Types of storage tanks and flammable and combustible liquid stored in them, their fire protection systems, and brief servicing in case of spill
The devastating and costly experiences involving fire and flammable and combustible liquids have led to formulations of better guidelines and storage facilities for handling such liquids.
Practically, protecting flammable and combustible storage tanks from fire involves “the use of fixed or semi-fixed foam fire protection system” (NFPA 23).
Systems with proper installation and maintenance tend to be reliable. The foam is useful in “preventing, controlling, or directing extinguishment of any combustible or flammable liquid fire within the tank” (NFPA 27).
The fixed system refers to an installation system running from the main foam location through permanent systems to the hazard under protection. This system is complete and has permanent installation. On the other hand, a semi-fixed system installation has fixed discharge systems. It links with pipes, which end in a safe location from the hazard.
Open Top Floating Roof Storage Tank
This storage tank is like cone roof tank. It does not have a fixed roof. The “pontoon roof floats above the flammable or combustible liquid” (OSHA 50). There is a rim that seals “the space and the shell or side wall of the tank” (OSHA 50).
Cone Roof Storage Tank
This storage tank has a fixed cone-shaped roof. It also has vertical sides. This tank meets API standards. The tank’s design allows the roof to “blow off and leave the tank shell intact when internal explosion occurs” (OSHA 52). Thus, the tank can retain the liquid as the resulting fire will only burn the top of the exposed content.
Internal Floating Roof/Covered Floating Roof Storage Tank
This type of storage tank has both the “floating roof tank and cone-shaped roof” (OSHA 53). The internal floating roof lies directly on the tank’s liquid content. It has open vents at the sides. The internal floating roof can be “pontoon type or steel double deck” (OSHA 53). The internal floating roof may also have a sealed design area protection.
There are also flammable and combustible liquids stored in horizontal style tanks. These are underground and aboveground tanks.
These tanks have steel construction and meet specifications of the National Fire Protection Association (NFPA) and the Uniform Fire Code of the International Fire Code Institute (IFCI). Still, underground tanks may also have different materials from steel.
However, these materials master meet standards of steel or conform to design standards for storage of flammable and combustible liquids.
The operating pressure of the tank cannot go beyond “the design pressure of the tank” (NFPA 343). These tanks have systems that release excessive internal pressure that may result from exposure to fires. Such relief systems must meet the standards in the NFPA provisions.
These tanks also have dikes and drainage systems as required in the NFPA guidelines in order to prevent any accidental discharge of flammable and combustible contents. This is usually to protect nearby facilities and waterways.
Underground tanks must meet NFPA standards and other provisions. These tanks must undergo thorough tests before installation. Underground tanks must also meet corrosion standards as different states require (NFPA 343).
Types of Flammable and Combustible Liquids stored in the tanks
The NFPA 30 Code provides minimum standards for flammable and combustible liquids storage tanks, storage, transportation, and handling. In addition, it also provides various classifications of flammable and combustible liquids.
This classification uses boiling point and flash point of these liquids as set by “American Petroleum Institute (API) or American Society for Testing and Materials methods” (NFPA 467).
Flashpoint refers to a “minimum temperature at which a liquid gives off vapor within a test vessel in sufficient concentration to form an ignitable mixture with air near the surface of the liquid” (NFPA 467). A liquid, in this case, refers to any material that has more than “300 fluidity of penetration asphalt” (NFPA 467).
We can apply two common methods to classify flammable and combustible liquids. These are non water miscible (hydrocarbon) and water miscible (polar solvent) methods.
Hydrocarbon liquids include jet fuels, gasoline, and crude oil among others. On the other hand, polar solvent liquids consist of esters, alcohols, and ketones among others (OSHA 53).
|Classification of Flammable Liquids||Flash Point||Boiling Point|
|Class IA||Below 73 0F or 22.8 0C||Below 100 0F or 37.8 0C|
|Class IB||Below 73 0F or 22.8 0C||Below 100 0F or 37.8 0C|
|Class IC||At or above 73 0F||Below 100 0F or 37.8 0C|
Source: Flammable and Combustible Liquids Code, 1969 edition.
|Classification of Combustible Liquids||Flash Point|
|Class II||At or above 100 0F (37.8 0C) and below 140 0F (60 0C)|
|Class IIIA||At or above 140 0F (60 0C) and below 200 0F (93.3 0C)|
|Class IIIB||At or above 200 0F (93.3 0C)|
Source: Flammable and Combustible Liquids Code, 1969 edition.
Source: 29 CFR 1910.106
Fire protection systems of flammable and combustible liquid tanks
The first step to fire protection requires the use of approved tanks for storage and holding of flammable and combustible liquids. Thus, storage tanks for flammable and combustible liquids must meet NFPA 30 Code and the OSHA standards.
