HAZ-MAT EMERGENCIES INVOLVING INTERMODAL CONTAINERS
PART 2: INTERMODAL TANK CONTAINERS
BY GREGORY G. NOLL, C.S.P.
This article is designed to provide emergency response personnel with background information, general procedures, and response guidelines for operating at incidents involving intermodal containers. Part 1 dealt with intermodal freight containers; here, we are discussing tank containers.
The use of portable tank containers, also referred to as “tank containers” or “iso-tanks,” has increased greatly during the past decade. Factors contributing to their popularity include improved safety, portability, lower transportation costs, and the advantages of a multimodal transport system. Like cargo tank trucks and railroad tank cars, different types of intermodal tanks are built to many domestic and international standards. They are being used to transport a varied and diverse range of commodities, including an increasing number of hazardous materials. It is projected that by the year 2000, the total number of intermodal portable tank containers will exceed 90,000.
DESIGN AND CONSTRUCTION FEATURES
An intermodal portable tank usually consists of a single, noncompartmentalized vessel held within a sturdy, metal-supporting frame that allows the unit to be lifted by appropriately designed handling cranes. The framing allows securement of the portable tanks on both vessels and surface vehicles.
Key construction features include the following:
Tank container. The tank itself is generally built as a cylinder enclosed at the ends by ellipsoidal, hemispherical, or flanged and dished tank heads. Although rare, rectangular tanks and tube tanks may also be found. The portable tank is usually a single, noncompartmentalized vessel with a capacity that does not exceed 6,340 gallons (24,000 liters). Multicompartment intermodal tanks are rare; however, when found, each compartment is constructed as a separate tank. There are typically no internal baffles on intermodal portable tanks.
Tank containers may be equipped with various features, including the following:
–Linings to protect the tank from its contents. Linings can be rubber, glass, or other coverings applied to the inside of the tank after it is built.
–Refrigeration units. Most tanks with refrigeration units are not provided with their own power source; an external supply source is required. Depending on the mode of transportation, options may include a ship`s power system, a plug-in at a fixed facility, a chassis-mounted generator for highway use, a freight car generator, or a generator container.
–Heating units for handling very viscous products. Options include electrical or steam heating. Electrical heater coil units are commonly found where the product must be heated during transportation and may be installed on the interior or exterior of the tank container. They operate on 200-240 volt or 340-480 volt, three-phase electrical supply. Steam heating is provided by pumping steam through external heater coils on the lower half of the tank.
–Insulation. It moderates the effects of the ambient temperature on the contents. Insulating materials include polyurethane foam, polystyrene foam, mineral wool, and fiberglass. Insulation is usually three to four inches thick and is always covered with a jacket with flashing to make it weathertight. Jackets are made of metal, at least one millimeter thick or an equivalent thickness of plastic reinforced with glass or fiber. Remember that the tank is attached to the container framing; the insulation is not an integral part of the tank.
–Electrical controls. The electrical control box is mounted on the tank frame at the rear of the tank container (i.e., the end at which the discharge valve is located). The control box will contain fuses or circuit breakers, temperature controls, the main switch to isolate the tank container from the power supply, and a method of selecting the correct circuit for the available main power supply.
Materials of construction. Because of its strength and excellent properties in cold temperatures, more than 90 percent of intermodal tanks are constructed of stainless steel. The remainder are constructed of mild steel. Aluminum and magnesium alloy tanks may also be found, but they cannot be used in marine transportation.
Shell thickness is measured in terms of “equivalent thickness in mild steel” after forming. Shell thickness requirements can be summarized as follows:
If you see external rings on an intermodal tank, it is most likely a single-shell, stainless-steel tank. Most tanks are constructed to the pressure-vessel standards of the American Society of Mechanical Engineers (ASME). Welds are x-rayed; the welds on carbon steel tanks are post-weld, stress-relieved.
Size and supporting frame. The supporting frame of a tank container protects the tank and provides for stacking, lifting, and securing the container. It also supports the walkways and ladders.
