Your fire department responds to a marine terminal for a report of a gas leak involving an intermodal tank in a container yard. Upon arrival at the marine terminal, the Port Authority Police escorts you to the scene of the incident where you establish an Incident Command Post.
The senior police officer at the scene tells you that the container was offloaded from a container ship about one hour ago. Dock workers smelled a strong odor of gas in the area of the tank and called the Port Police. The area has been isolated and a security perimeter has been established by the Port Authority Police. You cannot smell any gas from your location, which is about 50 yards from the intermodal container.
The Yard Master informs you that a container ship unloaded the propane container about 13:00 hrs and that neither the ships crew or the dock workers smelled gas. He advises you that the marine terminal must resume work as soon as possible so that the ship can meet its sailing schedule. A delay in the scheduled departure will cost thousands of dollars.
The Port Authority Safety Manager joins you at the Incident Command Post and explains that based on his experience with similar containers, it is likely that the Fixed Maximum Liquid Level Gauge may need to be secured so that it is not leaking liquid propane. A survey of the scene has shown that the container is at the top of a stack of containers and will be difficult to reach.
A Combustible Gas Indicator (CGI) reading taken near the bottom of the stack on an instrument calibrated for propane indicates 2% of the Lower Flammable Limit (LFL). A small white vapor cloud can be seen coming from the container valve area. The wind is calm and the temperature is 85º F.
Intermodal pressure tank containers are commonly known as DOT Spec. 51 Portable Tanks or International Maritime Organization (IMO) Type 5 (DOT Spec. 51/IMO Type 5) containers.
Intermodal Containers are designed to be moved on one or more modes of transportation, e.g., from ship to trucks to rail cars. Consequently, they can be found almost anywhere within the transportation system. They may also be found at fixed facilities.
DOT Spec. 51/IMO Type 5 containers are pressurized 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 thickness of .1875 inches. DOT Spec. 51/IMO Type 5 containers used to transport propane will be in the range of 4,500 to 5,500 gallons. However, it is not uncommon to find DOT Spec. 51 tanks having other capacities, depending on customer and shipper requirements.
The portable container is a 40 foot beam constructed unit with 10,610 gallons (40,160 liters) capacity.
The following fittings can be found on DOT Spec. 51/IMO Type 5 tank containers to make them safe and functional. These fittings may be on the top, the end or the bottom. Generally, the fittings are enclosed with a cover or recessed to protect them from mechanical damage. The fittings on the tank shown in this scenario are on the end of the tank. The Pressure Relief Valve is on the top of the tank.
Liquid and vapor valves are used for filling and emptying the tank. The liquid valve extends into the lading by means of an eductor 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 either threaded or flanged valves. However, unlike cargo tank trucks and railroad tank cars, valve threads may be British Standard Pipe (BSP) or metric threads.
Gauging devices may be installed to measure how much liquid is in the tank. Various types are found, including the rotary gauge, and open and closed gauging devices as found on some propane railroad tank cars.
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.
Pressure relief devices are mounted on top of the container to protect the tank from over-pressure under abnormal conditions, such as over-pressure. These devices may be found inside of an unhinged compartment that protects them from the elements.
Excess flow valves may be found on both liquid and vapor piping. Mounted inside of the tank under the liquid and vapor valves, excess flow valves will stop the product flow if a valve is sheared off. Gravity or pressure differential operates excess flow valves.
This device is used to determine when the propane liquid level has reached the maximum level for safe transportation. Propane tanks are normally filled to 80% capacity. During filling operations, the gauge is opened by a technician who observes the gauge while the container is being filled.
When the tank reaches 80% capacity, a small amount of liquid escapes and signals the technician to stop the filling operation. The gauge is then closed and secured.
Fixed Maximum Liquid Level Gauges can develop leaks at the handle or around the plugs. They may initially leak small amounts of liquid that will expand to vapor at a ratio of 1 to 270.
Hoselines or monitors using fog patterns should be placed so that the air entrained in the fog pattern can help dissipate the propane.
NOTE: While propane is 1.5 times heavier than air, it will rapidly dissipate in air. The objective is to keep the propane atmosphere in the vicinity of the leak below the flammable range.
If the Fixed Maximum Liquid Level Gauge is leaking, an attempt should be made to close the valve by screwing the hexagonal nut closed (right-to-tight).
CAUTION: Liquid propane can cause severe frostbite injuries. Neoprene gloves suitable for liquid propane may be needed to avoid injury. Seek assistance from your local propane dealer.
This is an interactive combustible gas meter. Move your mouse or finger (touch device) over the leak area to view the Gas-in-Air percentage change.
This is a top-perspective view of the incident area. Its purpose is only to get the general idea of the incident and surroundings.
In this section, we present an animated version of the incident.