Storage tanks have steel walls approved for storing flammable or combustible liquids. However, different materials for these tanks (underground) must meet standards of steel as well as required design.
Manufacturers and operators of these tanks must ensure that normal “operating pressure of the tank cannot go beyond the design pressure” (OSHA 54). Atmospheric pressure tanks cannot substitute low pressure tanks.
During installation, engineers must ensure that the “spacing (shell-to-shell) of aboveground tanks must not be less than three feet” (OSHA 54). This is the distance between two tanks of flammable and combustible liquids.
The distance between two adjacent tanks is crucial during installation. This is necessary to facilitate firefighting in cases of fires. Thus, irregular arrangements or compact tanks need wider spacing between them for ease of accessibility.
The tanks must also have a distance of 20 feet between them if they are flammable or combustible liquid tanks and liquefied petroleum gas tanks. This distance depends on the pressure at which the tanks operate.
For instance, it will be different if the pressure of a flammable or combustible tank exceeds 2.5 psig, or in cases where the tank has emergency venting. Emergency venting allows the pressure to go beyond 2.5 psig.
There should be no accumulation of flammable or combustible liquids next to liquefied petroleum gas container by any means. The liquefied petroleum gas (LPG) container cannot share the same dike with flammable or combustible liquid tanks. The LPG container must be 20 feet away from a flammable or combustible liquid tank. In all, LPG can never be installed in diked areas.
Fire protection from storage tanks also accounts for atmospheric pressure. The designers must ensure that atmospheric storage tanks have adequate vents to eliminate developments of pressure or vacuum.
Pressure and vacuum can damage the “roof of a cone roof tank or can go beyond the tank’s design pressure” (OSHA 54). This may occur due to filling, emptying, and changes in atmospheric temperatures.
Normal vents must conform to three provisions. First, they must meet specifications of API 2000. Second, vents must also conform to other accepted provisions. Finally, vents must also be larger than or equal to withdrawal and filling pipes. The recommended vent diameter should not be less than 11/4 inch.
Storage tanks also have protection mechanisms that inhibit “overpressure which may originate from pumps discharging liquid into the tank” (NFPA 45). This is necessary because discharge pressure may surpass the design pressure of the tank.
Aboveground storage tanks have devices that relieve “excessive internal pressure, which may result from exposure to fires” (NFPA 45). Relief systems must also meet NFPA 30 set standards.
Storage tanks have drainage systems. Drainage systems cater for any accidental discharge and prevent flammable or combustible liquids from getting into waterways. As a result, there are dikes that retain flammable or combustible liquids around the tank. The size and volume of dike must also meet certain standards.
First, volume of the dike must be able to contain the amount of liquids that the tank can release at a given times when it has a full capacity. This method considers “the volume of the tank and height of the dike” (OSHA 54) in order to determine the capacity of the dike.
Second, tanks with fixed roofs, which have liquids with boil over tendencies, consider the volume of the largest tank that an enclosure serves so as to determine the carrying capacity of the dike if these tanks have full capacities. At the same time, this process must also consider capacities of “all tanks within an enclosure where the dike is” (OSHA 54).
Dikes must meet specified construction standards. This takes into account the location and weather factors such as flooding. There are also emergency procedures in case of flooding at the site. Overfill protection systems are above the ground as recommended under IFC and NFPA Codes.
The system also ensures that all sources of ignition are under control in accordance with the “OSHA standards and other applicable codes” (OSHA 51).
Sources of open flame are under strict restriction with visible signs of “NO SMOKING BY ORDER OF THE FIRE DEPARTMENT” as stipulated in the IFC 2003 standards (OSHA 57).
Installed electrical devices meet the standards of NFPA 30 current version, ICC Electrical Code, and National Electrical Code. Electrical pumps also have control mechanisms, which allow them only to function when the dispensing nozzle is out of its normal area or bracket.
The control uses a manual switch for activation. These control mechanisms stop nozzles once they are in the bracket, or not in normal positions of dispensing.
The storage tanks of Class I or II liquids also have mechanisms which minimize accumulation of static electricity during dispensing. This uses proper grounding and bounding systems.
The storage tanks also have corrosion control methods that meet OSHA requirements and other standards.
The storage tanks meet material specifications and quality recommended for piping, pipes, and valves.
All underground tanks have connections at the top. In addition, all vents terminate at the end as required under the OSHA standards.
Servicing flammable and combustible liquid tanks in case of a spill
The NFPA 329 sets standards and recommendations for handling all releases of flammable and combustible liquids, and gases (NFPA 45). The most important recommendation is to find the source of the spill, and then conduct a thorough cleanup and disposal.