The most common size supporting frame for tank containers is length: 20 feet, width: 8 feet, and height: 8 to 912 feet. Very few tank containers used within the United States are longer than 20 feet. An exception is the Sea-Land Company`s half-height tank containers, which have a length of 35 feet. However, 30-foot-long tanks may be found in other countries.
Two basic types of supporting frames can be found: the “box type,” which encloses the tank in a cage-like framework with continuous side rails, and the “beam type,” which uses frame structures only at the ends of the tank. The “beam type” relies on the inherent strength of the tank as a beam.
Portable tank containers are usually described in relation to the end of the tank fitted with the discharge valve, referred to as the “rear end of the tank.” The right and left sides are determined when facing the rear end.
Corner castings. Like freight containers, supporting frames for tank containers are built with corner fittings, commonly referred to as “corner castings.” They are used to secure the tank and lift it with standard container-handling equipment. Cast-iron corner castings are prohibited. In the event of an accident, the corner castings may be used for lifting or moving the tank, but only after consultation with the tank`s owner or manufacturer.
TANK CONTAINER MARKINGS
A number of markings on tank containers can be used to gain knowledge about the tank design and construction features. These markings include the following:
Reporting marks and number. Tank containers are registered with the International Container Bureau in France. They must be marked with reporting marks and a tank number. The initials indicate ownership of the tank; the tank number identifies the specific tank. These markings are generally found on the right-hand side of the tank (as you face it from either side) and on both ends (see below). They may be displayed on the tank itself or the tank frame.
Specification marking. The specification marking indicates the standards to which a portable tank was built. Tank containers must meet U.S. Department of Transportation (DOT) design, construction, and safety standards. These markings will be on both sides of the tank, generally near the tank`s reporting marks and number.
Examples of specification markings are:
* Spec. 51
DOT exemption marking. Exemptions from DOT regulations are sometimes authorized. In these cases, the outside of each package/container must be plainly and durably marked “DOT-E” followed by the exemption number assigned (e.g., DOT-E8623). On intermodal tanks, these markings must be in two-inch letters.
AAR-600 marking. For interchange purposes in rail transportation, intermodal tank containers should conform to the requirements of Section 600, “Specification for Acceptability of Tank Containers,” of the Association of American Railroads (AAR) Specifications for Tank Cars. Tanks meeting these requirements will display the “AAR 600” marking in two-inch letters on both sides near the tank`s reporting marks and number. The “AAR 600” marking indicates tanks that can be used for regulated materials; the “AAR-600NR” marking indicates tanks that cannot be used for regulated materials.
Country, size, and type markings. The country code (two or three letters) indicates the tank`s country of registry. The tank will display a size/type code (LR-2276 in the photo on page 62 bottom).
The four-digit size/type code follows the country code. The first two numbers jointly indicate the container`s length and height. The second pair of numbers is the type code, which indicates the pressure range of the tank.
Common Size Codes
20 = 20 feet (8 feet high)
22 = 20 feet (8 feet 6 inches high)
24 = 20 feet. (> 8 feet 6 inches high)
Common Type Codes–Maximum Allowable Working Pressure
70 = < 0.44 (6.4 psig) bar* test pressure
71 = 0.44 (6.4 psig) to 1.47 (21.3 psig) bar test pressure
72 = 1.47 (21.3 psig) to 2.94 (42.6 psig) bar test pressure
73 = spare
74 = < 1.47 (21.3 psig) bar test pressure
75 = 1.47 (21.3 psig) to 2.58 (37.4 psig) bar test pressure
76 = 2.58 (37.4 psig) to 2.94 (42.6 psig) bar test pressure
77 = 2.94 (42.6 psig) to 3.93 (57.0 psig) bar test pressure
78 = > 3.93 (57.0 psig) bar test pressure
79 = spare
* 1 bar = 14.5 psi
Dataplate. Additional technical, approval, and operational data can be found on the dataplate, which is permanently attached to the tank or frame.
A tube that contains the tank`s shipping documents or a material safety data sheet (MSDS) may also be found in proximity to the dataplate. Constructed of metal or plastic, these tubes are normally at or near the rear end in proximity to the discharge valve.
