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Friday, 14 January 2011 16:43

Gravel

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Gravel is a loose conglomerate of stones that have been mined from a surface deposit, dredged from a river bottom or obtained from a quarry and crushed into desired sizes. Gravel has a variety of uses, including: for rail beds; in roadways, walkways and roofs; as filler in concrete (often for foundations); in landscaping and gardening; and as a filter medium.

The principal safety and health hazards to those who work with gravel are airborne silica dust, musculoskeletal problems and noise. Free crystalline silicon dioxide occurs naturally in many rocks that are used to make gravel. The silica content of bulk species of stone varies and is not a reliable indicator of the percentage of airborne silica dust in a dust sample. Granite contains about 30% silica by weight. Limestone and marble have less free silica.

Silica can become airborne during quarrying, sawing, crushing, sizing and, to a lesser extent, spreading of gravel. Generation of airborne silica can usually be prevented with water sprays and jets, and sometimes with local exhaust ventilation (LEV). In addition to construction workers, workers exposed to silica dust from gravel include quarry workers, railroad workers and landscape workers. Silicosis is more common among quarry or stone-crushing workers than among construction workers who work with gravel as a finished product. An elevated risk of mortality from pneumoconiosis and other non-malignant respiratory disease has been observed in one cohort of workers in the crushed-stone industry in the United States.

Musculoskeletal problems can occur as a result of manual loading or unloading of gravel or during manual spreading. The larger the individual pieces of stone and the larger the shovel or other tool used, the more difficult it is to manage the material with hand tools. The risk of sprains and strains can be reduced if two or more workers work together on strenuous tasks, and more so if draught animals or powered machines are used. Smaller shovels or rakes carry or push less weight than larger ones and can reduce the risk of musculoskeletal problems.

Noise accompanies mechanical processing or handling of stone or gravel. Stone crushing using a ball mill generates considerable low-frequency noise and vibration. Transporting gravel through metal chutes and mixing it in drums are both noisy processes. Noise can be controlled by using sound-absorbing or -reflecting materials around the ball mill, by using chutes lined with wood or other sound-absorbing (and durable) material or by using noise-insulated mixing drums.

 

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