All tanks storing Class I, II, or IIIA liquids must avoid cases of accidental spills so as to protect nearby property, facilities, and waterways. Storage tanks must also have remote impounding and impounding tanks with dikes. In some cases, storage tanks may require both remote impounding and diking, and a closed-top diking.
The NFPA Code and other applicable standards provide specifications on spill control and secondary containment. Storage tanks located outside and exposed to rainfall have design to contain spills from the single largest container.
At the same time, it must also have the capacity to hold “a volume of a 24-hour rainfall based on a 25-year storm” (NFPA 234). The system also has channels to drain accumulated water.
Controlling spills also requires maintenance and inspections of storage tanks regularly. Locations prone to flooding need constant “inspection and review of the emergency plan provisions” (NFPA 234). This is because floods may weaken foundations and other supporting structures. This also applies to areas prone to earthquakes.
Storage tanks maintenance and operating procedures must conform to set standards of approved codes. There should be a prompt cleanup of any spills and proper disposal.
The codes do not have any specific training requirements. However, the industry must ensure that it improves compliance through regular employees training on safety standards.
These trainings should focus on popular areas like handling, storing, and transferring flammable and combustible liquids. In addition, trainings should also include regular maintenance practices.
How to putout fire and control spillage using different methods
People operating storage tanks for storing flammable and combustible liquids must be familiar with the hazards and characteristics of such liquids. Spills can result into costly fires.
Therefore, before any fire occurs, the person responsible for the spill should act promptly and cleanup the area. This is because acts of carelessness during cleanup can cause injury, illness, spread of the liquid to the environment, fire and severe damages to property, or even claim lives.
It is important that people handling flammable and combustible liquids know essential steps in handling spills and controlling fires. Therefore, adequate training, supply of cleanup materials, and protective equipment must be available in the location.
Flammable and combustible liquids need cautious handling, storing, and transferring. However, the general rules to eliminate cases of fire from flammable and combustible liquids involve avoiding sources of open flames such as “smoking, avoiding static electricity, ensuring electrical gadgets are compliant, and preventing hazardous mixtures” (OSHA 53).
Eliminating cases of hazardous mixtures of flammable and combustible is necessary in preventing cases of explosions and fire. Therefore, it is necessary to label all containers used in storing flammable and combustible liquids. It is also important to keep distance between storage tanks and classes of different flammable and combustible liquids.
It is also fundamental to prohibit “smoking and other sources of open flames in areas with flammable and combustible liquids” (NFPA 473). This is the basic step to reducing cases of fire and explosions at such locations.
Therefore, people should not smoke, use matches, lighters, and other materials which may produce flames or sparks when dealing with flammable and combustible liquids. Location of signage must be visible for all people visiting the plant.
Location of fire extinguishers should be conspicuous for all employees for accessibility during a fire. Employees should be familiar with operating instructions of fire extinguishers. Fire extinguishers also need regular inspection and maintenance to ensure that they are functional.
According to OSHA, inspection of fire extinguishers should be at least once a year (OSHA 57). There should be a date of inspection and the next date of inspection clearly indicated on the extinguisher.
OSHA recommends that fire extinguishers should be placed facing up and regular inspection of hose for any blockage. Seals should not indicate any sign of tampering.
Employees must also learn how to face a fire with an extinguisher. The NFPA recommends that people should recall “PASS” when handling fires (NFPA 469). These are the steps to observe when extinguishing a fire.
They are pulling or pressing the lever or pin of the extinguisher, aiming at the base of the fire, squeezing the handle to release extinguishing agent, and sweeping from side to side until the fire goes out.
NFPA also indicates that it is dangerous to turn back on a fire. This is because the fire has the potential to flash up again. NFPA and OSHA warn that people should leave the facility in case of a large fire that they cannot handle with available facilities.
They must call the fire department immediately. This should be clearly indicated on the emergency plan in case of a fire. The fire department must provide training on dealing with fires in extreme cases.
Fire fighting remains a dangerous undertaking. It is necessary to invite a fire department to train workers on various methods of handling fires. At the same time, they should also tour the plant and provide recommendations as necessary. It is necessary to identify faulty areas and potential sources of fires.
Cases of poor services of fuel tanks that led to catastrophic disasters: what was wrong or poor service?
No fires are similar based on their causes and patterns. However, they have same destructive effects on the environment, property, and sometimes on lives of people. These are the cases of BP Texas City Refinery Explosion and the Buncefield fire of the UK in 2005.
BP Texas City Refinery Explosion
The CSB report indicates that BP failed to “implement all the safety recommendations about the blowdown drums before the explosion” (CSB 1). Initial reports had indicated that the company was familiar with the issue of blowdown drums.