Tank and valve test dates. If installed, tank and safety valves must have a retest interval no greater than five years. Retest and test due dates must be marked or stenciled on the tank or dataplate.
Markings and placards. Tank containers containing regulated materials must be marked and placarded. The four-digit identification number must be displayed. For domestic shipments within the United States, DOT regulations require that the proper shipping name be printed in two-inch letters on two opposing sides of the container shell. On international shipments, foreign placards, in addition to those required by the United States, are sometimes found. European shipments may carry the ADR/RID markings.
Some specific situations of which responders should be aware regarding the placarding of international shipments are as follows:
–Tanks loaded with a regulated commodity must display the appropriate DOT placard to correspond with the classification of the commodity. In addition to the required DOT placard, any additional placard authorized by the International Maritime Dangerous Goods Code (IMDG) should be found [see 49 CFR 172.502(c)(1)].
–The required placard must meet the DOT placard design specifications. For example, an INFLAMMABLE placard would not be legal in lieu of a Flammable Liquid placard, even though they are identical in size, color, and intent.
GENERAL CLASSES OF TANK CONTAINERS
Tank containers are classified according to the specification of the portable tank and its fittings. The tank container class determines which products may be transported. The general classes of tank containers include nonpressurized, pressurized, and specialized. The Intermodal Tank Table found in 49 CFR Part 173 provides a list of hazardous materials approved by the DOT for transport in portable tank containers.
The three most widely used specification tank containers permitted to transport hazardous materials in North America are the IM-101, the IM-102, and the Spec. 51 containers. These portable tanks generally correspond to the design specifications set forth for international transportation by the International Maritime Organization (IMO) for the IMO Type 1, IMO Type 2, and IMO Type 5 tanks.
Nonpressure Tank Containers
Although classified as nonpressurized, these containers can have a working pressure up to 100 psig. Nonpressure tank containers comprise more than 90 percent of the total number of tank containers; the most common are the IM-101 and IM-102 portable tank containers. The only clue to distinguishing an IM-101 from an IM-102 container is to physically inspect the dataplate or container markings.
Nonpressure tank containers can transport both liquid and solid materials at maximum allowable working pressures (MAWP) of up to 100 psig. Tanks are tested to at least 1.5 times the MAWP.
IM-101 portable tanks (International IMO Type 1). These tanks are built to withstand MAWPs ranging from 25.4 psig (1.75 bar) to 100 psig (6.8 bar). DOT specifications for the design and construction of IM-101 tanks can be referenced in 49 CFR 178.270 and 178.271.1. An ASME certification or stamp is not required.
IM-101 tanks are used for transporting hazardous and nonhazardous materials, including toxins, corrosives, and flammables with flash points below 327F (07C). Capacities are normally in the range of 5,000 to 6,300 gallons.
IM-102 portable tanks (International IMO Type 2). These tanks are built to withstand lower MAWPs, ranging from 14.5 psig (1.0 bar) to 24.4 psig (1.75 bar). DOT specifications for the design and construction of IM-102 tanks can be referenced in 49 CFR 178.270 and 178.272. An ASME certification or stamp is not required.
IM-102 tanks transport materials such as whiskey, alcohols, some corrosives, pesticides, insecticides, resins, industrial solvents, and flammables with flash points ranging from 327F (07C) to 1407F (607C). These containers are also commonly used for the transport of nonregulated materials such as food-grade commodities. Capacities are normally in the range of 5,000 to 6,300 gallons.
–Dataplates. Each tank must have a corrosion-resistant dataplate permanently affixed to the portable tank in a location that is readily accessible for inspection. If the information is provided in metric, responders may have some initial difficulty with conversions. The following information is required:
U.S. DOT Specification Number (e.g., IM-101 or IM-102);
country of manufacture;
date of manufacture;
manufacturer`s serial number;
identification of USA/DOT approval agency and approval number;
maximum allowable working pressure–MAWP (psig or bar);
test pressure (psig or bar);
total measured water capacity at 687F (207C) in gallons or liters;
maximum allowable gross weight (lbs. or kg.);
equivalent minimum shell thickness in mild steel (inches or mm);
tank material and specification number;
metallurgical design temperature range (7F or 7C);
lining material, if applicable;
heating coil maximum allowable working pressure (psig or bar), if applicable; and
corrosion resistance (inches or mm), if applicable.
