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Dunnage is a term with a variety of related meanings. Typically dunnage is inexpensive or waste material used to protect and load securing cargo during transportation. Dunnage also refers to material used to support loads and to prop tools and materials up off the ground such as jacks, pipes, and supports for air conditioning and other equipment above the roof of a building.
When unloading a ship, sometimes there is a problem as to what to do with the dunnage. Sometimes the dunnage cannot be landed because of customs duties on imported timber, or quarantine rules to avoid foreign insect pests getting offshore, and as a result often the unwanted dunnage is later furtively jettisoned over side and adds to the area's driftwood problem. According to U.S. and International Law (MARPOL73/78) it is illegal for ships to dump dunnage within 25 nautical miles (46 km) of the shore. Presently, the International Plant Protection Convention (IPPC), an international regulatory agency, mandates its 134 signatory countries to comply with the ISPM 15, which requires all dunnage to be heat treated or fumigated with pesticides and marked with an accredited seal. There are several instances where foreign insects have entered by land and caused devastation to the ecosystem, even ruining crops and causing famine in Africa.
In construction, dunnage is often scrap wood that is placed on the ground and then construction materials are placed on top of it to protect the material from the elements. A classic example of the usage of dunnage is when rebar is placed on a construction site. Dunnage will be placed on the ground and then rebar will be placed on top of the dunnage to allow for easier access and to help protect the rebar. Term “dunnage” is also widely used in construction when referred to the structural elements, supporting various mechanical equipment installed on the roof such as HVAC roof top units, condensers, emergency generators, cooling and chilling towers etc. The purpose of the dunnage system in this case is to transmit the load from the mechanical equipment installed on the roof to the building structural elements such as bearing walls or columns. These kind of dunnages often have attenuating pads and springs, which reduce vibration and noise from mechanical equipment they support.
Dunnage bags are air-filled pouches that can be used to stabilize, secure and protect cargo during transportation. Dunnage bags are placed in the voids between the cargo items. Dunnage bags can be used in all modes of transportation; road, railway, ocean or air.
Originally rubber bags were used to brace pallets inside trucks. They evolved into kraft paper bags with a plastic bag interior. As metal strapping became less popular, many companies now use polyethylene or vinyl- based bags because of their low cost. It is important to match the size of the bag to the void. If this does not match, the bags will not function properly, with potential for damage to cargo and people.
Starting in the 1950s, several US railroad freight carriers started rostering boxcars equipped with load-securing devices to prevent shifting during transit. These cars were usually labeled "Damage Free" or simply "DF". The interior equipment helped to eliminate the need for customer-supplied dunnage.
Dunnage for securing cargo in holds of ships has evolved from wooden boards forming "cribs" to modern mechanical, spring-loaded post-and-socket systems, exemplified by the "pogo sticks" used on US Navy Combat Logistics Force (CLF) ships which provide underway replenishment of stores, spares, repair parts, ammunition, ordnance, and liquids in cans and drums. Dunnage segregates cargo in the hold and prevents shifting of the cargo in response to ship motions.
During the shipbuilding process, dunnage is commonly used term to describe items which are not considered to be part of the ship, but are nevertheless on board the ship. Most often these items are items used by the ship yard in the construction process, but will not remain after the ship is completed. Examples of such items include welding machines, hoses, temporary ladders, and scaffolding.
Miscellaneous uses of term
Outfitters and mule packers use the term dunnage when they transport freight, such as camping gear and food supplies, but do not carry passengers. In fishing net products "dunnage" may refer to a reinforcement of the edges of the net. It is sometimes mistakenly believed to be a nautical term for sewage. It has historically been widely used (UK) as a term for a sailor's personal belongings, as in, "Stow your dunnage and report to the First Mate".