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Monday
Jan172011

TFE 1

Damage Assessment

 

     This weeks post will discuss section 12-2.1 through 12-2.1.2 determining the extent of damage at a tank farm incident. It will be highly un-likely if you do not work at a tank farm to become familiar with the loading and off-loading procedure of tanks. Likewise, the transfer product lines to both loading racks from tanks, as well as production lines to storage tanks may be unclear at a Bulk Storage Incident. This is why early contact with plant emergency supervisors is so critical. The products stored reach their “fail-safe” ignition or explosive point in minutes. In all tank fire incidents, pre-fire planning has shown to improve extinguishment, life safety, and minimize property damage. Early deployment of Haz-Mat and Firefighting equipment is paramount. Once a tactic is decided, discharge of the chosen suppressant agent must begin as soon as possible.

     The responding Haz-Mat “Technician” can be more useful when involved with all pre-fire planning and Training at the respective Tank Farm in his jurisdiction. By being able to understand the normal flow of product into and out of the facility, you will have intimate knowledge of how the Farm operates in normal working mode. This concept not only prepares the “Technician” for the response, but is a part of his operational duties as a “FLBSS” {Flammable Liquid Bulk Storage Specialist}. The Haz-Mat responder can now make an early assessment of damage while responding to the scene by observance of the tank farm area involved in fire. This process of familiarity affords assessment before you arrive on-site. Possibilities of aggressive attack, defensive water volumes, or non-intervention, can all begin flowing through your thought process.

     Tank shape can determine many answers for the FLBSS. With this information you can determine volume, product type, volatility, and exposure dangers to adjacent tanks. There are four {4} basic tank shapes the “FLBSS” should be intimately familiar with involving low pressure liquids. They are; 1] a cone roof tank, 2] the open [external] floating roof tank, 3] the open floating roof tank with geodesic external dome and, 4] the covered [internal] floating roof tank. The FLBSS must be able to identify the differences in type and contents to make an accurate assessment of the hazards.

     The true cone roof tank, consists of a tank covered with a conical shaped roof affixed to the tank walls according to API 650 {American Petroleum Institute} must have roof to shell joints weaker than wall to base joints. Older tanks were originally constructed with wooden roofs that were prone to lightening strikes. Primarily containing flammable, combustible, and corrosive liquids, a weakened roof joint could explode away from the tank, confining the burning product inside the tank walls. Three basic means of extinguishment exist for these tanks, 1] Foam chambers either mounted or portable, 2] aerial towers or ground monitor Foam streams and 3]subsurface injection by high back-pressure Foam makers. Higher flash point fuels, above 100 F are harder to ignite and easier to extinguish, so as a rule, older tanks were not required to have fixed Foam systems. Picture 1 shows an example of a cone roof system without weak roof seams. This tank failed at its bottom seam, rocketing 60 meters with an ensuing large ground fire. As tank safety improved with time, these systems are seldom seen in widespread use.

     The open {external} floating roof is most commonly seen in storage tanks containing flammable and combustible liquids. These tanks are equipped with access ladders, fixed Foam systems, and no internal vapor space. Here, the roof floats on top of the product, eliminating an explosive atmosphere between the roof and fuel surface. In an extreme event these roofs can sink, but the most common fire involves the seal interface between the roof edge and tank wall. These types of fires are commonly extinguished by operators with Dry Chemical extinguishers or “catenary” Foam systems specific to the seal area.

     The same style tank with an added geodesic dome usually stores flammable liquids. This is essentially the same as above, except that the dome can perform functions ranging from weather protection to solar panel induction. If a geodesic dome has been destroyed, always check that the roof rain drains are open and operating. During a seal fire, access may be restricted for firefighting operations on the exterior of this type of roof.

     The covered floating roof tank stores flammables and combustibles, combining a floating roof inside a vented conical protective outer roof. This roof has venting capabilities allowing normal pressure increases to vent through openings near the top of the tank wall. Modern versions may have one vent at the apex of the cone. This type of intact seal fire connecting the roof edge and tank wall can be very difficult to access. These fires are usually extinguished with fixed systems discharging between the tank wall and seal contact area.

     Future posts will examine every aspect of firefighting operations and Hazardous Materials Spills in each of these various tanks.

                                                Haz Mat Mike

 



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