–Tank container fittings. The following fittings can be found on the IM-101 and IM-102 tank containers to make them both safe and functional. Although many of these fittings are similar to those found on a cargo tank truck, container fittings and threads are normally British Standard Pipe (BSP) or metric.
Access to top fittings is normally via a ladder and walkway installed on the container. Tank container ladders may be loose or weakened. During emergency situations, emergency responders should consider the use of portable ladders for access to the top of the container. Do not walk on the tank shell.
Tank container fittings include the following:
* Spillbox. On most nonpressure tanks, the top fittings are surrounded by a spillbox, which protects the shell of the tank from product spillage. Spilled materials, as well as rainwater in the spillbox, are drained away to the ground through one or more small open pipes.
* Manhole, cover, and dipstick. An 18- to 22-inch manway is located on top of the tank at the center. It is enclosed by a hinged or bolted lid fitted with six or eight large wing nuts. A replacement gasket is used with the manhole; neoprene (food quality) is standard. Other gasket materials may include Viton© and Teflon©.
A dipstick may be inside the manhole or lying within the spillbox. It is used in conjunction with a calibration chart, also known as a “strapping chart,” to measure the amount of product in the tank. Tanks must be loaded to at least 80 percent of capacity to avoid sloshing. For liquids, a minimum outage of two percent of the total capacity of the tank must be provided in rail transportation.
* Top-loading valves. Top-loading valves are attached to a removable eduction pipe (e.g., dip leg, dip tube, or siphon tube) running into the tank. They can range from 112 to four inches in diameter, although they are typically three-inch-diameter balls or butterfly valves with a four-bolt flange.
* Bottom outlet valves. They can range from 112 to four inches in diameter. When a tank container is intended to transport hazardous materials, two externally operated, bottom-outlet valves are required. Typical designs are for a three-inch internal foot valve, a three-inch external butterfly valve, and a three-inch BSP thread screw cap. They are connected in series with a replaceable gasket between them. Some containers may also have electrical sensor connections adjoining or as part of the bottom outlet valve to provide product identification and product overfill protection. This is similar to the sensor connection commonly found on gasoline tank trucks to prevent product overfills at loading racks.
Also required is a liquid-tight closure on the external valve. It may be a blind flange, a screw cap, or a cam-lock cap attached to the external valve. Blind flanges are required for international shipments. AAR 600-12 requires a positive lock on the external bottom valve to lock in the closed position.
Emergency response experience shows that most leaks occur at the blind flange as compared with the valve itself. Flange leaks can be easily controlled by tightening down on the flange bolts.
* Airline connection. An airline connection can be used for pressure unloading, vapor return, and blanketing the contents with an inert gas. It is normally a 112-inch line. In some instances, a 112-inch ball valve and pressure gauge may be found. This connection can be found on the tank`s top, normally within the spillbox.
* Thermometer. Some tanks have a built-in thermometer to measure the temperature of the lading. If a tank is equipped with an electrical or a steam-heating system, it will most likely be provided with a thermometer. The thermometer may be an immersion sensor or a surface, which is connected to a temperature gauge. Temperature gauges will usually read both in Fahrenheit and Centigrade.
Tank container safety devices. The following safety devices can be found on the IM-101 and IM-102 tank containers.
* Pressure/vacuum relief valves. They are generally found in pairs on nonpressure tank containers. Typically, two three-inch- spring-loaded devices are installed on top of the portable tank near the manway.
A combination pressure/vacuum relief device protects the tank from overpressure and a vacuum of more than 0.75 psig negative pressure. The valve will be marked to indicate its settings. In many cases, the relief valve will also have a rupture disk (i.e., burst disc) located between the safety relief valve spring and the commodity to protect the spring from the commodity.
This fitting may also have a gauge to determine if the disk is ruptured. The pressure gauge normally reads in both psi and bars; the gauge should always read zero.
