of the tank shell and roof.
• Location of the fire in the tank, on the ground or both.
• Status of the tank and dike valves.
• Need for cooling exposed tanks and operating equipment.
• Type and status of any fixed extinguishing system.

Let’s look at each point individually.

Liquid fuels classified

Flammable liquid fuels are classified into flammable and combustible liquids depending on their flash points. Flammable liquid fuels have flash points below 100°F and can be ignited by ignition sources great distances from the spill area. Combustible liquids, such as kerosine, have flash points which range from 100 to 200°F, and usually will not give off vapors at normal temperatures. Combustible liquids are usually ignited by ignition sources close to the spill.

Flammable liquid fuels can be further separated into polar (water soluble) and non-polar (hydrocarbon liquids). This is an important consideration because it determines the type of foam applicable. Hydrocarbon fuels will not mix with water but can be extinguished with the standard foams such as AFFF, protein, and fluoroprotein. Polar solvents, such as alcohols and ketones, will mix with water and require special alcohol-resistant foams for extinguishment.

Types of tanks

Vertical flammable liquid storage tanks are usually one of three types of construction:

1. Cone or fixed roof, which has a Weak roof-to-shell joint.
2. Open top floating roofs (both cone and open floaters ae designed in accordance with API Standard 650).
3. Covered floating roofs, which consist of a fixed roof with an internal floating deck or pan.

It is essential that the incident commander determine the type of tank involved in order to calculate the foam and water requirements. Knowledge of the surface area will also be critical.

To handle internal explosions within the tank, the fixed roof tank with the weak roof-to-shell joint is designed to separate or blow off. This will result in a fire involving the entire flammable liquid surface. However, if the force of the explosion does not blow off the roof completely, there may only be a partial separation at the roof-to-shell joint. Although burning may be limited in this instance, extinguishment may be difficult due to an inability to apply agent through separation.

While vertical tanks will usually fail at the roof-to-shell joint, incidents have occurred where failure has taken place at the bottom seam. This will cause the tank to rocket out of the area, creating a severe flash fire followed by a large ground fire.

Open top floating roofs and covered roof floating tanks usually contain low flash point liquids and crude oils. Consisting of a ring, either fabric or a tube, between the tank shell and floating roof, these tanks have a very good fire record. Since the roof is floating on top of the product, the only place the product contacts air is at the seal. This is where the fires originate. They can involve either the entire tank circumference, or portions of it, and can be extinguished with foam hand lines and/or portable dry chemical extinguishers. Caution must be taken to prevent sinking a floating roof with excess water application. If the roof does sink, open floaters can be treated as cone roof tank fires.

Secure the flow

Fires may involve either the tank, the surrounding gound and dike area, or both. Tactics should initially be directed towards securing ground and dike fires, then attacking the tank fires sequentially. If ground and dike fires are not extinguished first they can reignite the tanks. This procedure will also be more favorable in light of the resources available. The tank sequence will be affected by the exposures, amount of product in the tanks, fire severity in each tank and the available foam resources.

The incident commander should determine the status of all involved tank and dike valves as soon as possible. If the tank valves are damaged by the fire, it may be impossible to stop the fuel flow. In some instances, the contents of a tank may be transferred to another tank to limit the amount of fuel flow from the damaged valve.

If dike valves remain closed, water may back up within the diked area and eventually overflow. The status of all dike valves, as well as any pumps which may be used to carry the water away, should be determined from the facility manager. In addition, determine the power source of the pumps, the effects of a power outage on your operation and potential supplemental power sources.

Critical areas

Certain tank areas and equipment are particularly susceptible to rapid damage from flame contact. These include:

• Uninsulated tank supports
• Exposed tank shell area above liquid levels (vapor spaces)
• Vents, pressure controllers, valving and gaging equipment
• Foam chambers, foam lines and other piping with no liquid flowing through them.

In order to prevent failure of this equipment, cooling water streams should be used, applied from maximum hose stream reach to ensure minimum exposure to fire fighters. Wind direction should be used to advantage. Fog lines and barriers may have to be used for protecting crews setting up hose steam appliances. Once the lines are in operation, they should be left unmanned. Security of all personnel must be the primary concern.

Depending on the tank spacing arrangments and wind conditions, cooling of exposed tanks is usually not necessary unless there is direct flame contact or radiant heat sufficient to scorch the paint. If there is any doubt, apply water from a hose stream and see if steam is produced. If the metal steams, cooling water should be applied until the steaming stops.

When tanks require cooling, the water streams should be allowed to run on the sides and roof for best results. The only exception to this are floating roof tanks, where water applied may actually sink the roof. In this case, water should only be applied to the sides.

Using water unnecessarily to protect exposures can deplete the volume and pressure of the water supply, and overtax sewers and drainage ditches. Should a valve or pipeline fail, it could result in flammable liquid floating on top of the water and spreading throughout the facility. In addition, there is the potential of floating empty or near empty tanks from their foundations. All of these factors should be considered during pre-fire planning.

Many tanks and bulk storage facilities are protected by fixed fire extinguishing systems. These include foam chambers, fixed foam monitors, and subsurface injection systems. The incident commander should know through his prefire planning if such systems are in place and should protect all foam chambers and foam lines with cooling streams to keep them intact for later use.

Situations may arise where it may be impractical to fight tank fires for a variety of reasons. In some instances, the cost of extinguishment could exceed the salvage value of the tank and its contents. Likewise, the fire department may not possess sufficient foam, water or foam producing equipment. Conditions may favor letting a fire bum under control, providing there is little chance the fire will spread and that adjoining exposures are protected.

Portions of this article were taken from American Petroleum Institute publications prepared by the Committee on Safety and Fire Protection.