Previously, Amoco proposed to replace blowdown drums that vented into the atmosphere. However, there were budget strains changes, and it did not make any changes. OSHA had also expressed its concerns about unsafe design of such pressure releasing system. BP ignored safety issues in order to cut costs.
Blowdown drums and stack operate by means of carrying “the mixed liquid, and or vapor hydrocarbons from venting relief and blowdown valves during unit upsets or following a unit shutdown” (CSB 5). Usually, remaining hydrocarbon vapors detach themselves from the liquid and rise to the top of the stack and escape to the atmosphere.
Heavy, hydrocarbon vapors condense and fall back to the bottom of the blowdown drum for subsequent collections. However, according to the report based on the industry provisions, this method of discharging vapor is hazardous. The codes and other acceptable standards recommended that such facilities should discharge their wastes directly to the sewer.
The company knew that the vapors, which passed through the blowdown drum, were highly inflammable liquid contents, and thus, any explosion could be highly risky. Further, blowdown drums were also sources of fire hazard.
The company heavily depended on the blowdown drum. However, it failed to implement any recommendations from various inspection reports.
Specifically, CSB report put it that the company “failed to replace the internal baffles, decommissioning the quench system, and adding more inlets, which possibly reduced its effectiveness” (CSB 32).
Earlier reports had indicated that the company should install flare systems or closed relief systems. These designs have abilities to reduce such risks considerably.
Many reports have indicated failure of the company to upgrade its systems to acceptable safety standards even after recommendations. Blowdown drum should not vent into the atmosphere due to their risks to the flammable and combustible liquid facilities and the surrounding environment.
The BP Texas City Refinery safety standards of 1977 noted as follows “the industry standards did not permit new blowdown stacks, and BP ought to have connected the blowdown drums to closed systems or flares when the operations of the company outgrew existing facilities, or when it made major modifications to the units” (CSB 67).
The company made changes to the blowdown drums in order to increase their carrying capacities. However, the company did not include any connection to a safe disposal system such as a flare as recommended.
In the year 2002, engineers from the company recommended that BP should connect relief valves to a flare for discharging wastes in order to conserve the environment. However, the company disregarded this recommendation in order to save costs on maintenance.
BP Texas City Refinery Explosion shows the importance of upgrading systems that handle flammable and combustible liquids. It is clear that the explosion resulted from poor and outdated blowdown drum, which could not meet increased activities at the refinery.
Thus, it is important for companies to build their storage facilities to meet acceptable standards in the codes and regulations of various states.
The Buncefield Fire 2005
The report showed that the explosion probably emanated from ignition of a vapor cloud suspected to have originated from a storage tank. This could have happened from overfill of unleaded petrol. However, the report cannot account for the violet blast that occurred at the facility.
The finding points to a failure of the shut down system that lock tank when it is full after delivery. It also focused on the composition of the liquid. This case resulted into a serious environmental concern due to its impacts on the groundwater.
The Buncefield Fire raised issues relating to three areas. This included “design and operation of storage sites, emergency response to incidents, and advice to planning authorities” (HSE 18).
From the design and operation point of view, the facility failed to contain fuel and water (firewater) used in firefighting at all levels. Thus, the facility failed in containment standards. The primary aim of a containment structure is to ensure that the liquid does not spread outside the vessel and dike area.
This indicates that future designs must consider building dikes and other methods of containing the liquid to prevent it from leaving the tank and forming flammable or combustible vapor. The report recommended bund and drains as means of providing secondary and tertiary containment strategies.
There was also a case of “overtopping”. This practice has the potential to produce dangerous and explosive mixtures from flammable and combustible liquids. The report also noted that the design of the tank could have also been a source of vapor formation.
There was also a problem with the location of the pump house. This is the main source of cooling water for the whole plant. The pump house was close to storage facilities and also downhill. The reported indicated that it could have been the source of earlier ignition.
The pump house acted as the source of firefighting for the facility. Its earlier loss left the site with no means to fight the fire. The Board noted that pump house could have exploded internally from the vapor that entered it after escaping the vessel. It posed a threat to fire pumps.
The Board noted that the response to the situation was “very impressive” (HSE 21). It has shown how effective emergency response works in case of a major incident.
It also showed the need to improve in responding to emergency incidents across the UK and other places. The Board noted that the facility, residential, and commercial development should not be near plants like Buncefield.
CSB. BP Texas City: Final Investigation Report. Texas: CSB, 2005. Print.
HSE. Buncefield Major Incident Investigation Board. London: Crown, 2006. Print.
NFPA. NFPA 30 Flammable and Combustible Liquids Code 2012 Edition. Quincy, MA: NFPA, 2012. Print.
OSHA. Regulatory Compliance Guide. Washington, DC: OSHA, 2002. Print.