Responders may find situations where the burst disc has failed but the relief valve has not actuated. Among some of the reasons for this may include container overfilling, product expansion due to ambient heating, and hydraulic surge effects.
* Emergency remote shutoff device. This emergency device can close the internal bottom outlet valve (foot valve) from a remote location. As one faces the discharge end of the tank, the emergency shutoff can be on the right-hand or the left-hand side, near the far end. It is usually a cable-actuated device, although hydraulic or pneumatic devices may be found.
* Fusible links and nuts. Fusible links or nuts may be found on cable-actuated remote shutoff devices. Should there be a spill fire under or around the tank container, the fusible device will melt, releasing cable tension. Fusible links are required to actuate at temperatures not greater than 2507F (1217C).
Pressure Tank Containers
Pressure tank containers, commonly known as “DOT Spec. 51 Portable” (International – IMO Type 5) containers, are less common in transport. They are pressure tank containers designed to handle internal pressures ranging from 100 to 500 psig. They must be designed for product lading in excess of 1,000 pounds water capacity and have a minimum shell and head thickness of .1875 inches.
DOT specifications for the design and construction of Spec. 51 containers can be referenced in 49 CFR 178.245 and 178.245.7. The DOT requires that Spec. 51 containers be designed and built to the ASME Code and bear an ASME “11” stamp.
Spec. 51 containers are used to transport liquefied gases, such as LPG, chlorine, and anhydrous ammonia; pyrophoric liquids such as aluminum alkyls; and other highly regulated materials, including those products in UN Packing Group 1. Spec. 51 containers will be in the range of 4,500 to 5,500 gallons, although containers as small as 50 gallons can be found (e.g., pyrophoric liquids).
*Dataplates. Each Spec. 51 tank must have a nameplate affixed to either head of the portable tank by soldering, welding, or brazing around the entire perimeter of the plate. The following information is required:
–manufacturer`s serial number,
–U.S. DOT Specification Number (e.g., Spec. 51),
–water capacity (pounds),
–tare weight (pounds),
–design pressure (psig),
–design specific gravity,
–original test date, and
–tank retested at ____ psig on _____ .
*Tank container fittings. The following fittings can be found on Spec. 51 tank containers to make them safe and functional. These fittings may be on the top, at the end, or on the bottom. Generally, the fittings are enclosed with a cover or recessed to protect them from mechanical damage.
* Loading/unloading valves. Liquid and vapor valves are used for filling and emptying the tank. The liquid valve extends into the lading by means of an eduction pipe that may also be fitted with an excess flow check valve. Vapor valves, which also may have an excess flow check valve, are used to remove vapors from the tank or to pressurize the tank for unloading.
All tank outlets must be marked to designate vapor or liquid discharge potential when the tank is filled to the maximum level permitted. They may be threaded or flanged valves. Remember that valve threads may be BSP or metric threads.
* Gauging devices. Gauging devices to measure how much liquid is in the tank may be installed. Various types are found, including the rotary gauge and open and closed gauging devices such as those found on some pressurized railroad tank cars.
* Sample lines. They are used for sampling the lading without opening the tank. Sample lines can develop leaks at the handle or around the plugs.
* Thermometer wells. The thermometer well is used for measuring the lading temperature. Temperature readings can assist responders in determining if a product is expanding and increasing the internal tank pressure. If a thermometer well tube breaks inside the tank container, leaks can develop.
Tank container safety devices. The following safety devices can be found on the Spec. 51 tank containers:
* Safety relief devices. These devices are mounted on top of the container to protect the tank from overpressure under abnormal conditions, such as fire impingement or an internal chemical reaction. These devices may be found inside an unhinged compartment that protects them from the elements.
* Excess flow valves. Excess flow valves may be found on liquid and vapor piping. Mounted inside the tank under the liquid and vapor valves, excess flow valves will stop the product flow if a valve is sheared off. Excess flow valves are operated by gravity or pressure differential.
Specialized Tank Containers
Several specialized tank containers may be encountered, including cryogenic tank containers and tube modules.
* Cryogenic tank containers. They are built to the IMO Type 7 tank container specifications. Cryogenic containers transport cryogenic liquids and refrigerated gases, including argon, oxygen, and helium.
