Understanding Coal

This "Chemical of the Quarter" excerpt is from the U.S. Coast Guard Proceedings of the Marine Safety & Security Council magazine by Mr. Richard Bornhorst, Chemical Engineer, U.S. Coast Guard Hazardous Materials Standards Division.

Coal
Editor's Note: Though coal is not a chemical, it does have unique physical and chemical properties. We are providing this information for the safety of those transporting and handling it.

What is it?
Coal is a rock formed by compression of decomposing plant material. Since it is primarily composed of carbon, it is a useful energy source. According to the World Coal Institute website, in 2007, the total world coal production was more than 5.5 billion tons, and coal meets about 26 percent of the world's energy needs and generates about 41 percent of the world's electricity.

How is it shipped?
Coal is generally shipped in bulk quantities either by rail, cargo vessel, or barge. For cargo vessel or barge transport, coal is loaded directly into the cargo hold without mark, count, or any intermediate form of containment such as packaging.

Coal is also sometimes shipped by self-unloading cargo vessels with a conveyor belt system that moves coal from the cargo holds to an unloading arm. A self-unloading cargo vessel is advantageous when it becomes necessary to deliver coal to ports or waterfront facilities that lack the proper shoreside equipment.

The International Maritime Solid Bulk Cargoes (IMSBC) code specifies how coal is loaded, unloaded, and transported by cargo vessel for international shipments. Recent changes to the International Convention for Safety of Life at Sea made the IMSBC code mandatory for all cargo vessels regardless of age, size, or character.

Why should I care?
Shipping concerns. Under the provisions of the IMSBC code, coal is regulated as a hazardous material when transported in bulk by cargo vessel. The code contains provisions for shipping papers, trimming the cargo, segregation, temperature monitoring, and gas detection. All of these provisions will generally apply to coal because of its unique physical and chemical properties.

Health concerns. Exposure to coal dust generated from processing, transporting, or handling coal can cause pneumociosis (black lung), bronchitis, and emphysema. The permissible exposure limit for coal dust is a time-weighted average of 2.4 milligrams per cubic meter over the course of a working period, according to the Occupational Safety and Health Administration. Coal may also deplete the available oxygen in cargo holds and compartments. Some self-heating coals may give off carbon monoxide, which can be toxic at an air concentration as low as 50 parts per million.

Environmental concerns. Although coal is generally not considered toxic or hazardous to the environment, it should be handled carefully and efficiently to minimize releases. Coal can be released into the environment during loading and unloading operations or during routine cleaning (cargo sweeping) operations. Releases from these operations may be prohibited, restricted, or allowed depending upon whether or not they occur in environmentally sensitive areas, coastal or inland waters, or the open sea.

Fire or explosion concerns. Some coals may self-heat spontaneously and emit flammable gases, such as methane. A concentration between five percent and 15 percent methane in air can be flammable or explosive when exposed to a source of ignition. When methane is released from coal stowed on a cargo vessel, it can build up in the cargo hold, thus creating the potential for fire or an explosion. Some self-heating coals may also spontaneously combust during transportation. However, spontaneous combustion is not common. If it does occur, it usually only affects some of the stowed cargo.

What's the Coast Guard doing about it?
Industry has been transporting coal in bulk for many years with relatively few incidents. The safety provisions contained in the IMSBC code have been largely adopted by the coal industry on a voluntary basis. Nonetheless, industry practices will need to be brought into line with the international standards to further improve safety and facilitate the shipping of coal in international commerce.


For more information:
Full article is available at http://www.uscg.mil/proceedings/summer2010.

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