* Tube modules. Tube modules transport pressurized gases in high-pressure 3T cylinders tested to 3,000 or 5,000 psi and permanently mounted within an ISO frame. Examples include oxygen, nitrogen, helium, and hydrogen.
DAMAGE ASSESSMENT FACTORS
Basic factors must be evaluated in all incidents involving tank containers, regardless of their location or the mode of transportation involved. If the container is involved in a rollover or derailment, the risks associated with the incident can rise dramatically. As part of the size-up process, emergency responders must evaluate the following:
Type of intermodal tank involved. Specific factors include the DOT or IM designation (e.g., IM-101, IM-102, DOT Spec. 51), whether the container is pressurized or nonpressurized, the number of compartments, the type of tank metal (e.g., aluminum, stainless steel), and so on.
Nature of the emergency. Scenarios could include leaking attachments, derailment, rollover, being struck by an object, and so on.
Container stress applied to the container tank. It could be mechanical, chemical, thermal, or a combination. Specific evaluation factors can include stress to the container jacket (i.e., insulation), mechanical damage to the tank frame, and corrosion to the container and/or frame.
Jacketed and insulated containers can pose certain issues. If the jacket is damaged and the damage is limited to the outer jacket, the strength of the container may not be compromised. If liquid product is found escaping from the jacket, the actual source of the leak on the container may be at another location remote from the visible point of release.
When dealing with Spec. 51 containers, assessing container damage is critical due to the high container pressures involved. Remember, the higher the internal pressure, the farther the container and product will travel when breached. Also, liquefied gases commonly transported in Spec. 51 containers have tremendous liquid-to-vapor expansion ratios. Special attention must be given to dents with sharp edges or gouges that cross over welds or remove the upper bead of the weld. In these situations, consult the shipper for guidance and advice before moving the tank container.
Type and nature of tank damage. Examples would be a puncture, leaking manway, and bottom valve failure. If the container hasn`t opened up or breached, responders should review the likely types of container breach and consider where the hazardous material will go once it escapes. This is an integral element of the size-up process. Again, the shipper will usually be the best source of technical information regarding the container and likely breach and release scenarios.
Amount of product released and that remaining in the container. The maximum amount of product contained in an intermodal tank container is approximately 6,300 gallons. Responders must evaluate where the incident is now and where the incident will be once tactical operations are implemented. Experience shows that the most common releases from tank containers involve the valves and fittings. When safely possible to do so, you can often control these releases by tightening the valve flange or bolts.
EMERGENCY RESPONSE CONCERNS–TERMINALS
Emergency response concerns at an intermodal terminal facility are a hybrid of the problems and concerns found within each mode of transportation. Specific issues and concerns include the following:
Major ports and terminal areas are extremely busy, with a significant amount of traffic and container movement. Failure to pay attention to one`s surroundings and daydreaming can easily get one injured or killed. Remember to stay alert!
Emergencies at port and terminal facilities can have significant economic and operational impacts on the facility. If an intermodal container is involved in a haz-mat emergency, terminal personnel may attempt to move the involved container to a preidentified isolated location where the problem can be handled without disrupting other terminal operations.
As part of preincident planning activities, responders should identify these locations and evaluate site safety conditions, including surrounding exposures, ground contours, spill control, and overall site safety.
The security and safety departments will typically be key players in the management of any emergency situation at seaports and rail terminals. When dealing with haz-mat emergencies, get a copy of the terminal`s Hazardous Cargo Manifest. This document is similar to the Dangerous Cargo Manifest carried on the container ship. However, the Hazardous Cargo Manifest is a complete computerized printout of each container in the terminal. The manifest will provide the following information:
–proper shipping name of the hazardous material,
–emergency contact (e.g., CHEMTREC(TM)),
–hazard class and UN number,
–trailer number, and
–quantity and weight of the container.
At marine terminals, the U.S. Coast Guard Captain of the Port (COTP) or his designated representative will coordinate all USCG operations. Personnel from the USCG Marine Safety Office (MSO) will be key players in any haz-mat emergency. Remember, the COTP has the authority to regulate and control the movement of vessels and personnel within its area of responsibility, including denying vessels entry into port, prohibiting departure, placing specific operating requirements on vessels, and establishing restricted areas. The authority of the COTP also extends over the land-side areas of all waterfront facilities, such as terminals, piers, and wharves.
Locating and identifying containers holding hazardous materials at terminals can be difficult. While some shipments may not be placarded under DOT regulations, international shipments can be marked and placarded in accordance with IMDG regulations from the point of origin to the final destination, provided the trip is by an ocean carrier.
For example, a container is loaded in Cleveland, Ohio, with drums of “methyl ethyl badstuff.” The container`s ultimate destination is a chemical plant outside Bremen, Germany. The container will be trucked from Cleveland to the Port of Baltimore and loaded on a container ship. In Bremen, the container will be discharged from the vessel and trucked to its final destination. The container is legally marked and placarded in accordance with the IMDG in Cleveland.
By nature of their operations, terminal facilities are also great candidates for technical rescue operations, including high-angle and confined-space situations.
EMERGENCY RESPONSE CONCERNS–FIXED FACILITIES
Temporary storage. Portable tank containers are commonly used as “temporary bulk storage containers” at fixed facilities. Examples include the use of glycol solutions at airports for aircraft de-icing operations; solvents and adhesives at highway and bridge construction sites; and corrosive liquids, oxidizers, and poisons as intermediates for chemical processing operations.
Building and process construction operations are among the greatest potential emergency response problems. Experience shows that since construction projects are temporary and usually unoccupied by the general public, they may not receive the same level of code inspection and enforcement that a fixed facility would receive (e.g. tank farm or chemical storage area). Consequently, portable tank containers often “show up” on the job site and remain for the duration without meeting model fire code provisions for separation and diking.
Permanent and semipermanent storage. There is growing interest in using portable tank containers for fixed-facility permanent storage. In this scenario, the owner intends to incorporate the tank container as a permanent part of the facility`s storage or process area. The advantage of this arrangement is that the owner can lease the tank container or obtain the container as part of a package deal with the supplier (i.e., you buy the product from us, and we`ll supply the tank and install it). If the tank is damaged or requires cleaning, the facility calls the tank owner for a replacement. Be aware that local fire codes must be consulted when these tanks are used for permanent and semipermanent storage.
In some cases, tank containers may be incorporated into the process operation. If the tank container can be directly tied into the process unit, it eliminates the time, effort, and risks associated with product-transfer operations. This arrangement is especially popular among research and development laboratories, where several chemical storage tanks may be required during the life of a special project. When the project is completed, the process is shut down and the tank container is removed.
Loading and offloading methods. Loading and offloading methods for portable tank containers will vary depending on the type of product and container (i.e., liquid vs. gas) and the nature of the hazardous material. In general, open systems may be used for high-flash-point, low vapor pressure materials, whereas closed systems will be used for hazardous materials with low flash points and high vapor pressures.
If a tank container has been breached and cannot be repaired, transferring product or offloading some or all of the product into another compatible tank container may be required. In some situations, it may be possible to immediately use the product as part of a facility`s process operation. Emergency responders should be familiar with the loading and offloading techniques for various types of intermodal tanks.
* * *
Tank containers are classified according to the specification of the portable tank and its fittings. The tank container class determines which products may be transported. The three most widely used specification tank containers permitted to transport hazardous materials in North America are:
IM-101. Used for maximum allowable working pressures from 25.4 psig (1.75 bar) to 100 psig (6.8 bar). Products include nonregulated products and toxic liquids, oxidizers, and flammable liquids with flash points below 327F (1007C).
IM-102. Used for maximum allowable working pressures ranging from 14.5 psig (1.0 bar) to 24.4 psig (1.75 bar). Products include moderate- to low-hazard products such as alcohol, some corrosives, pesticides, resins, solvents, and flammable liquids with flash points between 327F (07C) and 1407F (607C).
Spec. 51. Pressure tank containers designed to handle internal pressures ranging from 100 to 500 psig.
Material of Regulated Nonregulated
Construction Commodities Commodities
Stainless-steel tanks .1875 inches .125 inches Steel tanks .375 inches .25 inches
(Top) Box-type tank container. (Bottom) Beam-type tank container. (Photos by author.)
Intermodal portable tank markings.
Examples of bottom outlet valves.
Tank car fittings section. Examples of container spillboxes and fitting arrangements.
End view of a DOT Spec. 51 pressure tank container showing the valve compartment.
Profile of damage sustained from the derailment of an IM-102 box frame tank container on a flat car.
Leak Control Considerations
Intermodal tank containers are tough and hold up well in high-impact crashes such as truck rollovers and derailments. The majority of the spill and leak situations encountered involve loading and unloading accidents. Common scenarios include loose fittings and valves, overfills caused by product expansion, and “mystery leaks” through the tank shell.
Overfills can be caused when a tank container is overfilled with product without room for expansion. Once the container is subjected to ambient heating after sitting in the hot sun for awhile, product will begin to overflow through the dome, or relief devices may actuate. In this situation, the container must be cooled to reduce the internal pressure and the effects of the ambient heating. As appropriate, product may have to be transferred from the container to reduce the potential for the problem to happen again, and burst discs may need to be replaced.
Another common scenario with tank containers is a “mystery leak” through the tank shell. For example, someone notices liquid dripping from an opening or crack through the insulating jacket in the lower half of the tank. If the tank has not been involved in an accident, the source of the leak is often water that has formed from condensation on the tank. If the outer jacket has been torn from a previous bump or scrape, the inner tank shell is exposed to warm air and sweats. The insulation between the inner tank and outer jacket becomes saturated with water and eventually drips out through openings in the outer jacket. If it is a warm day, the tank has an opening in the outer jacket, and the container has not been involved in an accident, you probably have water on the ground. Good identification procedures and monitoring will usually take the mystery out of the situation.
If product is leaking from the bottom outlet valve cap or blind flange, make sure that the cap or flange is tight. Do not remove the cap without checking the position of the valves! The valve handle should be in the closed position–horizontal to the valve. If the valve handle is in the open position–in line with the valve, activate the remote emergency shutdown handle to close the internal foot valve.
If the bottom outlet valve is leaking and the valve is in the open position, you can activate the remote emergency shutoff on the right side of the tank by pulling the handle. Some emergency shutoffs require that the wire cable running along the side of the tank be pulled.
If a tank container is damaged and the inner tank has been breached, the insulating jacket will make leak control tactics extremely difficult to implement. In this regard, jacketed tank containers share the same problems as jacketed MC-307/DOT-407 and MC-312/DOT-412 cargo tank trucks.
If the tank container is a single-shell container, standard leak control tactics and techniques can usually slow the leak. Critical factors in successful patching and plugging operations will include the pressure of the leak (i.gif>., higher pressures = less effective leak control operations), size and contour of the breach, and compatibility between the chemical and the patching/plugging device.
In rollover situations, the top-side manway may leak because the wing nuts were not properly tightened. These leaks are sometimes caused when the manway wing nuts are tightened sequentially in a clockwise fashion rather than in an alternating fashion (e.g., the way you tighten lug nuts on your automobile`s wheel so the rim and tire are straight). When this situation is encountered, the leak can sometimes be stopped by alternately tightening down the dome clamps.
Remember that Mr. Murphy usually rides shotgun to most haz-mat emergencies. Don`t expect everything to work just the way it was discussed in training. Remember the basics. Look for the quickest, easiest, and best leak-control option that provides safety for the responder. Go with your best option, but always have Plans B and C in your hip pocket. One of the techniques may eventually work.
GREGORY G. NOLL, C.S.P., is a senior partner with Hildebrand & Noll Associates, an emergency planning and response consulting firm. He is also a member of the Lancaster Township (PA) Fire Department and of the Fire Engineering editorial advisory board. The information in this article is taken from the textbook Hazardous Materials Emergencies Involving Intermodal Containers by Gregory Noll and Michael Hildebrand (Fire Protection Publications, 1995).